Seed Priming Beyond Stress Adaptation: Broadening the Agronomic Horizon

Abstract

Seed priming, traditionally viewed as a method for enhancing crop resilience to abiotic stress, has evolved into a multifaceted agronomic strategy. This review synthesizes the current findings demonstrating that priming influences plant development, metabolic regulation, and yield enhancement even under optimal conditions. By covering a wide range of crops, including cereals (e.g., wheat, maize, rice, and barley) as well as vegetables and horticultural species (e.g., tomato, carrot, spinach, and lettuce), we highlight the broad applicability of priming across agricultural systems. The underlying mechanisms include hormonal modulation, altered source–sink dynamics, accelerated phenology, and epigenetic memory. Various priming techniques are discussed, including hydropriming, osmopriming, biopriming, chemopriming, and nanopriming, with attention to their physiological and molecular effects. Special focus is given to the role of seed priming in advancing climate-smart and precision agriculture. By shifting the narrative from stress mitigation to holistic crop performance optimization, seed priming emerges as a key tool for sustainable agriculture in the face of global challenges.

1. Introduction

Seed priming is often used for improvement of the physiological and biochemical status of the seeds, leading to better performance during germination and early seedling establishment. While its advantage in mitigating abiotic stress conditions such as drought, salinity, and temperature extremes is well documented, its effects under optimal environmental conditions are equally interesting. In intensive agricultural systems, even small gains in uniform emergence, seedling vigor, and final yield can be significant. This paper explores the mechanisms and outcomes of seed priming under optimal growing conditions, focusing on seed quality enhancement, seedling vigor, and yield improvement. While cereals are commonly studied in this context, this review also includes a wide range of vegetable and horticultural crops, highlighting the broad relevance of priming across agricultural systems.

2. Seed Priming and Its Mechanism

Seed germination is a complex physiological process that can be divided into three distinct phases: Phase I (imbibition), Phase II (lag phase), and Phase III (radicle protrusion). In Phase I, dry seeds rapidly absorb water, leading to cell rehydration and activation of metabolism. This is followed by Phase II, a metabolically active but non-growth phase where DNA repair, protein synthesis, antioxidant activation, and mobilization of stored reserves take place. In Phase III, the continuation of cell elongation leads to radicle protrusion, marking the visible onset of germination [1,2]. Seed priming, a pre-sowing technique involving controlled hydration of seeds to initiate metabolic processes without radicle protrusion, has long been recognized for enhancing germination and early seedling growth under stress conditions. The process of controlled hydration activates seed metabolism, including enzyme repair, antioxidant activity, and hormonal signaling, but it is stopped before radicle protrusion (Figure 1). Seed priming strategically targets Phase I and the early portion of Phase II, allowing seeds to activate key metabolic and protective pathways without crossing the threshold into Phase III (Figure 1). This creates a “primed state” within the seed metabolism that enables faster and more synchronized germination upon sowing, especially under stressful conditions [3]. Once primed, seeds are redried to their original moisture content and stored until sowing (Figure 1). The mechanisms behind partial hydration are often complex and involve physiological, biochemical, and molecular changes that happen mainly during Phase II of the germination process. The effects often depend on the specific type of priming used, but the main point of the partial hydration is reactivating metabolic pathways, including respiration and protein synthesis, repairing any cellular damage (which can happen during respiration and storage), accumulating transcripts and enzymes involved in germination, and partial progression through the cell cycle.

Priming methods can be broadly categorized based on the hydration medium and additional biological or chemical inputs. Hydropriming involves seed soaking in distilled water for a defined period, typically followed by drying. It is a cost-effective and easy-to-implement method often used in small-scale farming. Osmopriming employs osmotic solutions such as polyethylene glycol (PEG) or salts to control water uptake more precisely. It allows the seed to remain in a metabolically active state without crossing the threshold into full germination, which enhances regulation over metabolic preconditioning.

Biopriming integrates hydration with microbial inoculants, introducing beneficial bacteria or fungi during the priming phase. These microorganisms promote plant growth, enhance nutrient uptake, and sometimes induce systemic resistance. Hormopriming, on the other hand, uses phytohormones such as gibberellins or salicylic acid to trigger specific signaling pathways associated with seed germination and early vigor. Hardening includes multiple hydration-dehydration cycles and is often employed to improve the robustness and adaptability of the seeds under diverse field conditions. All these priming methods differ in their regulation of water potential but share a common goal: to metabolically precondition of the seed. Nanopriming, an advanced priming method, employs nanoparticles such as metal sulfides (FeS, ZnS, AgS, and CuS), known for their stability and enhanced bioactivity compared with conventional oxides and silver nanoparticles. These metal sulfide nanoparticles significantly influence germination and seedling vigor by modulating antioxidant defenses, reactive oxygen species (ROS) management, and pathogen resistance mechanisms, thus offering substantial agronomic benefits.

3. Classical View: Stress Adaptation Through Priming

With the increasing impact of climate change and accelerated anthropogenic activities, seed priming is emerging as a sustainable approach in agricultural production. Traditionally, seed priming has been studied and applied as a means to improve plant tolerance to abiotic stressors such as drought, salinity, temperature extremes, and heavy metal toxicity (Figure 2). Seed priming techniques such as hydropriming, osmopriming, and thermo- or hormone-priming have been shown to enhance germination, seedling vigor, and stress tolerance in crops like wheat [4,5,6], maize [7], cotton [8], rice [9], chickpea [10], and barley [11] under drought and salinity conditions. Adaptation to both heat and cold stress has become vital for plant survival amid the rise in extreme weather events. Hydropriming and osmopriming with CaCl₂ were used to improve heat tolerance in pea seeds [12], while KNO₃ priming improved heat tolerance in carrot seedlings [13]. Seed priming with salicylic acid (SA) improved the chilling stress in rice [14], while biopriming with Trichoderma harzianum significantly improved maize’s growth parameters under cold stress [15].

Priming can enhance plants’ tolerance to stressors through enhanced antioxidant defense, osmotic adjustment, ion homeostasis, and improved membrane stability. When germinating, primed seeds that are exposed to drought or salinity demonstrate enhanced osmotic adjustment, in which osmotic solutions enable controlled water uptake that activate the metabolic processes necessary for successful germination. Various osmotic solutions such as PEG, sorbitol, mannitol, or inorganic salts (NaCl, KNO₃, CaCl₂, and KCl) can be used as priming agents to enhance plants’ response under drought [16,17], cold [18], or salinity [4,19]. Osmopriming additionally enhances plants’ ability to maintain ion homeostasis by influencing the uptake and compartmentalization of essential and toxic ions, resulting in reduced ion toxicity and improved stress tolerance. For instance, primed wheat seedlings under salinity exhibit higher K⁺/Na⁺ ratios and maintain better photosynthetic efficiency than non-primed seedlings [20]. Similarly, osmoprimed tomato and carrot seeds demonstrate improved germination at suboptimal temperatures [21,22].

