Search Results (352)

Heavy metal pollution due to mining activities poses a significant threat to agricultural production, ecosystem health, and food security in South Africa. This review integrates current knowledge on the use of mustard spinach (Brassica juncea (L.) Czern.) for the bioremediation of polluted water and soil, focusing on enhancing phytoremediation efficiency through the use of silicon-based biostimulant treatments. Mustard spinach is known for its capacity to accumulate and tolerate high levels of toxic metals, such as Pb, Cd, and Hg, owing to its strong physiological and biochemical defense mechanisms, including metal chelation, antioxidant activity, and osmotic adjustment. However, phytoremediation potential is often constrained by the negative impact of heavy metal stress on plant growth. Recent studies have shown that silicon-based biostimulants can alleviate metal toxicity by reducing metal bioavailability, increasing metal immobilization, and improving the antioxidative capacity and growth of plants. Combining silicon amendments with mustard spinach cultivation is a promising, eco-friendly approach to the remediation of mining-impacted soils and waters, potentially restoring agricultural productivity and reducing health risks to the resident populations. This review elucidates the multifaceted mechanisms by which silicon-enhanced phytoremediation operates, including soil chemistry modification, metal sequestration, antioxidant defense, and physiological resilience, while highlighting the practical, field-applicable benefits of this combined approach. Furthermore, it identifies urgent research priorities, such as field validation and the optimization of silicon application methods. Full article

Salinity stress is a primary abiotic constraint limiting global crop productivity, with progressive soil salinization inducing growth inhibition and physiological dysfunction in plants. Although melatonin (MT) has been extensively documented to enhance stress adaptation, the underlying mechanisms through which it mediates salt tolerance by integrating physiological processes remain unclear. This study investigated the effects of varying MT concentrations on photosynthetic performance, plant water relations, water-use efficiency, and stress-responsive physiological parameters in tomatoes, aiming to identify the key physiological pathways for MT-mediated salt stress mitigation. The results showed that salt stress significantly reduced the leaf relative water content and root hydraulic conductivity, suppressed the photosynthetic rate, and ultimately caused significant reductions in the aboveground and root biomass. MT spraying effectively improved leaf water status and root water uptake capacity, enhancing the photosynthetic rate and water-use efficiency, thereby providing material and energy support for plant growth. Furthermore, MT spraying increased the total antioxidant capacity in leaves and promoted the synthesis of phenolic and flavonoid compounds, thereby reducing oxidative damage. Simultaneously, it stimulated the accumulation of osmolytes to enhance cellular osmotic adjustment capacity and optimized ion uptake to maintain cellular ion homeostasis. Among the tested concentrations, 100 μM MT showed the most significant alleviative effects. This concentration comprehensively enhanced the salt tolerance and growth performance of tomato plants by synergistically optimizing water use, photosynthetic function, antioxidant defense, and ion balance. In conclusion, these findings provide experimental evidence for elucidating the physiological mechanisms underlying MT-mediated salt tolerance in tomatoes and offer theoretical references for the rational application of MT in crop production under saline conditions. Full article

Quercus acutissima seeds exhibit high desiccation sensitivity, posing significant challenges for long-term preservation. This study investigates the physiological and metabolic responses of soluble osmoprotectants—particularly soluble proteins and proline—during the desiccation process. Seeds were sampled at three critical moisture content levels: 38.8%, 26.8%, and 14.8%, corresponding to approximately 99%, 52%, and 0% germination, respectively. We measured germination ability, soluble protein content, and proline accumulation, and we performed untargeted metabolomic profiling using LC-MS. Soluble protein levels increased early but declined later during desiccation, while proline levels continuously increased for sustained osmotic adjustment. Metabolomics analysis identified a total of 2802 metabolites, with phenylpropanoids and polyketides (31.12%) and lipids and lipid-like molecules (29.05%) being the most abundant. Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that differentially expressed metabolites were mainly enriched in key pathways such as amino acid metabolism, energy metabolism, and nitrogen metabolism. Notably, most amino acids decreased in content, except for proline, which showed an increasing trend. Tricarboxylic acid cycle intermediates, especially citric acid and isocitric acid, showed significantly decreased levels, indicating energy metabolism imbalance due to uncoordinated consumption without effective replenishment. The reductions in key amino acids such as glutamic acid and aspartic acid further reflected metabolic network disruption. In summary, Q. acutissima seeds fail to establish an effective desiccation tolerance mechanism. The loss of soluble protein-based protection, limited capacity for proline-mediated osmotic regulation, and widespread metabolic disruption collectively lead to irreversible cellular damage. These findings highlight the inherent metabolic vulnerabilities of recalcitrant seeds and suggest potential preservation strategies, such as supplementing critical metabolites (e.g., TCA intermediates) during storage to delay metabolic collapse and mitigate desiccation-induced damage. Full article

