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Review

Advances in Boron, Iron, Manganese, and Zinc Signaling, Transport, and Functional Integration for Enhancing Cotton Nutrient Efficiency and Yield—A Review

by
Unius Arinaitwe
1,*,
Dalitso Noble Yabwalo
1,
Abraham Hangamaisho
2,
Shillah Kwikiiriza
3 and
Francis Akitwine
3
1
Department of Agronomy, Horticulture, and Plant Science, South Dakota State University, Brookings, SD 57007, USA
2
Department of Plant Pathology, North Dakota State University, Fargo, ND 58102, USA
3
Department of Agronomy, Iowa State University, Ames, IA 50011, USA
*
Author to whom correspondence should be addressed.
Int. J. Plant Biol. 2026, 17(1), 7; https://doi.org/10.3390/ijpb17010007
Submission received: 10 December 2025 / Revised: 12 January 2026 / Accepted: 15 January 2026 / Published: 20 January 2026
(This article belongs to the Topic Recent Progress in Plant Nutrition Research and Plant Physiology: 2nd Edition)
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Abstract

Micronutrients, particularly boron (B), iron (Fe), manganese (Mn), and zinc (Zn), are pivotal for cotton (Gossypium spp.) growth, reproductive success, and fiber quality. However, their critical roles are often overlooked in fertility programs focused primarily on macronutrients. This review synthesizes recent advances in the physiological, molecular, and agronomic understanding of B, Fe, Mn, and Zn in cotton production. The overarching goal is to elucidate their impact on cotton nutrient use efficiency (NUE). Drawing from the peer-reviewed literature, we highlight how these micronutrients regulate essential processes, including photosynthesis, cell wall integrity, hormone signaling, and stress remediation. These processes directly influence root development, boll retention, and fiber quality. As a result, deficiencies in these micronutrients contribute to significant yield gaps even when macronutrients are sufficiently supplied. Key genes, including Boron Transporter 1 (BOR1), Iron-Regulated Transporter 1 (IRT1), Natural Resistance-Associated Macrophage Protein 1 (NRAMP1), Zinc-Regulated Transporter/Iron-Regulated Transporter-like Protein (ZIP), and Gossypium hirsutum Zinc/Iron-regulated transporter-like Protein 3 (GhZIP3), are crucial for mediating micronutrient uptake and homeostasis. These genes can be leveraged in breeding for high-yielding, nutrient-efficient cotton varieties. In addition to molecular hacks, advanced phenotyping technologies, such as unmanned aerial vehicles (UAVs) and single-cell RNA sequencing (scRNA-seq; a technology that measures gene expression at single-cell level, enabling the high-resolution analysis of cellular diversity and the identification of rare cell types), provide novel avenues for identifying nutrient-efficient genotypes and elucidating regulatory networks. Future research directions should include leveraging microRNAs, CRISPR-based gene editing, and precision nutrient management to enhance the use efficiency of B, Fe, Mn, and Zn. These approaches are essential for addressing environmental challenges and closing persistent yield gaps within sustainable cotton production systems.

1. Introduction

Cotton is a vital global agricultural commodity crop in food, feed, and industrial uses. The United States (U.S.) is among the world’s leading producers, ranking fourth globally with an annual output of 14.6 million bales of lint and a national average yield of 1059 kg ha−1. The US’s cotton yield is well above the world average of 792 kg ha−1 [1]. Cotton is cultivated across a broad geographic extent in the U.S., from Virginia to California, with Texas, Georgia, and Mississippi as the top producing states [1]. While the U.S. is the world’s largest cotton exporter, China remains the leading importer [1,2]. Like other crops, cotton growth and yield depends on the availability of both macro and micronutrients. The latter are only demanded by plants in trace quantities but are indispensable in sustaining the metabolic processes that drive cotton growth, reproduction, and fiber development.
Out of nearly 90 elements occurring naturally in soils, only a limited number are classified as essential micronutrients, and among them, iron (Fe), zinc (Zn), manganese (Mn), and boron (B) play critical roles in sustaining cotton yield [3]. Each plays a unique role that directly influences cotton growth traits. Boron, for example, is essential for cell wall formation, membrane integrity, and reproductive structures formation [4,5]. Iron on the other hand regulates chlorophyll biosynthesis, photosynthetic electron transport, and energy metabolism [6,7,8]. Manganese functions as a cofactor for enzymes in photosystem II, critical for lignin biosynthesis and oxidative stress regulation [9]. Zinc contributes to auxin synthesis, enzyme activation, and reproductive organ development [10]. These roles of micronutrients are linked to several physiological and molecular mechanisms that influence their effects on yield, yet their management has long been overshadowed by the emphasis on nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) [7,11,12,13,14,15,16,17].
Given the global significance of cotton as both an economic and industrial crop, it is imperative to reevaluate the current advances, mechanisms, and contributions of B, Fe, Mn, and Zn in cotton growth and yield formation. This review integrates current physiological, molecular, and agronomic insights on B, Fe, Mn, and Zn in cotton. The overarching objective is to clarify their role in signaling pathways, transport mechanisms, and functional interactions in cotton, thereby defining opportunities for improving micronutrient use efficiency and identifying future research priorities.