Plants usually adapt to stress by boosting their antioxidant defense system, and seed priming activates these mechanisms in Phase II of germination. This involves the upregulation of major detoxifying enzymes, including ascorbate peroxidase (APX), catalase (CAT), and superoxide dismutase (SOD), which play a crucial role in neutralizing reactive oxygen species (ROS) generated under abiotic stress conditions [23,24]. For example, safflower (Carthamus tinctorius L.) seeds primed with melatonin exhibit a dose-dependent response in reducing lipid peroxidation and activating the main antioxidant enzymes under drought conditions [25]. The brassinosteroid 2,4-Epibrassinolide also increases the activity of antioxidant enzymes and reduces the malondialdehyde (MDA) content in rice under heat stress [26]. Similar findings regarding enhanced antioxidant response using seed priming have been observed for cold [27], salinity [28], and heavy metals (HMs) [29].

Recent research highlights metal sulfide nanoparticles as promising nanopriming agents for enhancing tolerance to abiotic stresses. FeS nanoparticles have demonstrated a notable capacity for increasing antioxidant enzyme activities, thereby effectively scavenging ROS and reducing oxidative damage under drought and salinity conditions [30]. ZnS nanoparticles similarly improve seed vigor and physiological stability by enhancing antioxidant defenses and membrane integrity, resulting in more robust seedling establishment under abiotic stresses [31].

Another mechanism of priming, enhancing the plants’ ability to tolerate stress, influences the membrane stability, or the cell membrane’s capacity to preserve its integrity and functionality under various environmental stresses. Seed priming has been shown to reduce electrolyte leakage, thereby enhancing membrane integrity and helping plants better withstand adverse conditions. Jamil et al. [32] demonstrated that priming of Brassica napus L. seeds with distilled water and different concentrations of gibberellic acid (GA3) for 10 h decreases electrolyte leakage under all treatments compared with non-primed seeds. Salt solutions like CaCl₂, KCl, and KNO₃, when used for priming of two barley species (Hordeum vulgare L. Manel. and Hordeum maritimum With.) under increased salinity, effectively reduced membrane damage by lowering electrolyte leakage and the MDA content [33].

Seed priming not only influences the plant itself but also reflects the microbiome in the soil, especially in the rhizosphere. Recent studies highlighted the importance of seed priming in enhancing microbial diversity and richness within root nodules. Seed priming treatments, especially those with certain osmotic agents like sorbitol, have been shown to positively influence the colonization and diversity of beneficial bacteria such as Rhizobium species in legume nodules (Lens culinaris L.) [34]. This improved microbial richness can contribute to better nitrogen fixation, plant growth, and overall soil health.

Seed priming has also been explored as a supportive tool in phytoremediation, particularly in the use of marginal soils contaminated with potentially toxic elements (PTEs). Globally, 14–17% of agricultural soils are estimated to be contaminated with PTEs, posing serious threats to food security and sustainable crop production [35]. Phytoremediation relies on plant species capable of accumulating toxic metals in aboveground tissues while maintaining adequate biomass. However, these traits rarely coexist. Seed priming has shown the potential to improve plant tolerance and metal uptake efficiency while preserving growth, particularly under cadmium [36,37,38,39], lead [40], mercury [41], and nickel stress [2,42].

4. Emerging Functions of Seed Priming Beyond Stress Tolerance

How does seed priming initiate physiological changes that persist throughout plant development? Understanding these early-stage modifications is essential for optimizing priming protocols across species and environments. The pre-sowing hydration-dehydration cycle of priming treatments activates the seeds’ pre-germinative metabolism without initiating radicle protrusion. This controlled activation accelerates metabolic readiness, promoting faster and more uniform germination and emergence. Such synchronization is particularly beneficial for crops requiring precise establishment, as it leads to uniform field emergence, which is critical for downstream agronomic management and yield predictability [43,44].

Molecular and physiological improvements in primed seeds and seedlings are associated with increased seed vigor, which is expressed as an enhanced germination rate, reduced lag time, and greater tolerance to suboptimal sowing depths and planting densities under optimal growth [45,46]. Moreover, priming often widens the thermal window for germination, allowing seeds to germinate rapidly across a broader range of temperatures [44]. As a result, priming not only supports better crop establishment under marginal environments but also boosts performance in high-input agricultural systems, where uniformity and timing are crucial for mechanized cultivation and productivity [43,46].

4.1. Improvement of Seed Vigor and Germination Uniformity

The success of agricultural production is fundamentally linked to rapid and uniform seed germination and seedling emergence. However, under both optimal and suboptimal conditions, many seed lots, especially those with poor physiological quality, fail to meet the desired germination standards. These “low-vigor” seeds typically exhibit delayed germination, poor synchronization, and reduced field establishment. Seed priming, a pre-sowing strategy involving controlled hydration and subsequent dehydration, has emerged as a promising technique to invigorate such seeds and enhance their physiological potential (

Table 1. Overview of seed priming methods and effects on seed germination and seed establishment.

Crop	Priming Method	Seed and Vigor Improvement	Synchrony of Germination	Seedling Establishment
Tomato (Solanum lycopersicum) [10]	Osmopriming (PEG −1.0 MPa)	ATP/ADP ratio, faster radicle emergence	Narrower emergence window, uniform stand	Improved shoot/root ratio
Leek (Allium porrum) [47]	Osmopriming (PEG −1.5 MPa)	Respiration rate, energy metabolism	Synchronized emergence across seed lot	Robust seedling biomass
Carrot (Daucus carota) [47]	Osmopriming (PEG −1.0 MPa)	Enhanced enzymatic activity, faster mobilization of reserves	Reduced variation in emergence time	Stronger hypocotyl elongation
Maize (Zea mays) [48]	Hydropriming and hardening	Shoot and root length, fresh and dry weight	Consistent establishment even in high-density plots	Better field emergence
Lettuce (Lactuca sativa) [47]	Osmopriming (PEG −1.2 MPa)	Improved membrane repair, reduced ROS damage	High uniformity in greenhouse trays	Vigorous transplant-ready seedlings
Sunflower (Helianthus annuus) [47]	Osmopriming (PEG −1.5 MPa)	Catalase and glutathione reductase activity	Stable emergence timing	Higher seedling survival and growth
Spinach (Spinacia oleracea) [47]	Osmopriming (PEG −0.6 MPa)	Antioxidant enzymes, faster germination	Uniform emergence in nursery conditions	Robust seedling architecture
Rice (Oryza sativa) [10]	Hydropriming (12 h in water)	Amylase, improved reserve mobilization	Improved germination timing under nursery set-ups	Improved seedling biomass and shoot elongation
Barley (Hordeum vulgare) [47]	Hydropriming (30 °C, 52% moisture)	ABA levels, cell cycle activity	Faster and synchronized emergence	Stronger seedlings with early vigor
Sugar beet (Beta vulgaris) [47]	Osmopriming (PEG −2.0 MPa)	Respiration rate, improved membrane repair	Uniform emergence even under mechanical sowing	Better stand density in rows
Pepper (Capsicum annuum) [10]	Osmopriming (PEG −1.5 MPa)	Germination enzymes, improved uniformity	Synchronized emergence across variable seeds	Stronger hypocotyl and early leaf development
Primrose (Primula spp.) [48]	Osmopriming (PEG −1.5 MPa)	Homogenized emergence across genotypes	Consistent emergence among different colors	Uniform seedling size for transplanting
Wheat (Triticum aestivum) [49]	Osmopriming (PEG −1.0 MPa, 12 h)	Metabolic enzyme activity and seedling dry weight	Reduced time to 50% germination (T50)	Higher early growth vigor and uniform stands
Chickpea (Cicer arietinum) [50]	Hydropriming (12 h soak in water)	Germination energy and root/shoot length	Uniform emergence across replicates	Stronger root development and early shoot expansion
Cucumber (Cucumis sativus) [50]	Osmopriming (PEG −1.2 MPa)	Enhanced SOD and catalase activity	Synchronized germination in nursery trays	Improved seedling fresh and dry mass
Okra (Abelmoschus esculentus) [50]	Hydropriming (6 h at 25 °C)	Improved membrane integrity and reserve utilization	Reduced variability in emergence time	Robust seedlings with uniform morphology
Eggplant (Solanum melongena) [50]	Osmopriming with KNO3 (1%)	Antioxidant potential and seedling establishment rate	Faster and more uniform germination	Improved seedling length and biomass
Rice (Oryza sativa) [30]	Nanopriming (FeS and MnS nanoparticles)	Improved antioxidant defense and metal assimilation	Enhanced germination kinetics	Increased seedling biomass and shoot elongation
Various crops (e.g., rice, wheat, maize) [51]	Nanopriming with metal and metal oxide nanoparticles	Improved enzymatic activity, water uptake, stress tolerance	Accelerated and more uniform germination	Enhanced seedling vigor and abiotic stress resilience
Stevia (Stevia rebaudiana) [52]	Nanopriming with silica nanoparticles	Increased germination percentage, chlorophyll content, enzymatic activity	Reduced variation in germination timing	Improved physiological status and early growth performance
Forage and medicinal plants (e.g., Trigonella, Nigella, Plantago) [53]	Nanopriming with various nanoparticles (ZnO, TiO2, Fe3O4)	Boosted antioxidant capacity, seed enzyme activity, stress resilience	Accelerated and synchronized germination under abiotic stress	Improved biomass accumulation and stress-adaptive traits
Chickpea (Cicer arietinum) [54]	Biopriming with Bacillus subtilis	Increased root length, improved stress tolerance	More synchronized germination under saline conditions	Stronger and healthier seedlings
Tomato (Solanum lycopersicum “Micro-Tom”) [2]	Biopriming with Paraburkholderia phytofirmans PsJN	Improved chlorophyll content, reduced oxidative stress, enhanced shoot and root growth under Ni stress	Better uniformity under nickel stress	Robust seedlings with enhanced tolerance and physiological performance
Soybean (Glycine max) [55]	Biopriming with Parachlorella, B. subtilis, T. harzianum	Enhanced root and shoot growth, reduced salinity-induced stress markers	More uniform germination under salt stress	Increased seedling vigor and salt tolerance