In recent decades, heavy metal pollution has become a significant environmental stress factor. Plants are characterized by high biochemical plasticity and can adjust their metabolism to ensure survival under a changing environment. Here we report, to our knowledge, the first gas chromatography-mass spectrometry (GC-MS)-based metabolomics study of Zn-induced stress responses in Amaranthus caudatus plants. The study was performed with root and leaf aqueous methanolic extracts after their lyophilization and sequential derivatization with methoxylamine hydrochloride and N-methyl-N-(trimethylsilyl)trifluoroacetamide. In total, 419 derivatives were detected in the samples, and 144 of them could be putatively annotated. The metabolic shifts in seven-week-old A. caudatus plants in response to a seven-day treatment with 300 µmol/L ZnSO₄·7H₂O in nutrient solution were organ-specific and more pronounced in roots. Most of the responsive metabolites were up-regulated and dominated by sugars and sugar acids. The revealed effects could be attributed to the involvement of these metabolites in osmotic regulation, antioxidant protection and Zn²⁺ complexation. A 59-fold up-regulation of gluconic acid in roots distinctly indicated enhanced glucose oxidation due to oxidative stress upon the Zn treatment. Gluconic acid might be further employed in Zn²⁺ complexation. Pronounced Zn-induced up-regulation of salicylic acid in roots and shoots suggested a key role of this hormone in stress signaling and activation of Zn stress tolerance mechanisms. Overall, our study provides the first insight into the general trends of Zn-induced biochemical rearrangements and main adaptive metabolic shifts in A. caudatus. Full article

Hydrogen peroxide (H₂O₂) functions as a signaling molecule that triggers physiological and biochemical adjustments that help plants cope with environmental stress. This study evaluated the effects of foliar application of 1.5 mM H₂O₂ on the physiological and biochemical responses of Passiflora incarnata subjected to 14 days of drought stress followed by 5 days of rehydration. Drought reduced Fv/Fm and photochemical efficiency, as well as stomatal conductance and transpiration rates. H₂O₂ treatment under drought further reduced stomatal conductance and transpiration, suggesting enhanced water conservation. Drought-stressed plants treated with H₂O₂ exhibited increased concentrations of glucose, fructose, and mannose along with reduced sucrose levels, indicating osmotic adjustment and energy mobilization. Enzymatic antioxidant activity, particularly that of superoxide dismutase and catalase, increased with H₂O₂ treatment, while peroxidase activity remained low. The content of vitexin, arabinose, and trehalose decreased under drought, likely due to their roles in membrane protection, as MDA levels remained stable. After rehydration, Fv/Fm and ΦPSII recovered, and H₂O₂-treated plants showed higher carbon assimilation and carboxylation efficiency. These results indicate that H₂O₂ promotes drought acclimation and enhances post-stress recovery in P. incarnata. We conclude that H₂O₂ induces signaling pathways, with trehalose, arabinose, and vitexin contributing to the regeneration of the photochemical apparatus, as well as defense and acclimation under drought conditions. Full article