2. Methodology

To ensure a comprehensive, transparent, and reproducible synthesis of current knowledge, this review employed a structured and systematic approach to identify scholarly work on the roles of boron, iron, manganese, and zinc in cotton. Additional emphasis was placed on mechanisms involved in micronutrient signaling, transport, and utilization in cotton.
A systematic literature search was conducted across major scientific databases, including Scopus, Web of Science, PubMed, and Google Scholar. The search primarily targeted studies published in English from January 2000 to March 2025 to capture contemporary advances in plant physiology, molecular genetics, and precision nutrient management. Earlier foundational studies (prior to 2000) were included selectively only when they provided essential insights into micronutrient functions or historical context for the development of current knowledge. Search terms combined keywords and Boolean operators such as “cotton” OR “Gossypium”) and “micronutrient” OR “boron” OR “iron” OR “manganese” OR “zinc”, “signaling” OR “transport” OR “homeostasis” OR “deficiency” OR “toxicity” OR “nutrient use efficiency” OR “NUE” OR “yield” OR “fiber quality” OR “gene expression” OR “breeding”.
Additional studies were identified through backward snowballing (reviewing reference lists) and forward citation tracking of seminal articles. Papers were included if they were peer-reviewed primary research articles, review papers, and authoritative book chapters. Studies were included if they directly evaluated the role of B, Fe, Mn, or Zn in cotton growth, physiology, molecular regulation, and agronomic performance. Additional studies investigating molecular mechanisms (transporters, transcription factors, hormonal regulation), nutrient signaling pathways, or breeding strategies for improved micronutrient use efficiency were also included. Mechanistic studies in model plants (e.g., Arabidopsis thaliana (L.) Heynh., rice (Oryza sativa L.), and maize (Zea mays L.)) were incorporated when findings provided transferable insights relevant to cotton micronutrient biology. Non-English publications, studies where micronutrients were not the central focus, or where data lacked micronutrient-specific measurements and research on crops other than cotton unless supported by mechanistic generalizability were excluded.
All retrieved records were screened first by title and abstract to determine topical relevance. Full-text articles meeting preliminary criteria were reviewed in detail for eligibility. Key information was extracted into a structured matrix capturing study objectives, experimental design (field, greenhouse, or molecular laboratory data), cotton species or cultivar, nutrient source, and dosage. Insights on physiological responses, identified genes or proteins, and effects on yield or fiber-related traits were also noted. Extracted evidence was synthesized thematically to align with the objectives of this review. Themes included (a) physiological and phenotypic effects of micronutrient availability, (b) impacts on yield formation and fiber quality, (c) molecular and genetic mechanisms regulating micronutrient uptake and homeostasis, (d) micronutrient signaling and integrative pathways, (e) breeding innovations and technological tools for improving micronutrient use efficiency. A narrative synthesis was used to integrate findings, identify areas of consensus, highlight contradictions, and outline knowledge gaps. Figures and tables were constructed to summarize pathways, gene families, and agronomic outcomes across studies.

3. Effect of B, Fe, Mn, and Zn on Plant Growth and Development

Cotton’s growth phases from seedling, root development, vegetative, and reproductive growth and development are highly sensitive to the availability of all nutrients including micronutrients. The deficiencies in these nutrients often interact to exacerbate plant stress. For example, B deficiency impairs pollen tube growth during flowering, affecting flower fertilization [18]. Similarly, B deficiency interferes with carbohydrate transport and reproductive growth, indirectly affecting the effectiveness of phosphorus and potassium applications [19,20]. Iron deficiency impairs chlorophyll formation, photosynthetic efficiency, and ultimately boll retention [21]. Manganese shortages impair enzyme activity and photosynthetic water-splitting, and susceptibility to oxidative stress [22]. Zn deficiency leads to shortened internodes, stunted growth, smaller leaves, and poor boll development [23]. These micronutrient deficiencies not only reduce crop performance directly but also diminish the efficiency of applied macronutrients such as N and P. For instance, Fe and Zn are essential for nitrate reductase activity and protein synthesis [24], meaning that their absence reduces the efficiency of N fertilization. This assertion is in line with several studies that observed yield reductions when these micronutrients are deficient compared with fertilized plots [25,26,27].

Cotton Physiological Stress Indicators for Micronutrients

Boron plays a crucial role in pollen germination and carbohydrate translocation. These are key processes for reproductive development and assimilate partitioning in cotton [28]. Increased B availability promotes square retention, boll set, and the efficient utilization of N and K, and enhances photosynthetic ability and chlorophyll content through improved nutrient mobilization from leaves to developing bolls [28,29]. Low B levels disrupt cell wall integrity and accelerate square abscission, leading to reduced leaf area and photosynthetic capacity [28,30,31]. As a result, B deficiency commonly manifests as dark banding on petioles (Figure 1). Excessive B can induce toxicity that lowers chlorophyll levels and alters antioxidant enzyme activities [31,32]. Adequate B supplementation, often via foliar application, delays leaf senescence and improves yields by sustaining photosynthetic activity [30,33].
Iron is integral to chlorophyll biosynthesis and electron transport, with deficiencies severely disrupting chloroplast structure and function in cotton [21]. Increased Fe availability supports chlorophyll production and maintains photosynthetic efficiency, promoting leaf expansion and overall plant vigor. Low Fe levels, common in high-pH calcareous soils, accelerate chlorosis through reduced chlorophyll synthesis and impaired photosystem activity, leading to the yellowing of young leaves (Figure 2) and decreased net photosynthetic rates. Adequate Fe supplementation enhances enzyme activities involved in respiration and nitrogen assimilation, ensuring sustained crop development and higher biomass accumulation [7].
Manganese functions as a cofactor in photosynthetic enzymes, particularly in photosystem II, and supports chlorophyll synthesis and nitrogen metabolism in cotton [9,34]. Increased Mn availability promotes chlorophyll content and stomatal conductance, enhancing the net photosynthetic rate and carbohydrate accumulation. Its role extends to stress defense, where manganese superoxide dismutase (MnSOD) mitigates reactive oxygen species damage, while incorporation into metalloproteins supports boll development and overall growth [9,34]. Low Mn levels disrupt oxygen evolution in photosynthesis and reduce enzyme activities such as superoxide dismutase, leading to interveinal chlorosis and accelerated leaf senescence [34]. Excessive Mn can induce toxicity, lowering chlorophyll levels and inhibiting growth [9,35,36]. Manganese deficiency first appears in young leaves and shows as yellowing between veins (Figure 3).
Zinc is essential for enzyme activation in carbon fixation and protein synthesis, playing a key role in photosynthesis and hormone regulation in cotton. Zinc contributes to both metabolic regulation and genetic stability, serving as a cofactor for enzymes such as carbonic anhydrase and alcohol dehydrogenase, which facilitate CO2 fixation and energy metabolism. Increased Zn availability boosts carbonic anhydrase activity and chlorophyll concentration [37]. Critical Zn levels range between 13 and 14 μg/g on a dry weight basis for maximum photosynthetic rates and chlorophyll synthesis [37]. Low Zn levels accelerate chlorophyll degradation and reduce stomatal conductance, disrupting cell proliferation and leading to stunted growth and lower leaf area [38]. Zinc deficiency manifests itself in cotton with yellowish leathery-like leaves turned upwards (Figure 4). Adequate Zn supplementation, particularly in combination with B, enhances antioxidant enzyme activities and improves yields by maintaining a sustained photosynthetic performance [39,40].