) [43,46].

4.1.1. Improvements in Germination Parameters

Germination is a complex physiological process involving water uptake, enzyme activation, reserve mobilization, and ultimately radicle protrusion. While the final germination percentage is the most reported metric, a comprehensive assessment of seed performance must include parameters that capture the speed, uniformity, and vigor of germination. These parameters are directly linked to crop establishment and yield [43,44].

The germination percentage quantifies the proportion of viable seeds completing germination under defined conditions. It reflects seed viability but does not indicate how rapidly or uniformly the seeds germinate [46]. In commercial agriculture, a GP ≥ 85% is typically expected for high-quality seed lots. The mean germination time (MGT) is a measure of germination speed, calculated as the weighted average of the time taken for seeds to germinate.

The germination index (GI) incorporates both the percentage and rate of germination. A higher GI indicates not only that more seeds germinate but also that they do so quickly. This index is particularly useful for predicting seedling performance under field conditions, where early emergence is critical [43]. Low synchrony in germination leads to uneven seedling sizes, complicating agronomic management and lowering resource use efficiency. High variation in germination timing is a hallmark of low-vigor seed lots. Priming enhances metabolic synchrony, thereby reducing variation and improving stand uniformity [44]. The seedling vigor index (SVI) combines the GP with the seedling length (shoot or root) to provide a composite measure of the seed’s ability to develop into a robust seedling. It is a reliable predictor of field performance and tolerance to early abiotic stresses [46].

Uniform seeds germinate and emerge simultaneously and directly influence crop establishment, growth consistency, and yield stability [56,57]. Hydropriming is commonly used to promote uniform germination, but its effectiveness largely depends on the duration of soaking. Since the optimal priming duration varies between plant species, it is essential to determine the appropriate timing before conducting the trials. In barley, the optimal soaking time is about 20 h or just before the onset of embryonic axis differentiation [58]. Optimal hydropriming for wheat seeds involves a 12-h incubation period using a water volume equal to the seed’s dry weight. Comparable outcomes can be achieved with an 8-h soak when the water volume is doubled.

Currently, there is ongoing discussion about whether priming improves seed vigor or accelerates germination and provides seed uniformity. Priming tends to be most beneficial for many ornamental plants with heterogeneous seeds and fresh, high-quality seeds, which typically show a stronger response to priming than old or low-quality seeds [59,60]. Seed vigor in rice can be effectively enhanced using 1 mM proline, as demonstrated by an increased germination percentage (GP), germination rate index (GRI), and seedling vigor index (SVI), highlighting its potential as a beneficial priming strategy [61]. Seed priming with 8% soil moisture notably reduced the emergence time and improved seedling vigor throughout, with better shoot and root growth [62]. Seed vigor is largely influenced by genetic background, which determines the inherent potential for germination and seedling growth [62]. However, priming may enhance seed vigor by inducing epigenetic modifications (such as DNA methylation and histone changes) and reshaping transcriptional responses, potentially improving stress tolerance and early seedling performance, though further research is needed to confirm these mechanisms and their long-term effects.

Nanopriming with metal sulfides, including ZnS and AgS nanoparticles, further contributes to yield improvements even under optimal growing conditions. Enhanced chlorophyll biosynthesis, photosynthetic efficiency, and the optimized source–sink dynamics promoted by these nanoparticles lead to significant increases in grain yield, biomass, and harvest index in crops such as maize and wheat [51].

4.1.2. Challenges of Low-Vigor and Poor-Quality Seeds

Low-vigor seeds, often resulting from physiological aging, present a significant challenge to crop productivity and germplasm conservation [56,63,64]. Damage at the molecular level, including membrane deterioration, oxidative stress, and DNA and protein degradation, impairs metabolic reactivation during imbibition, leading to delayed or failed germination [44,65]. Such seeds typically show increased mean germination times (MGTs) [66]. Seed priming can significantly reduce the MGT under both optimal and stressful conditions [45], offering a valuable strategy, particularly in regions lacking cold chain infrastructure for seed preservation. While seed priming offers numerous agronomic benefits, it also presents certain physiological trade-offs that require careful consideration. Primed seeds may undergo accelerated metabolic activation, which can result in faster depletion of internal reserves, particularly if sowing is delayed or environmental conditions are suboptimal. Additionally, the heightened metabolic state may increase sensitivity to abiotic stress during storage or sowing under unfavorable conditions, potentially leading to poor stand establishment. In some cases, primed seeds may germinate more readily under conditions that would naturally inhibit non-primed seeds, potentially inducing maladaptive germination timing in marginal or unpredictable environments.

An additional problem with seeds is suboptimal storage, characterized by high humidity and temperature, accelerating aging. For example, orthodox seeds stored above 60% relative humidity (RH) or 25 °C exhibit a rapid decline in viability [65]. Inadequate drying after harvesting also increases susceptibility to fungal infection and biochemical damage. Also, during harvesting, threshing, or transport, seeds can suffer mechanical injuries. These are often microscopic and go unnoticed during visual inspection but can significantly impair germination by allowing microbial ingress or disrupting embryo integrity [66,67]. For crops like soybean or maize, improper combine harvester settings can cause cracks in the seed coat, increasing the rate of imbibitional injury during rehydration.