In arid agricultural production, exploring suitable water-saving irrigation strategies and analyzing their water-saving mechanisms are of great significance. Alternating partial root-zone drying irrigation (APRI), a water-saving strategy, enhances the water use efficiency (WUE) of alfalfa (Medicago sativa L.) This paper aims to clarify the physiological mechanisms by which the APRI method enhances the physiological WUE of alfalfa, as well as the differences between this water-saving irrigation strategy, conventional irrigation (CI), and their water deficit adjustments, in order to seek higher water use efficiency for alfalfa production in arid regions. In this experiment, alfalfa was used as the research subject, and three irrigation methods, CI, fixed partial root-zone drying (FPRI), and APRI, were set up, each paired with three decreasing moisture supply gradients of 90% water holding capacity (WHC) (W1), 70% WHC (W2), and 50% WHC (W3). Samples were taken and observed once after every three complete irrigation cycles. Through a comparative analysis of the growth status, leaf water status, antioxidant enzyme activity, and osmotic adjustment capabilities of alfalfa under different water supplies for the three irrigation strategies, the following conclusions were drawn: First, the APRI method, through artificially created periodic wet–dry cycles in the rhizosphere soil, provides pseudo-drought stress that enhances the osmotic adjustment capabilities and antioxidant enzyme activity of alfalfa leaves during the early to middle phases of irrigation treatment compared to CI and FPRI methods, resulting in healthier leaf water conditions. Secondly, the stronger drought tolerance and superior growth conditions of alfalfa under the APRI method due to reduced water availability are key factors in enhancing the water use efficiency of alfalfa under this strategy. Full article

Salinity stress is a major environmental challenge that adversely impacts the physiological and biochemical processes of pasture, consequently resulting in reduced yields and compromised quality. Biochar amendment has recently emerged as a promising strategy to alleviate the deleterious effects of salinity stress. However, the interactive influences of salinity stress and wheat straw biochar on the physiological, biochemical, and growth characteristics of alfalfa (Medicago sativa L.) remain underexplored. A factorial experiment was conducted using a randomized complete design with five salinity levels (0, 25, 50, 75, and 100 mM NaCl) and three application rates of biochar (0, 25, and 50 g kg⁻¹) to evaluate wheat straw biochar’s potential in alleviating salinity stress in alfalfa. Results showed that salinity stress increased oxidative stress (hydrogen peroxide and malondialdehyde) and reduced chlorophyll fluorescence (maximum quantum efficiency of photosystem II by 1–27%), leading to decreasing photosynthetic parameters, thereby constraining biomass accumulation by 9–77%. Wheat straw biochar amendment under the highest salinity stress, particularly at 25 g kg⁻¹, mitigated oxidative stress by reducing H₂O₂ and MDA levels by 35% and 33%, respectively, while decreasing the antioxidant enzymes activities of CAT, POD, and SOD by 47%, 42%, and 39%, respectively, compared to the control (non-biochar addition). Concurrently, biochar restored the osmoregulatory substance concentrations of proline and soluble sugar by 59% and 33%, respectively, compared to the control. Furthermore, wheat straw biochar amendment increased the net CO₂ assimilation rate by 98%, thereby increasing biomass by 63%. Our study demonstrates that wheat straw biochar can contribute to protecting alfalfa against salinity stress by modulating physiological and biochemical responses. These findings demonstrate that the 25 g kg⁻¹ wheat straw biochar application had the best performance, suggesting this amendment could be a viable strategy for improving alfalfa productivity in salt-affected soils. Future research should explore long-term field applications and the underlying mechanisms of biochar–plant–soil–plant interactions under diverse saline-alkali environments. Full article