4. Molecular Mechanisms of B, Fe, Mn, and Zn Utilization in Cotton

Micronutrients like B, Fe, Mn, and Zn are like tiny sparks that ignite cotton growth, driving higher yields. However, the excessive or poorly managed reliance on micronutrient fertilizers can pose environmental risks, including soil accumulation and toxicity that can disrupt nutrient balances [41]. To grow more cotton with minimal environmental costs while improving micronutrient use efficiency (MUE), the plant’s ability to make the most of these nutrients is critical [42]. While smarter farming practices help, the real game-changer lies in breeding cotton varieties that naturally excel at using these nutrients efficiently [6,43,44]. Over the past 30 years, selective breeding has made great strides in enhancing how cotton plants handle B, Fe, Mn, and Zn [21,45]. Future yield gains will require greater attention to internal nutrient redistribution within the plant.
Under Fe-deficient conditions, Gossypium hirsutum basic Helix–Loop–Helix 121 (GhbHLH121) gene expression is upregulated, indicating that it offers a starting point to understanding cotton’s iron deficiency response [21]. The gene GhbHLH121 forms heterodimers with Gossypium hirsutum basic Helix–Loop–Helix 104 (GhbHLH104) or Gossypium hirsutum basic Helix–Loop–Helix 115 (GhbHLH115), independently activating the downstream expression of the three genes Gossypium hirsutum basic Helix–Loop–Helix 38 (GhbHLH38), Gossypium hirsutum Fe-deficiency Induced Transcription factor (GhFIT), and Gossypium hirsutum POPEYE (GhPYE), as shown in Figure 5.
The downstream transcription factors Gossypium hirsutum Fer-Like Iron Deficiency-Induced Transcription Factor (GhFIT) and Gossypium hirsutum POPEYE (GhPYE) are critical for the plant’s adaptive response. GhFIT functions as a central regulator of iron acquisition. Upon activation by the upstream Gossypium hirsutum basic helix–loop–helix 121 (GhbHLH121) complex, GhFIT promotes the expression of genes involved in rhizosphere acidification, such as proton-pumping adenosine triphosphatases (H+-ATPases), and ferric iron reduction, such as ferric-chelate reductase-like enzymes (FRO-like enzymes), thereby enhancing the solubility and uptake of iron from the soil [21,31]
Furthermore, GhPYE plays a pivotal role in managing internal iron homeostasis under deficiency stress. It orchestrates the remobilization and prioritization of iron within the plant, ensuring that the limited available iron is allocated to essential metabolic processes, thereby mitigating oxidative stress and supporting sustained growth [21]. Therefore, the GhbHLH121-mediated pathway coordinates a two-pronged strategy: GhFIT acts to acquire more iron from the environment, while GhPYE acts to conserve and optimize the use of existing iron reserves. This coordinated response enables adaptation to low iron availability.
When boron levels in the soil are low, cotton plants adjust their boron uptake efficiency (BUE) through root extensions to enhance absorption and fine-tune their internal processes to make better use of what is available. These adaptations to B uptake are driven by active root systems and optimized cellular functions that help maintain a healthy boron balance in the soil systems, especially with varieties bred for high BUE [11,20,43,46,47]. Enzymes such as pectin methylesterases and expansins work together to maintain cell wall integrity, thereby enhancing resistance to lodging [4,43,48]. Boron helps in maintaining cell wall structure and function through its involvement in the cross-linking of rhamnogalacturonan II (RG-II), a process mediated by enzymes such as UDP-glycosyltransferases that strengthen cell wall integrity. Concurrently, xyloglucan endotransglucosylases contribute to cell wall remodeling during growth and development [48,49]. Beyond structural functions, boron also modulates signaling pathways, where reactive oxygen species (ROS) generated by oxidases act as key regulators of developmental processes and stress adaptation in cotton [47,50].
When soils are low in iron, plants actively respond to the deficiency. They release special compounds called phytosiderophores from their roots, which act like chemical “magnets” that bind tightly to iron in the soil. This process makes iron more available, allowing the plant to take it up more efficiently by increasing the activity of iron transporters in the roots [21]. Table 1 summarizes iron uptake strategies in various crops, including upland cotton. The most common strategy is reduction-based, where the plant acidifies the rhizosphere, reducing Fe3+ to Fe2+. The reduced Fe2+ is transported via specific transporters like Iron-Regulated Transporter 1 (IRT1). Cotton, for example, uses genes like GhbHLH121 as elucidated earlier to regulate responses to iron deficiency. Bioinformatics offers a systematic way to uncover the genetic networks that govern iron homeostasis in cotton. By profiling genes affected by iron deficiency as shown in Figure 6, research can pinpoint key regulators of iron signaling and transport, creating opportunities to enhance iron acquisition. Plant mechanisms also incorporate enzyme activity. Enzymes such as ferredoxin and heme oxygenase adjust their activity to sustain iron mobilization and availability, ensuring continued photosynthetic efficiency and growth despite limited supply [44].
For manganese and zinc shortages, cotton plants increase the production of metal tolerance proteins and zinc-regulated transporter protein (ZIP transporters), which act like gatekeepers to regulate the uptake and balance of these nutrients, ensuring the plant thrives despite limited supply [9]. Under deficiency, alkaline phosphatase and zinc finger proteins become central to mobilizing zinc, regulating gene expression, and sustaining DNA replication and protein synthesis processes essential for fiber quality and seed development [24,25,59].