Dormancy mechanisms vary by species and can be exacerbated in low-vigor seeds. For instance, seeds with high abscisic acid (ABA) levels or undeveloped embryos may fail to respond to water alone. This is common in wild relatives of legumes and freshly harvested cereals [68]. Priming, especially with gibberellic acid or salicylic acid, has been successful in breaking such dormancy and restoring germination [43].

Prolonged incubations during priming can negatively affect seed quality and performance [69], as a prolonged time can mean that seeds enter the third germination phase. Another concern is observed accelerated deterioration in certain primed seeds during extended storage. Primed seeds are more susceptible to storage-related deterioration, especially under high moisture, moderate temperatures, and prolonged durations [70]. Moreover, some primed seeds show decreased performance and loss of viability after long-term storage, performing worse than non-primed seeds and losing the benefits of priming [71]. Therefore, it is crucial to optimize the timing of seed priming and minimize the storage duration prior to sowing.

4.2. Yield Enhancement Under Optimal Conditions

Priming activates metabolic processes, DNA repair, and antioxidant mobilization, preparing the seed for rapid radicle protrusion upon sowing [43,44]. This metabolic “head start” translates into improved seedling vigor, which under optimal conditions leads to the following:

• Early canopy closure;
• Improved light interception;
• More efficient nutrient and water uptake;
• Reduced intra-specific competition;
• Enhanced sink strength during reproductive phases.

Even slight advancements in germination timing can create competitive advantages during early seedling establishment, which compound throughout the crop cycle, leading to better tillering, biomass accumulation, and reproductive success. Studies across diverse crops, including maize, rice, wheat, and legumes, indicate that seed priming enhances multiple yield-related traits even under non-stressful conditions. For example, Rehman et al. [72] demonstrated that hormonal priming with SA and osmopriming with moringa leaf extract significantly increased the grain yield, biological yield, and 1000-grain weight in spring maize under optimal sowing. These effects were primarily attributed to the improved seedling establishment, increased chlorophyll content, greater leaf area index, and prolonged leaf area duration, all of which contribute to a higher rate of photosynthesis and assimilate partitioning during reproductive stages.

Seed priming has demonstrated the capacity to enhance multiple yield-determining components across a wide range of crops, even when plants are grown under optimal environmental conditions. Among the most critical of these components are the number of tillers or branches, spikelet or pod development, seed size and weight, and the harvest index, or the proportion of total biomass allocated to economic yield. These improvements reflect the influence of priming-induced physiological enhancements that begin at the seed stage and extend throughout the plant’s life cycle [43,44].

One of the impacts of priming is the increase in the number of tillers in cereals or branches in legumes. Enhanced seedling vigor, faster establishment, and early resource acquisition allow primed plants to develop a more expansive vegetative structure, which in turn supports a greater number of reproductive units. This has been demonstrated in wheat, where priming with calcium chloride (CaCl₂) and GA under well-irrigated conditions resulted in increased tiller numbers and ultimately higher spike densities per unit area [9]. Similarly, in legumes such as chickpea and mung bean, primed seeds have been associated with improved branching patterns, which correlate with an increased number of pods per plant [46,73].

Primed plants show increased chlorophyll biosynthesis and accelerated chloroplast development. These changes enhance the light-harvesting capacity and photosynthetic efficiency during the vegetative growth and reproductive stages [43]. The greater photosynthetic capacity translates into elevated source strength and more sugars, amino acids, and assimilates available to support the expanding sink tissues such as spikes, panicles, or pods. Seed priming also modulates the plant’s internal hormonal balance. Primed seeds often exhibit increased endogenous levels of GA and cytokinins (CKs), while ABA levels are either reduced or finely regulated. This hormonal reprogramming supports faster germination, increased cell division in meristematic tissues, and enhanced reproductive organ development [44,74]. The suppression of ABA delays senescence and maintains cellular activity in leaves and developing grains, effectively extending the grain-filling period.

Delayed leaf senescence is a particularly important trait enhanced by priming. By maintaining the chlorophyll content and prolonging the photosynthetically active duration, primed plants continue to accumulate assimilates well into the reproductive stage. This delay in source decline allows for more prolonged starch accumulation and larger seed development, which are especially relevant for cereals such as wheat and rice [9,72].

At the biochemical level, seed priming improves the antioxidant defense system of plants. The activities of key antioxidant enzymes—SOD, CAT, and APX—are enhanced in primed seedlings and maintained at higher levels throughout the plant’s development [73]. Even in the absence of external oxidative stress, high metabolic activities during flowering and grain filling can produce ROS. The primed antioxidant machinery ensures that oxidative damage is minimized, preserving membrane stability, enzymatic functions, and reproductive development.

Grain or seed size and weight are direct indicators of a plant’s ability to sustain and fill developing grains. Primed seeds often result in plants with greater root biomass and water use efficiency, which are critical for sustaining grain filling even under fluctuating microenvironmental conditions within the canopy. In maize, Rehman et al. [72] noted a significant increase in 1000-grain weight and overall biological yields in primed plants compared with their controls. This enhancement was not a response to stress alleviation but rather a manifestation of improved physiological coordination and developmental timing.

The harvest index (HI), or the ratio of the economic yield (grain, seed, or pod) to the total aboveground biomass, is a critical measure of resource use efficiency. Priming often results in a higher HI by improving not just biomass production but the efficiency with which biomass is converted into yield. In wheat, primed plants displayed higher nitrogen uptake and partitioning to reproductive structures, supported by increased stomatal conductance and robust root systems [9]. These coordinated changes enhance sink strength and improve the translocation of assimilates to grains during critical reproductive stages, thereby improving both the yield and harvest index [74].

Evidence for yield improvements under optimal conditions due to seed priming has been reported across a diverse range of crops and environmental contexts. In maize, Rehman et al. [72] demonstrated that priming with salicylic acid (SA) and moringa leaf extract led to grain yield increases of 17–22% under spring sowing without stress. The primed plants exhibited earlier emergence, faster canopy closure, an improved chlorophyll content, and superior source–sink coordination. Enhanced net assimilation rates supported ear development and increased the kernel weight. For rice, Farooq et al. [9] showed that PEG priming under full irrigation enhanced the panicle number per unit area and panicle length. These morphological improvements were coupled with increased grain filling efficiency and better partitioning of biomass toward reproductive structures. The outcome was a significantly higher grain yield without additional fertilizer or irrigation inputs. In wheat, Basra et al. [73] and Ashraf et al. [74] observed that hydropriming and hormonal priming led to increased tillering, spikelet fertility, and grain weights under optimal irrigation and fertilization regimes. These results were attributed to improved early vigor, delayed senescence, and sustained photosynthetic efficiency during grain development. For legumes such as chickpea and soybean, Pawar and Laware [46] reported that priming with GA and KNO₃ improved the pod number, seed weight per plant, and harvest index even under favorable temperatures and soil moisture levels. These outcomes indicate that priming enhances not only the speed of emergence but also long-term reproductive efficiency and metabolic coordination.