High-temperature stress is one of the main limiting factors for the cultivation and management of cool-season creeping bentgrass (Agrostis stolonifera). The objectives of the current study were to compare physiological changes in heat-tolerant PROVIDENCE and heat-sensitive PENNEAGLE and further identify differential organic metabolites associated with thermotolerance in leaves. Two cultivars were cultivated under optimal conditions (23/19 °C) and high-temperature stress (38/33 °C) for 15 days. Heat stress significantly reduced leaf relative water content, chlorophyll content, and photochemical efficiency, and also resulted in severe oxidative damage to PROVIDENCE and PENNEAGLE. Heat-tolerant PROVIDENCE exhibited 10% less water deficit, 11% lower chlorophyll loss, and significantly lower oxidative damage as well as better cell membrane stability compared with PENNEAGLE under heat stress. Metabolomic analysis further found that PROVIDENCE accumulated more sugars (fructose, tagatose, lyxose, ribose, and 6-deoxy-D-glucose), amino acids (norleucine, allothreonine, and glycine), and other metabolites (lactic acid, ribitol, arabitol, and arbutin) than PENNEAGLE. These metabolites play positive roles in energy supply, osmotic adjustment, antioxidant, and membrane stability. Heat stress significantly decreased the accumulation of tricarboxylic acid cycle-related organic acids in two cultivars, resulting in a metabolic deficit for energy production. However, both PROVIDENCE and PENNEAGLE significantly up-regulated the accumulation of stigmasterol related to the stability of cell membrane systems under heat stress. The current findings provide a better understanding of differential thermotolerance in cool-season turfgrass species. In addition, the data can also be utilized in breeding programs to improve the heat tolerance of other grass species. However, the current study only focused on physiological and metabolic responses to heat stress between two genotypes. It would be better to utilize molecular techniques in future studies to better understand and validate differential heat tolerance in creeping bentgrass species. Full article

While pipecolic acid (Pip) mediates morpho-physiological and molecular responses during biotic stress, its roles under drought remain an inexpressible mystery. The investigation aimed to elucidate the roles of a 30μM Pip pretreatment in alleviating drought injury on barley (Hordeum vulgare L. cv, Bülbül89) seedlings. Pip pretreatment under normal or drought conditions lowered the osmotic potential (Ψs) and water saturation deficit (WSD), while optimizing the relative water content (RWC), triggered osmotically energetic molecules (OEM) and salicylic acid (SA) accumulation, improving osmotic adjustment (OA), and boosting water retention and uptake capacity (WTC, and WUC), alongwith a considerable improvement in seedling growth over non-treated plants under such conditions. Additionally, Pip pretreatment improved chlorophyll (Chl), the chlorophyll stability index (CSI), pheophytin_a, chlorophyllide_a (chlide_a), chlorophyllide_b (chlide_b), chl_a/chlide_a, chl_b/chlide_b, protoporphyrin, Mg-protoporphyrin, protochlorophyllide, and photosynthetic performance over non-treated plants under such conditions. Pip pretreatment preserves redox homeostasis in drought-stressed plants by accumulating antioxidant solutes alongside the activation of superoxide dismutase and glutathione reductase over non-treated plants. Drought distinctly reduced Ψs (more negative), RWC, photosynthetic pigment, CSI, chlorophyll assimilation intermediate, and photosynthetic performance, with an increment in chlorophyll degradation intermediate and nonenzymatic antioxidant solutes. Drought maintains OA capacity via a hyper-accumulation of OEM and SA, which results in higher WSD, WTC, and WUC. Drought triggered an oxidative burst, which was associated with a decline in the membrane stability index. These findings highlight Pip’s capability for lessening drought stress-induced restriction in barley seedlings via bolstering oxidative homeostasis, OA capacity, and stabilizing chlorophyll biosynthesis. Future research must elucidate the precise molecular mechanisms underlying Pip’s action in alleviating drought injury. Full article