4.1. Efficiency Genes and Hormonal Regulatory Mechanisms of B, Fe, Mn, and Zn in Plants

Boron uptake in plants is primarily mediated by the boron transporter (BOR) and nodulin 26-like intrinsic protein (NIP) families, with functional variation observed among species. In cotton, BOR family gene members have been identified to contribute to B export and tolerance. Specific transporters such as BOR1 and NIP5;1 are directly involved in B uptake, while others regulate B translocation and distribution [7,21,50,60]. Similarly, Fe, Mn, and Zn homeostasis in cotton is mediated by Zinc-Regulated/Iron-Regulated Transporter-Like Proteins (ZIPs) and Natural Resistance-Associated Macrophage Proteins (NRAMPs) [24,61]. In plant species related to cotton, ZIP genes have been identified. A study documented 14, 22, and 18 ZIP genes for Fe, Mn, and Zn transport, respectively, with collinearity analyses highlighting structural and functional conservation among these transporters [24].
Reactive oxygen species (ROS), known as oxygen derived free radical and non-radical species, further regulate micronutrient balance [62,63]. These are major byproducts of cellular activity with endogenous ROS accumulation enhancing tolerance under low micronutrient conditions. However, ROS action in plant pathology needs to be better understood and thus can be utilized in cotton. The action of ROS adds another dimension to adaptive responses to micronutrient stress that include modifications in root morphology, the exudation of organic acids, enhanced membrane and intracellular transport, and the induction of high-affinity transporter genes. These mechanisms facilitate the improved uptake and utilization of micronutrients [60]. In Arabidopsis for example, transcription factors such as FIT and bHLH regulate Fe deficiency when activated by MYB proteins including MYB30 and MYB121 to enhance its distribution in plants [64]. Homologous genes in cotton, including GhbHLH121, GhZIP, and GhNRAMP, have been identified as key regulators of micronutrient acquisition and utilization, underscoring conserved regulatory mechanisms across species [21,51,65].

4.2. Hormonal Regulation of B, Fe, Mn, and Zn

Plant hormones act as master regulators of cotton growth and development. Hormones coordinate diverse physiological responses to environmental and nutritional signals. Among them, auxins, cytokinins (CTKs), abscisic acid (ABA), ethylene (ETH), gibberellins (GAs), brassinosteroids (BRs), jasmonic acid (JAs), salicylic acid (SA), and strigolactones (SL) stand out. These play central roles in mediating cotton’s adaptation to the availability of B, Fe, Mn, and Zn [66,67,68,69,70]. ABA has been shown to regulate Fe-driven lateral root formation, with ABA-dependent signaling pathways promoting root development and enhancing Fe redistribution from roots to shoots in both cotton and model systems like Arabidopsis [68]. CTKs serve as long-distance messengers of nutrient status, relaying Zn and Fe utilization signals via the xylem. Genes such as AtIPT3 and AtIPT5, which govern CTK biosynthesis under Zn and Fe stress in Arabidopsis, appear to function through similar pathways in cotton roots which influence nutrient uptake [69].
The interplay between Fe and GAs has been widely reported, with growth regulator factor 4 (GRF4) identified as a key player in Fe uptake and biomass partitioning. Despite this being reported in rice, comparable functions are proposed for cotton [70]. Brassinosteriod signaling kinase 3 (BSK3), essential for root elongation under Fe deficiency in Arabidopsis, points to potential BR–Fe crosstalk in shaping cotton root architecture under nutrient stress [35,70]. Likewise, the application of ethephon, an ETH-releasing compound, improves Zn utilization efficiency by enhancing enzyme activity linked to Zn metabolism. Peptide hormones such as CEPD1 and CEPD2, which stimulate IRT1 expression and promote Fe uptake in Arabidopsis, may also have analogous functions in cotton nutrient transport. Under B deficiency, SA, ABA, and JA converge on WRKY75, a transcription factor that modulates auxin-mediated lateral root elongation and density, ultimately affecting cell wall stability and root morphology in cotton [66]. In a similar way, excess Mn disrupts IAA balance, accelerating IAA oxidation and altering root development, underscoring the interaction between hormones and micronutrient signaling [9,34,35]. A detailed summary of hormonal pathways is shown in Table 2.

4.3. Signal Integration of B, Fe, Mn, and Zn

While the signaling pathways of these micronutrients have been extensively studied individually, their interactions remain poorly understood [11,41,77]. Emerging evidence indicates that the integration of B, Fe, Mn, and Zn uptake represents an evolutionary adaptation that enables plants to maintain a balanced nutrient profile [36,52]. Significant progress has been achieved in identifying the key regulatory components governing B-Fe-Mn-Zn interactions in model species such as Arabidopsis and rice [77]. Although research in cotton is limited, available molecular insights suggest promising opportunities to enhance boron use efficiency, iron use efficiency (IUE), manganese use efficiency (MUE), and zinc use efficiency (ZUE) [21,24,34,35,78]. Current findings reveal a complex network that integrates B, Fe, Mn, and Zn signaling pathways, offering a clearer understanding of their interdependence (Table 3).

4.4. Signaling Integration of B, Fe, Mn, and Zn in Root Development

Local B supply promotes lateral root elongation [72], while excess Mn induces short, highly branched roots in cotton, altering nutrient uptake [80]. Boron deficiency can have a two-way effect on plant growth. Boron deficiency can either promote or suppress taproot growth. Suppression is linked to blue light-induced Fe redox reactions near roots that generate reactive oxygen species (ROS), particularly under combined B and Fe deficiency in calcareous soils [43,65,81]. Boron–Zn interactions further regulate root nutrient dynamics. Adequate B enhances Mn and Fe accumulation while maintaining balanced Mn/Fe ratios, supporting root health. In contrast, B deficiency upregulates ACS11, increasing ethylene biosynthesis, the auxin-mediated inhibition of root elongation, and ROS production. For example, Zn supplementation, including ZnO nanoparticles, were found to alleviate B toxicity by improving root biomass, reducing ROS, and enhancing Fe and Mn transporter activity [82]. At the molecular level, the Arabidopsis transcription factor (AtNIGT1) has been found to integrate B and Zn signals, with homologs likely functioning in cotton [71,82]. B induces Arabidopsis thaliana Nitrate-Inducible GARP-Type Transcriptional Repressor 1 (AtNIGT1) via BOR1, while Zn deficiency reduces its stability [83]. This dual regulation modulates taproot growth, with AtNIGT1 suppressing taproot elongation under B deficiency but only in the presence of Zn, coordinating with Fe and Mn signals to maintain root structure. The BOR1-AtNIGT1 module thus links B and Zn cues to the downstream regulation of root development [83].