5. Metabolic and Developmental Reprogramming

In modern agriculture, optimizing biomass allocation is key to maximizing yields under both optimal and stressful conditions. Seed priming has been explored as a tool to shift source–sink dynamics toward improved assimilate use efficiency, especially during early vegetative stages (Figure 3).

5.1. Alteration of Source–Sink Dynamics

While seed priming has been shown to enhance root development and influence source–sink dynamics, it is important to recognize that these shifts are not universally advantageous. Additional root growth may only benefit the plant if increased below-ground investment aligns with environmental demands, such as nutrient or water scarcity. In high-input or resource-rich systems, excessive root proliferation could represent a suboptimal use of carbohydrate reserves, potentially diverting energy away from reproductive development. Priming-induced modifications in biomass allocation should be interpreted with caution, considering both the physiological context and agronomic goals.

Primed seeds often give rise to plants with altered patterns of source–sink allocation. The “source” refers primarily to the photosynthetically active tissues, mainly leaves, that generate and supply assimilates, while “sink” tissues represent organs that consume or store those assimilates, such as developing grains, pods, tubers, or fruits. Seed priming not only enhances the establishment of stronger and more active source organs but also promotes the development, size, and efficiency of sinks, improving assimilating, partitioning, and overall crop productivity (Figure 3).

Primed seeds often give rise to plants with enhanced leaf area indexes, earlier canopy closure, and greater chlorophyll contents, all of which support improved light interception and photosynthetic capacity during both vegetative and reproductive phases [43,75]. These traits improve source strength, increasing the availability of photo-assimilates for allocation to growing sinks. Simultaneously, seed priming stimulates rapid and synchronized reproductive organ development, leading to more efficient sink establishment [9].

In maize, priming can enhance enzyme activities such as sucrose synthase and invertases in reproductive tissues, potentially supporting sugar mobilization during grain filling [72,76]. Increased expression of sugar transporter genes has also been observed, suggesting more efficient assimilate translocation in some cases [77]. Improved root development is another frequently reported outcome of priming, with improved nutrient and water uptake capacities contributing to enhanced source activity in shoots [9,75]. However, it is important to note that such changes may not always be beneficia; if root proliferation exceeds actual nutrient demand, then it could divert resources away from reproductive development. The coordination of root and shoot function, along with hormonal influences such as elevated cytokinin levels, may delay senescence and support sustained photosynthesis and assimilate flow during grain filling [78,79]. While several studies suggest that priming influences grain filling and reproductive success, it is important to distinguish correlation from causation. Enhanced grain yield and assimilate allocation may result indirectly from improved early establishment, rather than from long-lasting molecular changes triggered by priming itself. Current evidence linking seed priming to late-stage physiological processes such as grain filling remains limited and should be interpreted cautiously. Further mechanistic studies are required to validate these long-distance and delayed effects.

These changes influence assimilate partitioning between source tissues (e.g., photosynthetically active leaves) and sink tissues (e.g., developing seedlings and reproductive organs). Hormonal signaling pathways, including CK, ABA and GA, mediate these responses to coordinate enhanced germination, vegetative growth, and reproductive success.

Under optimal conditions, these enhancements are not compensatory but additive, improving the efficiency of resource allocation without increasing input. As such, priming acts as a developmental signal that reconfigures internal physiological hierarchies in favor of reproductive success and yield quality, making it a powerful tool in high-input, yield-driven agricultural systems.

5.2. Hormonal Crosstalk and Growth Modulation

Seed priming triggers hormonal reprogramming that supports rapid germination and improved seedling establishment, even under optimal conditions. Rather than acting through isolated pathways, priming adjusts the balance of key hormones (gibberellins (GAs), cytokinins (CKs), auxins (AUs), and abscisic acid (ABA)) to coordinate early growth responses [9,43]. One consistent effect is an early rise in GA levels, promoting dormancy release and enzymatic mobilization of endosperm reserves, which accelerates radicle emergence and enhances field performance in crops like rice and wheat [73,74,77].

Cytokinins increase in primed plants, delaying senescence and boosting source activity and sink strength, especially during reproductive development [75,79]. Priming also promotes localized auxin accumulation in roots, enhancing lateral root growth and nutrient uptake [43,77]. ABA levels and ethylene sensitivity typically decline, removing physiological barriers to germination and early root elongation [9,72]. These shifts collectively contribute to faster emergence, improved photosynthetic efficiency, and reproductive success.

Recent studies also point to interactions between priming-induced hormonal rebalancing and transcriptional changes in hormone biosynthesis and signaling genes. For example, PEG-primed tomato and rice seeds show increased expression of GA20ox and IPT genes (involved in GA and cytokinin biosynthesis, respectively), while genes involved in ABA biosynthesis (e.g., 9-cis-epoxycarotenoid dioxygenase-NCED) are downregulated [77,80]. This transcriptional reprogramming suggests that seed priming not only alters immediate hormone levels but also sets the stage for sustained hormonal regulation throughout plant development.

Priming treatments often result in shifts in hormonal balance, particularly reductions in ABA and increases in GA content, leading to expedited germination and enhanced vegetative growth. Hormopriming with agents like salicylic acid or gibberellins further supports this modulation, indicating that priming influences core regulatory networks beyond stress signaling [81]. Most studies present the effects of hormopriming on enhanced overall fitness and yield. In a study on hormopriming of wheatgrass (Agropyron elongatum Host) with GA, CK, ABA and auxin, the primed seeds showed higher germination rates and an overall better physiological response compared with non-primed seeds under control and drought conditions. Although AU decreased the length of the main root while promoting the seminal roots [82], this may be related to the concentration used (50 ppm) and also the AU dual role in root development, which stimulates adventitious and lateral roots [83].

Iqbal et al. [84] hypothesized about the interaction between cytokinin priming and other hormones, particularly auxins and ABA, under salt stress in salt-tolerant and non-tolerant wheat cultivars. While 6-benzylaminopurine (BAP) did not significantly affect ABA levels or alleviate salt stress, kinetin-induced growth was positively correlated with increased indole-3-acetic acid (IAA) levels and negatively correlated with the ABA concentration. Since ABA is one of the key phytohormones involved in the plant response to abiotic stress, its accumulation typically increases under salt stress conditions [85]. With kinetin priming, increase in IAA, and reduction in ABA, these properties shift the hormonal balance toward growth and resilience under salinity stress. Kinetin hormopriming with 3% moringa leaf extract foliar spray also showed positive effects on maize’s physiological response and yields under low and optimal sowing conditions [86]. Exogenous methyl-jasmonate improved physiological and antioxidant responses in wheat under drought, which resulted in a higher dry biomass, number of grains per spike, grain weight, and biological yield [17,87].

Aside from priming with exogenous hormones, other chemicals can also modulate plant responses to stress. Studies indicate that the response varies depending on the priming agent and type of cultivar. In wheat under salt stress, CaCl₂ increased SA levels in the salt-sensitive cultivar and decreased leaf ABA levels. At the same time, CaCl₂ increased IAA and indole butyric acid (IBA) levels in the salt-tolerant cultivar. Conversely, NaCl reduced the concentration of AU in both cultivars but increased the ABA level and reduced the SA level in the salt-tolerant cultivar [84].

Hormonal responses are closely linked to complex gene regulation involving both upregulation and downregulation. While many recent studies describe the effects of hormopriming under different types of abiotic stress, more comprehensive research is required to focus on gene expression, protein-level transcriptional responses, and mechanisms of action.