Drought including both meteorological drought and water deficiency stress conditions is a major constraint on global agricultural productivity, particularly affecting Brassica species, which are vital oilseed and vegetable crops. As climate change intensifies, understanding plant responses to drought is crucial for improving drought resilience. Drought stress impacts Brassica crops at multiple levels, reducing germination rates, impairing physiological functions such as photosynthesis and water-use efficiency, and triggering oxidative stress due to the accumulation of reactive oxygen species. To counteract these effects, Brassica plants employ various adaptive mechanisms, including osmotic adjustment, antioxidant defense activation, and hormonal regulation. Recent research has explored molecular and physiological pathways involved in drought tolerance, revealing key physiological changes and biochemical markers that could be targeted for crop improvement. This review summarizes the latest findings on the physiological, biochemical, and molecular responses of Brassica crops to drought stress, with an emphasis on adaptive mechanisms and potential drought mitigation strategies. Additionally, future research directions are proposed, focusing on integrating molecular and agronomic approaches to enhance drought resilience in Brassica species. Full article

Thymus capitatus, a Mediterranean medicinal plant, exhibits complex physiological and biochemical responses to environmental stress. This study investigated the effects of drought (40% SWC), salinity (70% SWC + 90 mM NaCl), and their combination (40% SWC + 90 mM NaCl) on the morphological, physiological, and biochemical traits of T. capitatus over 39 days. All stress treatments reduced shoot and root biomass, relative water content, chlorophyll, and carotenoids, with combined stress causing the most severe declines. Proline and soluble sugars accumulated, indicating osmotic adjustment. Total polyphenol content remained stable under single stress but increased under combined stress (123.28 mg GAE/g DW), suggesting an enhanced defense response. Hydrogen peroxide levels surged, particularly under combined stress (7.76 µmol H₂O₂/g FW), reflecting oxidative stress. Essential oil yield declined from 3.22 mL/100 g DW under control conditions to −30% and −34% under drought and combined stress, respectively, while carvacrol content increased (+4.71%) under combined stress, indicating a stress-induced metabolic shift. Antioxidant capacity significantly declined under salt and combined stress, likely due to oxidative stress overwhelming the plant’s defense mechanisms. These findings highlight Thymus capitata’s resilience, with combined stress having the most detrimental impact, followed by drought, while salinity had a more moderate effect. Despite these challenges, the plant retained key bioactive compounds, reinforcing its potential for stress prone environments. Full article

Cadmium (Cd) contamination in agricultural soils is increasing due to anthropogenic activities, posing a significant threat to plant growth and productivity. Phosphorus (P) has been suggested as a potential mitigator of Cd toxicity, yet the role of cotton genotypes with contrasting low-P tolerance in contaminated soils remains largely unexplored. A hydroponic experiment was conducted to assess the effects of Cd stress (5 μM) on Jimian169 (strong-low-P tolerant) and DES926 (weak-low-P tolerant) cotton genotypes under low-P (0.01 mM KH₂PO₄) and normal P (1 mM KH₂PO₄) conditions. The results revealed that Cd stress, especially under low-P, significantly reduced plant growth, dry matter, photosynthetic rate, and P use efficiency (PUE), while increasing oxidative damage through increased malonaldehyde levels and reactive oxygen species accumulation. These adverse impacts were very much evident in DES926 compared to Jimian169. In contrast, Jimian169 demonstrated greater resilience to Cd stress by mitigating oxidative damage through enhanced antioxidant enzyme activity, improved photosynthetic performance, and increased accumulation of osmoprotectants. These findings indicate that Jimian169 can better withstand Cd toxicity by enhancing photosynthesis, antioxidant defense mechanisms, and osmotic adjustment. This makes them a promising candidate for cultivation in Cd-contaminated, P-deficient soils. Full article

Poplars and aspens (Populus L. spp.) are undervalued options for use in managed landscapes. The genus comprises a multitude of taxa often negatively associated with disease susceptibility and short lifespans; however, it also hosts a diverse range of abiotic stress tolerances. The objective of this study was to generate a relative scale of the predicted drought tolerance of Populus spp. to inform site and taxon selection in managed settings. Utilizing vapor pressure osmometry, this study examined seasonal osmotic adjustment and predicted leaf water potential at the turgor loss point (Ψ_po) among several Populus taxa. All evaluated taxa demonstrated the ability to osmotically adjust (ΔΨ_π100) throughout the growing season. Bigtooth aspen (P. grandidentata Michx.) exhibited the most osmotic adjustment (−1.1 MPa), whereas black cottonwood (P. trichocarpa Torr. & A. Gray ex Hook.) exhibited the least (−0.44 MPa). Across the taxa, the estimated mean Ψ_po values in spring and summer were −1.8 MPa and −2.8 MPa, respectively. Chinese aspen (P. cathayana Rehder) exhibited the lowest Ψ_po (−3.32 MPa), whereas black cottonwood exhibited the highest (−2.47 MPa). The results indicate that drought tolerance varies widely among these ten Populus species and hybrids; bigtooth aspen and Chinese aspen are the best suited to tolerating drought in managed landscapes. Full article