4.5. B-Fe-Mn-Zn Signaling Integration to Regulate Cotton Boll Development

Boron, iron, manganese, and zinc availability plays a pivotal role in boll formation and maturation in cotton by influencing reproductive structures and yield. Adequate boron supply enhances boll weight and reduces boll shedding, while manganese excess can disrupt iron homeostasis. This leads to reduced boll nutrient content, as seen in studies where high Mn/Fe ratios impair fiber quality [11,24,25]. Low-Zn conditions impair boll development by limiting enzyme activities, exacerbating iron and manganese imbalances that affect cell wall integrity in bolls. This is pronounced under calcareous soils where Zn availability is low [11,84].
In cotton, the interaction between B and Zn affects Fe and Mn content in bolls. Boron promotes the transport of Fe and Mn to reproductive tissues, as evidenced by increased boll micronutrient levels under combined B-Zn application [11,80]. Boron deficiency inhibits pollen tube growth and boll setting. However, zinc supplementation has been documented to mitigate this by stabilizing membrane functions and hormone signaling, leading to higher boll retention and seed quality [24]. Transcription factors like GhbHLH121 integrate Fe and Zn signals to regulate boll gene expression under deficiency, coordinating with boron transporters for nutrient allocation and influencing fiber elongation [21,60]. Optimal B-Zn ratios ensure balanced Mn/Fe uptake, preventing oxidative stress in bolls and improving fiber quality, with foliar applications of Zn, Fe, and B significantly boosting boll yield.

4.6. B, Fe, Mn, and Zn Signaling Integration to Regulate Cotton Response to Stress

Boron, iron, manganese, and zinc are integral to cotton’s stress response mechanisms, modulating antioxidant defenses and nutrient homeostasis under abiotic stresses like toxicity or deficiency [4,85,86,87]. Boron toxicity increases reactive oxygen species (ROS) accumulation; however, zinc mitigates this stress by enhancing the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), thereby reducing hydrogen peroxide (H2O2) and malondialdehyde (MDA) levels in both roots and leaves, as demonstrated in cotton seedlings treated with zinc oxide (ZnO) nanoparticles [59,66,88]. Manganese and iron interactions under stress influence redox balance. Excess Mn disrupts Fe uptake and exacerbates oxidative damage, particularly in acidic soils where Mn toxicity is prevalent [35].
In cotton, ZnO nanoparticles have been shown to upregulate ABC transporter genes and photosynthesis pathways to counter boron stress. These genes signal and set in motion processes that lead to nutrient redistribution and stress tolerance [59,85]. Boron interacts with Zn to modulate hormone signaling (e.g., jasmonic acid), enhancing resilience to toxicity, with foliar Zn reducing B-induced growth inhibition. Under calcareous soil conditions, balanced B, Zn, Fe, and Mn ratios improve membrane integrity and reduce susceptibility to environmental cues like salinity. In one study, nano-Zn applications mitigated salt stress by maintaining ionic homeostasis [26]. Heat stress responses are alleviated by micronutrient sprays, including Mn and Zn, which upregulate defense genes and reduce oxidative damage in cotton [89]. More details are elucidated in Table 4.

4.7. B, Fe, Mn, and Zn Signaling Integration Regulating Nutrient Uptake

The AtNIGT1s family (AtNIGT1.1–1.4) plays a central role in nutrient regulation by repressing B-starvation-induced genes (e.g., BOR1, NIP5;1) and controlling Zn-starvation-responsive genes (ZIP2/4, HMA2/4). These set in motion processes that lead to enhanced Zn utilization. AtNIGT1 expression is induced by high B and Zn deficiency and regulated by transcription factors AtbHLH121 and AtMYB13, linking B and Zn signaling pathways [48,76,90]. Boron directly promotes Zn utilization [11,80]. In rice and cotton, the B transporter BOR1 activates Zn-starvation-induced (ZSI) genes by interacting with SPX4-like proteins, leading to SPX4 degradation, MYB translocation into the nucleus, and the induction of Zn-responsive genes [46,65,71]. This BOR1–SPX4–MYB axis exemplifies B–Zn crosstalk, where boron signaling co-activates both B- and Zn-responsive pathways.
The bHLH transcription factors also contribute to B signaling via cytoplasmic–nuclear shuttling [21,60]. Furthermore, SPX4 coordinates MYB13 (Zn signaling) and bHLH121 (B signaling), forming a unified BOR1–SPX4–bHLH121–MYB13 cascade that integrates B and Zn responses [21,60]. BOR1 and SPX4 are regulated through ubiquitination by plasma membrane-localized E3 ubiquitin ligases. Under toxic B conditions, BOR1 is targeted for degradation, preventing excess B accumulation [59,66,88]. This BOR1–SPX module transduces B signals to core transcription factors, enabling the synergistic regulation of B- and Zn-responsive genes [91]. Downstream, MYB, bHLH, and NIGT1 sustain B–Zn homeostasis under fluctuating environments [92].
Beyond Zn, B also influences Mn utilization by regulating Mn concentration and assimilation. Boron reduces free Mn levels by repressing NRAMP1, and activates MTP11, while stimulating Mn superoxide dismutase activity. This demonstrates B’s role in linking Mn and Zn regulation [93]. In cotton, B–Fe–Mn–Zn integration extends to macronutrient uptake. B enhances N and K absorption but reduces P and Fe translocation under high B. Zinc promotes N and K uptake while antagonizing P and Fe and also affects sulfur metabolism through enzyme activation [11,94]. Although the molecular basis of B–Fe–Mn–Zn signaling in cotton remains limited and unclear, evidence from model plants shows that these micronutrients function both independently and interactively, coordinating with macronutrient (N, P, K, S) uptake (Table 5).