5.3. Accelerated Phenological Development

Priming shortens the time to flowering and anthesis in multiple crop species. This developmental acceleration offers advantages for adapting cropping systems to shortened growing seasons or avoiding terminal drought.

Seed priming has been increasingly recognized as a potent modulator of crop phenology, even under optimal growth conditions. By triggering early metabolic activation and hormonal adjustments during the imbibition phase, priming initiates a cascade of developmental events that compress the time to reach critical phenological stages, such as germination, vegetative growth, flowering, and maturity, without compromising yield potential. This acceleration offers both agronomic and economic benefits, including synchronized stand establishment, reduced growing cycles, and optimized harvest scheduling.

Primed seeds generally show earlier and more uniform germination, which allows seedlings to gain a temporal advantage in canopy development and root expansion. This head start is critical for early resource acquisition and establishment of shoot–root balance, which strongly influences subsequent phenological events [9,43]. In cereals like wheat and maize, priming treatments such as hydropriming, PEG priming, or salicylic acid priming have been shown to reduce the number of days to emergence, tillering, booting, and heading stages by 3–7 days compared with non-primed controls [72,74]. Such temporal shifts, even if minor, significantly affect overall crop duration and maturity patterns.

This accelerated development is primarily regulated by hormonal cues. Elevated levels of gibberellins and cytokinins in primed plants stimulate cell division and elongation, leading to faster leaf and internode development. Additionally, downregulation of ABA and ethylene biosynthesis pathways reduces developmental delays often associated with dormancy or environmental signal interpretation [77]. In tomato and soybean, priming-induced hormonal shifts led to early flowering and pod initiation, with a more synchronized reproductive phase that contributed to improved yield uniformity [46,79].

Accelerated phenology also affects the duration and dynamics of the grain-filling period. While faster flowering typically shortens the overall crop cycle, primed plants often maintain a photosynthetically active leaf area during the reproductive stages, a phenomenon partially attributed to higher cytokinin activity, which compensates for the compressed timeline and supports effective assimilate loading into grains [78]. This combination of early flowering and extended grain-filling efficiency improves the harvest index without requiring additional inputs. Accelerated development from priming does not sacrifice yield stability. Rather, it enables better alignment of critical phenophases, such as flowering and grain filling, with favorable environmental windows in high-input systems, enhancing temporal resource use efficiency and reducing vulnerability to late-season risks. In time-sensitive or intensive cropping systems, this can improve land use efficiency by allowing double cropping or early market entry.

In conclusion, seed priming functions not only as a vigor-enhancing intervention but also as a temporal regulator, enabling crops to pass through growth phases with greater synchronicity, efficiency, and coordination. This acceleration of phenological development, coupled with improved physiological resilience, represents a key mechanism through which priming enhances both crop performance and farming system flexibility.

6. Applications in Climate-Smart and Precision Agriculture

While hormonal signaling plays a central role in plant growth and development, its reprogramming by seed priming remains only partially understood. Disentangling how phytohormones coordinate the primed response offers insights into developmental plasticity and resilience mechanisms.

6.1. Use in Marginal Soils and Ecological Restoration

The environment is most often contaminated with a mixture of components such as HMs and polycyclic aromatic hydrocarbons (PAHs), originating from various anthropogenic sources such as mining, industrial waste disposal, agricultural chemicals, vehicle emissions, and metal processing [88]. A large portion of research studies are currently investigating innovative solutions for soil remediation and detoxification. The best results are obtained by combining physical methods with assisted phytoremediation [89]. Modern agricultural land faces increasing contamination from complex mixtures of pollutants such as HMs and PAHs, often originating from mining, industrial effluents, pesticides, and vehicular emissions [88]. Conventional remediation methods are costly and slow, prompting the search for phytoremediation and ecological restoration strategies that leverage plant resilience.

Seed priming has been identified as a valuable intervention to enhance plant tolerance to such stress and improve phytoremediation potential. For example, Abubakar et al. [90] demonstrated that microwave and ascorbic acid priming of spinach (Spinacia oleracea L.) seeds improved growth and enhanced phytoextraction of Pb, Cd, and Ni from surgical effluents. Similarly, Karalija et al. [38] showed that Silene sendtneri, a cadmium hyperaccumulator, exhibited significantly enhanced shoot Cd accumulation following priming with 1 mM SA. Priming enhances plant performance in saline, metal-contaminated, and degraded soils, making it a potential tool in phytoremediation and ecological restoration. Abubakar et al. [90] evaluated the use of spinach (Spinacia oleracea L.) in phytoextraction of HMs from surgical industry effluents. Spinach seeds were primed with microwave irradiation and ascorbic acid, which enhanced germination, plant growth, and HM (Pb, Cd, and Ni) uptake in roots, stems, and leaves, making it a promising method for phytoextraction. A novel hyperaccumulator, Silene sendtneri, was evaluated for the potential remediation of Cd-contaminated soils using seed priming with various combinations of agents such as distilled water, silicic acid (SiA), SA, and proline. While seed priming generally enhanced germination and Cd tolerance, the highest accumulation of Cd in shoots was recorded after 1 mM of SA seed priming [38].

Intercropping systems with primed accumulator species may further augment these benefits. While legumes are mostly used as intercrops, the best hyperaccumulation properties show species from the Crassulaceae family [91]. Enhancing hyperaccumulators for improved heavy metal uptake [38] or protecting crops within intercropping systems are among the approaches that warrant further investigation regarding the application of seed priming in the rehabilitation of contaminated soils. Intercropping systems involving primed hyperaccumulator species have shown synergistic benefits in detoxifying soils. While legumes are common intercrops, members of the Crassulaceae family show excellent heavy metal accumulation potential, suggesting a broader set of candidate species for primed intercropping [91]. Priming these plants with growth regulators or osmoprotectants such as proline or silicon can further enhance metal tolerance and uptake efficiency [38,89].

More than 33% of global land is degraded by different anthropological activities, predominantly rapid urbanization and agriculture development. Soil restoration could be long and expensive, but using these marginal soils by employing different methods to improve plant resilience can be a feasible solution. Micronutrient deficiency is a widespread constraint on crop productivity and human nutrition. Seed priming offers a targeted method to improve early nutrient availability and potentially biofortify plants from the earliest stages of growth. Seed priming with a micronutrient solution is a promising technique for maize in micronutrient-deficient soils, which is one of the major limitations for crop production in South Africa [92]. Micronutrient-based seed priming serves a dual function; it not only enhances early metabolic activation but also enables pre-sowing biofortification of seeds, compensating for micronutrient-deficient soils. This is particularly relevant in regions where zinc or iron availability is low due to the soil pH or organic matter composition. For example, Zn priming has been shown to improve seedling vigor and increase grain zinc concentrations in both maize and wheat, thereby contributing to yield improvement and nutritional quality. Such applications position micronutrient priming as a cost-effective and agronomically viable strategy for sustainable intensification. Zn priming of maize seed hybrids also improved plant growth, biomass, and grain yields in Zn-deficient calcareous chernozem [93]. Marginal soil usage also includes nutrient-depleted areas, which represent a critical barrier to crop productivity. In South Africa, Nciizah et al. [92] demonstrated that maize primed with micronutrients outperformed unprimed controls in zinc-deficient soils. A similar study on chernozem soils showed that zinc priming enhanced the growth and yield of maize hybrids [86], confirming the relevance of seed priming in soil restoration and productivity enhancement across agroecological zones.