Understanding halophyte responses to agronomic management in saline environments is crucial for optimizing their cultivation. This study assessed the physiological and biochemical responses of three halophytic species, ice plant (Mesembryanthemum crystallinum L.), romeritos (Suaeda edulis Flores Olv. and Noguez), and sea asparagus (Salicornia europaea L.) cultivated in half-strength seawater aquaponics (approximately 250 mM NaCl) under the following rooting media treatments: (C) untreated rearing water (RW), (pH) pH-adjusted to 5.5 RW, (pH+S) pH-adjusted to 5.5 RW with nutrient supplementation, and (NS) standard nutrient solution + 5 mM NaCl. Salinity was the primary factor influencing plant responses, while agronomic management played a secondary role. Ice plants exhibited stable growth across treatments due to their strong succulence, high water content, and antioxidative system, requiring minimal management, though optimal pH may enhance nutrient availability. Romeritos showed high treatment variability yet maintained biomass production via Na⁺ compartmentalization, with C treatment supporting better osmotic regulation, while pH adjustments and mineral supplementation induced stress under HSW. Sea asparagus sustained growth across all treatments, likely due to effective K⁺ retention and osmoregulation, reducing the need for additional management. These findings highlight species-specific salinity tolerance mechanisms and suggest that minimal agronomic management can effectively support halophyte cultivation in saline aquaponic systems. Full article

Elevated temperatures and extended drought periods are driving significant changes in the structure and function of forest ecosystems. High-elevation alpine ash forests (Eucalyptus delegatensis R.T. Baker) in Australia are an example of forests that are already impacted by climate change. These obligate seeder forests can shift to non-forest ecosystems following extreme drought and altered fire regimes, raising concern about their adaptation to a rapidly changing environment and long-term forest persistence. Plant functional traits play a major role in determining adaptive mechanisms to environmental conditions. While alpine ash forests are vulnerable to climate change, it is unclear if different provenances have adapted to the climatic conditions in which they grow. We therefore studied the variation in expression of functional traits related to drought tolerance in 21 provenances of alpine ash distributed across an environmental gradient. We investigated if functional traits varied between the provenances and were related to climate of origin in order to identify provenances that may be better adapted to drought. We measured the following traits in a common garden experiment under well-watered conditions: stomatal density, specific leaf area, minimum stomatal conductance and osmotic potential at full turgor. There was very little variation in trait expression between the 21 provenances for all functional traits related to drought tolerance. All provenances had medium-range stomatal density (170–300 stomata mm²) and specific leaf area (SLA, 50–70 cm² g⁻¹), a very low minimum stomatal conductance (2–4 mmol m² s⁻¹) and a high osmotic potential at full turgor (−0.6–0.7 MPa). There was no statistically significant correlation of trait expression with the climate of origin. Thus, there is very little evidence for genetically controlled differences in trait expression of drought tolerance traits in this species. It is likely that the high elevation and high rainfall environment of the species’ ecological niche has not been subjected to frequent and extensive drought periods that would elicit an evolutionary pressure selecting for drought-tolerant traits. We could not identify provenances that would have different drought-tolerant functional trait responses than others, potentially conferring an adaptive advantage under climate change. This has implications for using climate-adjusted provenancing to improve resilience in alpine ash forests predicted to experience more frequent and severe droughts in the future. Full article