5. Recent Approaches for Breeding Nutrient-Efficient Cotton Varieties

The natural variation in micronutrient efficiency among cotton genotypes provides an opportunity to breed varieties with both high yield potential and improved NUE. High-throughput phenotyping, particularly using unmanned aerial vehicles (UAVs) equipped with multispectral and hyperspectral sensors, now enables the precise assessment of chlorophyll content, biomass, and micronutrient status [95]. With these abilities, these technologies allow the detection of nutrient deficiency symptoms [95]. However, cotton’s complex canopy and inconsistent correlations between biomass and yield under variable micronutrient conditions remain a major challenge [1]. Advances in UAV imaging and precision cameras are expected to overcome these limitations, enabling more accurate trait measurement [96,97].
Integrating UAV-based phenotyping with genome-wide association studies (GWAS) facilitates the discovery of genes controlling B, Fe, Mn, and Zn efficiency [95]. Field trials with gradient micronutrient treatments can further improve screening accuracy while conserving resources. Genes such as GhbHLH121 (Fe regulation) and GhZIP3 (Zn uptake) enhance NUE and yield stability under deficiency, while BOR1 and NRAMP1 regulate B and Mn transport [21,60].
Breeding strategies can build on identifying and prioritizing the regulation of such genes into elite cotton lines. For example, the regulation of BOR1 influences B deficiency-related reproductive success, while enhanced IRT1 affects Fe and Zn uptake under calcareous soils [46,65,71,98]. Such targets provide a molecular framework for breeding strategies. Marker-assisted selection (MAS), CRISPR-based editing, and transgenic approaches targeting genes such as GhMTP11 (Mn homeostasis) are producing varieties with balanced micronutrient uptake and improved fiber quality [79]. Lessons from model plants like Arabidopsis and rice continue to inform these efforts (Table 6).

6. Future Research Directions for B, Fe, Mn, and Zn Efficiency in Cotton

The physiology of B, Fe, Mn, and Zn uptake, assimilation signaling, and efficiency in cotton is increasingly receiving attention. However, the genetic, hormonal pathways and technological advances remain underexplored compared with other crops such as corn and soybeans. Insights from corn, soybeans, and other plants highlight that there is a potential to improve cotton’s NUE and yield stability. Future research should focus on high-throughput phenotyping using UAV-based imaging, combined with genome-wide association studies (GWAS), among other molecular techniques for identifying nutrient-efficient genotypes. Breeding strategies incorporating marker-assisted selection and CRISPR editing, for instance, overexpressing BOR1 or IRT1, or editing GhMTP11, can enhance micronutrient uptake, fiber quality, and stress tolerance. Research focusing on nutrient interactions with macronutrients (N, P, K, S), adaptation to environmental stresses, and sustainable nutrient management is highly recommended. Integrating genetic improvements with precision fertilization, biofortification, and sensor-guided application can optimize nutrient efficiency, reduce environmental impact, and support high-yield, resilient cotton production

7. Conclusions

In conclusion, this review synthesizes the pivotal roles of boron, iron, manganese, and zinc in cotton physiology, signaling integration, and nutrient use efficiency. It also addresses yield gaps often overlooked in macronutrient-focused programs. The key findings demonstrate that these micronutrients regulate photosynthesis, hormone signaling, stress tolerance, and reproductive success. In most cases, micronutrient deficiencies are exacerbated by soil pH and interplant nutrient interactions. On a molecular level, genes such as BOR1, IRT1, and GhZIP3 provide targets for optimization. Looking ahead, a systems approach integrating advances in microRNA research, CRISPR-based gene editing, UAV phenotyping, and precision nutrition offer promising pathways to enhance micronutrient use efficiency, mitigate environmental challenges, and sustain high-yield cotton production.

Author Contributions

Conceptualization: U.A., A.H., D.N.Y., S.K., and F.A.; methodology: U.A. and D.N.Y.; software: U.A. and D.N.Y.; validation: U.A., A.H., and F.A.; formal synthesis: U.A., A.H., D.N.Y., S.K., and F.A.; investigation: U.A., A.H., D.N.Y., S.K., and F.A.; resources, U.A. and D.N.Y.; data curation, U.A., A.H., and D.N.Y.; writing—original draft preparation: U.A., D.N.Y., and S.K.; writing—review and editing: U.A., D.N.Y., A.H., and F.A.; supervision: U.A. and D.N.Y.; project administration: U.A. and D.N.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

All data for this article is contained within it. For additional information, please contact the corresponding author.

Acknowledgments

During the preparation of this manuscript, the author(s) took full responsibility for the content of this publication.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

NUENutrient Use Efficiency
BUEBoron Use Efficiency
IUEIron Use Efficiency
MUEManganese Use Efficiency
ZUEZinc Use Efficiency
N, P, K, SNitrogen, Phosphorus, Potassium, Sulfur
IRT1Iron-Regulated Transporter 1
BOR1Boron Transporter 1
NIP5;1Nodulin 26-like Intrinsic Protein 5;1
ZIPZinc/Iron-Regulated Transporter-like Protein family
NRAMP1Natural Resistance-Associated Macrophage Protein 1
MTP11Metal Tolerance Protein 11
HMA2/HMA4Heavy Metal ATPase 2/4
GhbHLH121Basic Helix–Loop–Helix transcription factor in cotton
GhZIP3Zinc Transporter gene in cotton
GhMTP11Cotton Metal Tolerance Protein gene
miRNAsMicroRNAs
miR169, miR398, miR408Specific microRNAs involved in nutrient regulation
NFYANuclear Factor Y subunit A
ROSReactive Oxygen Species
RG-IIRhamnogalacturonan II
SODSuperoxide Dismutase
PODPeroxidase
CATCatalase
ABAAbscisic Acid
CTK/CTKsCytokinins
ETHEthylene
GA/GAsGibberellins
BR/BRsBrassinosteroids
JA/JAsJasmonic Acid
SASalicylic Acid
SLStrigolactones
IAAIndole-3-Acetic Acid (Auxin)
UAVsUnmanned Aerial Vehicles
scRNA-seqSingle-Cell RNA Sequencing
GWASGenome-Wide Association Studies
MASMarker-Assisted Selection
CRISPRClustered Regularly Interspaced Short Palindromic Repeats