6.2. Tailored Priming for Cropping Systems and Technologies

As agriculture shifts toward automation and data-driven management, priming is increasingly integrated into seed enhancement technologies (SETs), particularly for direct-seeded and drone-assisted precision farming. In these contexts, priming not only boosts seed performance but also ensures uniform emergence and reduced vulnerability during early seedling stages [94]. Priming is increasingly integrated into SETs, enabling precise sowing in directly seeded or drone-assisted agriculture. A primary goal of SETs is to enable uniform seed germination, improve seeds’ physiological traits, and help alleviate both biotic and abiotic stress. Priming techniques represent a rapid and affordable option to enhance seed resilience [94].

Tailored protocols for short-season varieties, intercropping, and conservation agriculture are under development. Most of the recommended procedures and protocols include hydropriming, or soaking seeds for a specific period to enhance seed germination in semi-arid and arid areas in marginal and low-resource settings. Hydropriming for 8 h combined with microfertilization can enhance crop and fodder production by 50%, with increased land productivity and reduced labor [95]. These results have a significant socio-economic impact on people living in the Sub-Saharan region with limited resources and knowledge regarding modern agriculture technologies. Global organizations such as the Food and Agriculture Organization of the United Nations (FAO) are introducing priming as an important tool to combine with other known low-cost techniques to achieve maximum germination [96]. On-farm seed priming was demonstrated to be a simple, low-cost, scalable, and transformational strategy for improving crop establishment, yield, and overall farm productivity. In addition, this enabled farmers in resource-limited, rain-dependent systems to increase crop yields while reducing risk with few inputs [97]. Tailored priming protocols are being developed for specific cropping systems, including conservation agriculture, intercropping, and short-season varieties. In arid and semi-arid regions, hydropriming has been widely adopted. When combined with microfertilization, hydropriming for 8 h can increase yields by over 50%, according to Liniger et al. [95]. Such practices are already transforming low-input systems in Sub-Saharan Africa, enhancing food security and land productivity with minimal cost.

Many reported examples of seed priming primarily involve hydropriming, leading to a prevailing perception in the literature that priming is best suited for marginal soils and resource-limited environments. Despite its potential, standardized and broadly accepted protocols beyond hydropriming remain limited, underlining the critical need for the development of consistent, scientifically robust methodologies adapted to the diverse cropping systems and evolving agricultural technologies. On-farm seed priming has been shown to be one of the most accessible and transformative agricultural practices in rain-fed systems. A study by Harris et al. [97] in India showed that simple soaking of seeds before sowing significantly improved crop establishment, yields, and farmer income. Similarly, Sissoko et al. [98] reported that over 85% of households participating in climate-smart farming programs in Mali adopted seed priming. These interventions led to cereal yield increases of 418–673 kg/ha and extended food security by an average of two months per year.

Despite its potential, much of the literature continues to associate priming with basic hydropriming. While this method remains vital, the full spectrum of priming, encompassing hormonal, chemical, nano-, and biopriming, offers broader and more potent solutions. Achieving this would unlock priming’s role in sustainable intensification and contribute to global agricultural resilience in the face of climate uncertainty [99].

7. Integration of Omics for Mechanistic Insights and Marker Discovery

The integration of multi-omics approaches, transcriptomics, proteomics, metabolomics, and epigenomics has revolutionized our understanding of seed priming, providing deep mechanistic insights into the molecular reprogramming it induces. These techniques allow for the dissection of complex biological processes involved in enhanced germination, vigor, and stress resilience and offer a powerful platform for the identification of biomarkers for priming efficiency across diverse species.

7.1. Transcriptomic Reprogramming and Priming Duration

High-throughput transcriptomic analyses have identified multiple priming-responsive pathways, including those related to energy metabolism, cell cycle regulation, cell wall modification, and ROS detoxification. The analysis of hydroprimed sunflower seeds, which generally enhanced germination by shortening the time to radicle emergence, also revealed through transcriptomic profiling that gene expression patterns varied depending on the specific duration of the priming treatment. Expansin genes involved in cell wall loosening were upregulated, indicating their role in radicle protrusion and seed germination [100] and making them a potential marker to assess seed priming efficiency in Helianthus annuus.

Seed priming activates both DNA repair mechanisms and antioxidative response genes, improving genome stability and stress resilience, which together represent promising targets for identifying biomarkers of priming efficiency. In Arabidopsis, overexpression of AtOGG1 increased seed resistance and the germination rate and reduced the levels of 8-hydroxy-2′-deoxyguanosine (8-oxo-dG), a marker of oxidative DNA damage [101]. AtOGG1 is a crucial enzyme in the base excision repair (BER) pathway and is responsible for genome stability. This indicator is especially important for testing seed priming efficiency under abiotic stress conditions, although it needs to be further validated in other species.

Sharma and Maheshwari [102] monitored changes in the expression of genes involved in various DNA repair pathways, such as GTF II H2, MMZ3/UEV 1C, RAD3, Rec A-like 1, RAD54, uracil-DNA glycosylase, and KU80, in chickpea under different priming conditions. These genes are linked to nucleotide excision repair (NER), BER, homologous recombination (HR), and non-homologous end joining (NHEJ), suggesting that seed priming can robustly activate DNA repair responses.

7.2. Proteomic and Antioxidative Response

Osmopriming with 320 mM NaCl in Solanum melongena upregulated genes involved in antioxidative defenses, such as APX, SOD, CAT, and glutathione reductase, while higher concentrations or uncontrolled rehydration increased DNA damage and ROS formation [103]. Biopriming with Bacillus spp. and hydropriming also significantly upregulated DNA repair and antioxidant response genes [104]. These findings support the role of priming in activating multiple protective pathways that are not only essential under stress but may also optimize seed physiology under favorable conditions.

Dehydrin CAP85 (Spinach dehydrin gene) seems to play an important role in seed development, regulating chill and desiccation in Spinacia oleracea when osmoprimed with 0.6 MPa PEG 8000 at 15 °C. The study observed the accumulation of three different dehydrin-like proteins (DLPs) to the amounts of 30, 26, and 19 kDa, which improved seed germination under mentioned stress conditions. DLPs belong to Group II late embryogenesis abundant (LEA) proteins and are generally involved in seed germination and mitigation of abiotic stressors [105].

7.3. Metabolomic and Functional Insights

Metabolomic profiling complements transcriptomic and proteomic data by identifying small molecules that change during priming, particularly osmoprotectants, antioxidants, and energy substrates. In rice, increased levels of proline, sugars (raffinose and trehalose), and polyamines were observed following seed priming, facilitating osmotic adjustment and membrane stabilization. These metabolite profiles serve as biochemical markers of metabolic readiness and seed vigor.

In a comprehensive study of sugar beet proteomics, hydropriming activated the methyl cycle, protein synthesis, and lipid and starch mobilization pathways which are closely linked to vigor enhancement. As potential biomarkers for seed vigor, Catusse et al. [106] highlighted isocitrate lyase, components of translational machinery, and proteins involved in ABA signaling.