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Figure 1. Deficiency symptoms of boron in cotton seedlings. Adapted from Bayer Crop Sciences.
Figure 1. Deficiency symptoms of boron in cotton seedlings. Adapted from Bayer Crop Sciences.
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Figure 2. Iron deficiency symptoms showing stunted and yellowing of leaf lamina. Source: Texas A&M AgriLife and Extension.
Figure 2. Iron deficiency symptoms showing stunted and yellowing of leaf lamina. Source: Texas A&M AgriLife and Extension.
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Figure 3. Visible symptoms of manganese deficiency in leaves. Source: University of Florida.
Figure 3. Visible symptoms of manganese deficiency in leaves. Source: University of Florida.
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Figure 4. Visible symptoms of Zn deficiency in cotton seedlings. Image adapted from Bayer Crop Sciences.
Figure 4. Visible symptoms of Zn deficiency in cotton seedlings. Image adapted from Bayer Crop Sciences.
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Figure 5. A working model of GhbHLH121-mediated regulation under iron deficiency in cotton demonstrating the upstream and downstream regulation of genes under various Fe soil conditions was demonstrated by Li, et al. [21].
Figure 5. A working model of GhbHLH121-mediated regulation under iron deficiency in cotton demonstrating the upstream and downstream regulation of genes under various Fe soil conditions was demonstrated by Li, et al. [21].
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Figure 6. A potential bioinformatic tool that can be used to profile genetic expression. Iron deficiency reduces the expression of photosynthesis genes in cotton leaves. R.E.L stands for Relative Expression Level. ** indicates statistical significance at p ≤ 0.05 (95% confidence level), while * indicates marginal significance at p ≤ 0.10 (90% confidence level). Reproduced with permission from [21].
Figure 6. A potential bioinformatic tool that can be used to profile genetic expression. Iron deficiency reduces the expression of photosynthesis genes in cotton leaves. R.E.L stands for Relative Expression Level. ** indicates statistical significance at p ≤ 0.05 (95% confidence level), while * indicates marginal significance at p ≤ 0.10 (90% confidence level). Reproduced with permission from [21].
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Table 1. Strategies and key mechanisms of iron uptake in model crops, including cotton.
Table 1. Strategies and key mechanisms of iron uptake in model crops, including cotton.
CropStrategyHow It WorksKey Enzymes/Hormones/PathwaysReference
Arabidopsis thaliana (L.) HeynhReductionMediates proton release, reduces Fe3+ to Fe2+, and transports Fe2+ into roots.FRO2, IRT1 (transporter); FIT, PYE, BTS pathways; auxin and ethylene hormones enhance gene expression.[51,52]
Rice (Oryza sativa (L.)ChelationSecretes phytosiderophores to chelate, Fe3+, forming complexes transported into roots.Phytosiderophores (e.g., mugineic acid), YSL transporters; OsIRO2 and OsIDEF1 regulate responses.[53,54]
CottonReductionResponds to deficiency by reducing Fe3+ at root surface and uptaking Fe2+; involves rhizosphere acidification and gene upregulation for homeostasis.GhbHLH121 (transcription factor), FRO-like reductases, IRT-like transporters; FIT-like and bHLH pathways; reactive oxygen species signaling.[21,55,56]
BarleyChelationPrefers chelation but can show hybrid responses; secretes phytosiderophores to mobilize Fe3+.HvYS1 (transporter), phytosiderophores; IDEF1/2 transcription factors regulate under deficiency.[57]
MaizeChelation under high pH soilsReleases mugineic acid family phytosiderophores (MA’s) to bind and uptake Fe3+ complexes.ZmYS1 (transporter), DMA (deoxymugineic acid); bHLH and NAC transcription factors in response pathways.[53,54,58]
Acronyms: FRO2: Ferric Reduction Oxidase 2, IRT1: Iron-Regulated Transporter 1; FIT: FE-deficiency Induced Transcription factor, PYE: POPEYE, BTS: BRUTUS, YSL: Yellow Stripe-Like transporters; OsIRO2: Oryza sativa Iron-Related Transcription factor 2; OsIDEF1: Oryza sativa Iron Deficiency-responsive Element-binding Factor 1, FRO-like: Ferric Reduction Oxidase-like reductases, IRT-like: Iron-Regulated Transporter-like; bHLH: basic Helix–Loop–Helix; HvYS1: Hordeum vulgare Yellow Stripe 1, IDEF1/2: Iron Deficiency-responsive Element-binding Factor 1/2, ZmYS1: Zea mays Yellow Stripe 1, and DMA: deoxymugineic acid.
Table 2. Key genes and hormonal pathways regulating B, Fe, Mn, and Zn uptake and utilization in cotton and model plants.
Table 2. Key genes and hormonal pathways regulating B, Fe, Mn, and Zn uptake and utilization in cotton and model plants.
NutrientGeneHormonePathway ControlledPlantReferences
BBOR1Auxin (IAA)Root development and B uptake; regulates B transport under deficiency, interacting with auxin signaling for cell wall integrityArabidopsis (Arabidopsis thaliana (L.) Heynh), Cotton[71,72]
BNIP5;1ABA, JAStress response and embryogenesis; B deficiency triggers ABA-mediated stress pathways for somatic embryogenesisArabidopsis[72,73]
FeIRT1Ethylene, ABAFe uptake and homeostasis; ethylene upregulates IRT1 expression under Fe deficiency, ABA promotes reutilizationArabidopsis, Rice (Oryza sativa L.), Cotton[73,74]
FeFIT (FER-like)Auxin, BRTranscriptional regulation of Fe acquisition; auxin and BR coordinate root elongation and Fe transporter activationArabidopsis, Cotton[73,74]