7.4. Epigenomic Regulation and Transgenerational Memory

Emerging evidence suggests that priming induces epigenetic modifications, such as DNA methylation and histone acetylation, which contribute to stress memory and may be transmitted transgenerationally. Although primarily studied in model plants, DNA methylation profiling in rice and Arabidopsis indicates that seed priming may establish epigenetic marks that modulate gene expression involved in stress responses and metabolic regulation [44]. These epigenetic markers may offer new avenues for developing priming protocols with long-lasting effects, especially when combined with breeding strategies targeting stress-adaptive traits.

7.5. Toward Biomarker-Guided Precision Priming

By identifying key molecular indicators associated with seed priming, it becomes possible to develop reliable biomarkers that can predict the effectiveness and success of priming treatments. These may include expansin genes (for cell wall loosening), AtOGG1 and KU80 (for DNA repair), DLPs (for dehydration tolerance), and metabolite profiles rich in compatible solutes and antioxidants. This capability would not only facilitate the rapid assessment of seed quality and vigor but also enable the optimization of priming protocols tailored to specific species or environmental conditions.

The integration of omics data into seed technology pipelines could thus support the development of precision agriculture practices, where seeds are evaluated and optimized at the molecular level before field deployment. Future research should prioritize multi-omics meta-analyses across species, stress types, and priming agents to create robust databases and decision support tools for the seed industry and farmers.

8. Seed Industry and Commercial Considerations

Can seed priming be scaled reliably within the commercial seed sector without compromising storability and uniformity? The loss of seed longevity is primarily attributed to increased susceptibility to oxidative stress, where ROS damage vital macromolecules such as DNA, RNA, proteins, and lipids. While seeds possess innate defense systems, including antioxidant enzymes (SOD and CAT), DNA repair pathways, and accumulation of LEA proteins, primed seeds may enter storage with a compromised protective state unless additional stabilization steps are taken.

Drying techniques post priming play a critical role in seed shelf life. Slow and controlled drying is superior to rapid or surface drying as it helps maintain the functional integrity of LEA proteins and heat shock proteins (HSPs), both of which stabilize membranes and cellular structures under desiccation stress. Moreover, heat shock pretreatments have been shown to further extend seed viability by preconditioning the seeds’ molecular chaperone systems. Storage temperature is another essential factor. While some crops (e.g., rice and tomato) benefit from the cold storage at 4 °C, others like sweet corn require moderately higher temperatures. Defining optimal storage protocols for each crop remains a major challenge, necessitating further research on species-specific post-priming physiology. At the molecular level, manipulating the cell cycle checkpoint through compounds like mimosine and hydroxyurea can significantly improve storability. These agents likely delay the reinitiation of DNA replication, preserving the primed metabolic state without accelerating deterioration.

To ensure market scalability, standardization of priming protocols is essential. This includes defining soaking durations, drying temperatures, acceptable seed moisture contents, and seed lot uniformity. The quality control systems must monitor physiological and biochemical markers post priming to ensure consistent performance. The development of coating technologies that combine drying agents, protectants, and metabolic inhibitors could help stabilize the primed state and improve transportability, storability, and shelf life, crucial factors for the successful integration of primed seeds into global seed markets.

9. Future Directions and Research Gaps

Despite all the progress in priming research, several critical knowledge gaps remain that limit their full potential in precision agriculture and global seed systems.

First, understanding the genetic and epigenetic basis of priming responsiveness is paramount. While priming has been linked to activation of DNA repair, antioxidant defense, and hormonal pathways, the underlying regulatory networks and heritable modifications remain poorly defined. Further investigation into transgenerational effects, particularly the inheritance of stress memory and metabolic priming across plant generations, could revolutionize breeding strategies for stress-resilient crops. Second, standardized protocols for field validation across diverse agroecological zones are urgently needed. Many studies reported promising outcomes under controlled conditions, but these do not always translate to field success due to variability in soil, weather, seed batch quality, and local management practices. Third, the integration of multi-omics approaches (transcriptomics, proteomics, metabolomics, and epigenomics) is essential to identify robust biomarkers of priming efficiency. This would enable precise screening of seed lots and help tailor priming formulations to specific genotypes and environmental scenarios.

Additionally, new research should address the following:

• Thresholds of water imbibition during priming to avoid premature germination while activating beneficial metabolic responses;
• The interaction of primed seeds with soil microbiota, including effects on rhizosphere dynamics and the microbial community;
• Combinatorial priming protocols, involving dual stress simulations (e.g., salt + heat or drought + metal) or hybrid methods (e.g., nano-biopriming);
• Socioeconomic barriers to adoption in smallholder contexts, including accessibility, cost, and farmer awareness;
• Environmental impact assessment of novel priming agents (e.g., nanoparticles) to ensure sustainability and regulatory compliance.

Investments in seed priming automation technologies, smart drying systems, and coating innovations can bridge the gap between lab-scale research and commercial production, enhancing the scalability and reliability of primed seeds in climate-smart agricultural systems.

10. Conclusions

Seed priming has emerged as a transformative and scientifically grounded strategy to enhance crop performance, offering a powerful means to boost seed quality, seedling vigor, and eventual yields. Through a cascade of physiological, biochemical, and molecular changes, priming enables seeds to enter a heightened state of readiness that accelerates germination, improves uniformity, and forties plants against environmental challenges. These benefits extend beyond stress mitigation; primed seeds often outperform untreated ones even under optimal growing conditions due to enhanced source–sink coordination, hormonal balance, and phenological advancement.

The mechanistic background of seed priming involves a complex interplay of metabolic reprogramming, cellular detoxification, hormonal crosstalk, and DNA repair activation, all of which synergistically contribute to improved plant resilience. Omics-based research has illuminated these processes further, identifying key genes, proteins, and metabolites associated with priming-induced responses and thereby providing robust molecular markers for seed vigor and stress adaptability. Integration of transcriptomics, proteomics, and metabolomics has not only clarified the dynamic shifts during priming but has also opened new avenues for precision agriculture and marker-assisted seed enhancement.

Advanced priming technologies, such as biopriming, nanopriming, and hybrid chemical-biological formulations, are expanding the toolkit available to seed technologists and agronomists. These methods allow for the development of customized protocols tailored to specific crop genotypes, stress environments, and farming systems. Furthermore, the combination of seed priming with coated seed technologies, drone-assisted sowing, and intercropping with accumulator species holds significant promise for climate-smart agriculture and ecological restoration, particularly for marginal and contaminated soils.

Despite these advances, challenges persist. Priming can compromise seed storability, posing logistical issues for commercial distribution and long-term seed banking. Moreover, the lack of standardized, species-specific protocols and inconsistent field outcomes limit broader adoption. Addressing these gaps will require cross-disciplinary efforts combining plant physiology, molecular biology, agronomy, and seed technology.

Looking ahead, the future of seed priming lies in its integration into sustainable intensification strategies, where it serves not only as a resilience-enhancing tool but also as a platform for innovation in seed science. Standardizing priming protocols, understanding genotype-specific responses, and developing reliable quality control systems will be pivotal in scaling priming for industrial use. Moreover, advancing our knowledge of epigenetic inheritance and microbiome interactions can unlock the next generation of smart seeds capable of adaptive memory and context-specific responses.

In the context of a changing climate, increasing food demands, and land degradation, seed priming represents a low-cost, high-impact solution. Its capacity to enhance germination, bolster yields, and build stress resilience makes it indispensable for both traditional farming systems and modern precision agriculture. With continued research, innovation, and collaborative implementation, seed priming can play a central role in shaping the future of sustainable and productive global agriculture.