FeGhbHLH121GAFe deficiency response regulates upstream Fe uptake genes like FIT in response to GA signalingCotton[21]
MnNRAMP1IAAMn homeostasis and toxicity response; Mn excess disrupts IAA oxidation, affecting root growthArabidopsis, Cotton[61,75]
ZnZIP family (e.g., ZIP2, ZIP4)AuxinZn uptake and hormone biosynthesis; Zn regulates auxin production for root branching and cell elongationArabidopsis, Cotton[24]
ZnHMA2/HMA4ABAZn transport and stress tolerance; ABA-mediated membrane stability under Zn deficiencyArabidopsis[76]
ZnGhZIP3CTKZn signaling from roots to shoots; CTK biosynthesis influences Zn utilizationCotton
Table 3. Key transport mechanisms and interactions of B, Fe, Mn, and Zn in plants.
Table 3. Key transport mechanisms and interactions of B, Fe, Mn, and Zn in plants.
Nutrient InteractionKey Components/SignalsPlantReferences
B-ZnB transporters (BOR1/NIP5;1) interact with Zn transporters (ZIP family), affecting metabolic processes and uptake of other nutrients like Cu, Fe, MnArabidopsis, Cotton[76]
Fe-ZnShared Transporters (IRT1, ZIP2/4); FIT transcription factor regulates Fe acquisition with Zn crosstalk; SPX proteins mediate homeostasisArabidopsis, Rice (Oryza sativa L.)[35,70,79]
Fe-MnNRAMP transporters (NRAMP1); Crosstalk in redox homeostasis and toxicity response; MTP11 involved in Mn transport influenced by Fe signalsArabidopsis, Rice (Oryza sativa L.)[35,70]
Zn-MnHMA2/HMA4 transporters; Interaction in stress tolerance and uptake; Overlap in gene regulatory networks (GRNs) under deficiencyArabidopsis, Sorghum[76]
B-FeBOR1 and IRT1 interaction; Crosstalk in cell wall integrity and Fe deficiency responseArabidopsis[71]
Multi (Fe-Zn-Mn-Cu)bHLH transcription factors (e.g., GhbHLH121); Crosstalk via ubiquitin ligases and redox signalsCotton, Arabidopsis[21,56,64]
Table 4. Integrated roles of boron, iron, manganese, and zinc signaling in regulating gene expression and stress responses in cotton and related crops.
Table 4. Integrated roles of boron, iron, manganese, and zinc signaling in regulating gene expression and stress responses in cotton and related crops.
NutrientGeneEnvironmental ChangeResponsePlantReferences
BBOR1/Bot1 orthologBoron deficiency/toxicityInhibits root cell elongation via ethylene/auxin/ROS pathway; upregulates transporters for toleranceArabidopsis thaliana (L.) Heynh[4,82]
BACS11Low boron availabilityUpregulates ethylene biosynthesis, reducing root growth and increasing ROSTomatoes (Solanum lycopersicum L.), Cotton[43,85]
ZnZIP family (e.g., ZIP transporters)Zinc deficiency under salinity, and toxicityEnhances Zn uptake, stabilizes membranes, mitigates B toxicity by reducing ROSCotton[59,85]
FeIRT1/FIT homologsIron deficiency with high MnCoordinates Fe acquisition, prevents Mn-induced oxidative stress in roots and bollsCotton, Arabidopsis
MnNRAMP1/MTP11Manganese excess/toxicityRegulates Mn transport and sequestration, disrupts Fe homeostasis leading to reduced boll developmentPeanuts (Arachis hypogaea L.), Stylosanthes, Soybean (Glycine max (L.) Merr)[35,36,79]
B-ZnABC transportersBoron toxicity with Zn supplementationUpregulates nutrient redistribution, enhances antioxidant enzymes (SOD, POD, CAT) for stress toleranceCotton[59]
Fe-MnGhbHLH121Combined Fe-Mn deficiency in bollsIntegrates signals for fiber quality, regulates cell wall genes under nutrient stressCotton[12,59]
B-FeCell wall-related genes (e.g., expansins)Boron deficiency in rootsDownregulates expression, impairs root elongation and boll cell integrityCotton, Arabidopsis[12,47]
Acronyms: SOD: superoxide dismutase, POD: peroxidase (commonly guaiacol peroxidase in plant studies), CAT: catalase.
Table 5. Interactions of boron, iron, manganese, and zinc for macronutrient uptake.
Table 5. Interactions of boron, iron, manganese, and zinc for macronutrient uptake.
MicronutrientMacronutrient InfluencedGrowth and Yield TraitKey FindingsReference
BN, P, K, SVegetation, Flowering, Pods, Fiber QualityB enhances N and P metabolism, promotes K translocation; deficiency reduces pod set and fiber strength by disrupting S-involved enzymes.[4,11,29]
FeN, P, K, SVegetation, Nodes, Fiber QualityFe deficiency antagonizes P uptake, reduces N assimilation; impacts node development and fiber maturity via redox effects on S.[25,29,33]
MnN, P, K, SVegetation, Pods, Pod Abortion, Fiber QualityMn synergizes with K for vegetation growth; excess antagonizes Fe and P, increasing pod abortion and reducing fiber quality via S oxidation imbalance.[34,35,36,75,78,89]
ZnN, P, K, SFlowering, Nodes, Pods, Pod Abortion, Fiber QualityZn positively interacts with N and K for flowering and node formation; antagonizes P, reducing pod abortion; enhances fiber quality by improving S metabolism.[11,26,37,55,84,85]
Table 6. Key genes regulating boron, iron, manganese, and zinc use efficiency.
Table 6. Key genes regulating boron, iron, manganese, and zinc use efficiency.
NutrientGene ExampleInfluence on Nutrient Use EfficiencyReferences
BBOR1 transporters and miR408 genesEnhances boron uptake under B deficient soils, reduces pod abortion, and improves cell wall integrity under deficiency; critical for reproductive growth.[88,98]
BNIP5;1Facilitates B transport under low B conditions, improving root and boll development; enhances BUE.[99]
Nutrients PIP1;1, PIP2;1, PIP2;2Enhances nutrient uptake and stress tolerance traits of cotton.[86]
FeIRT1Improves Fe uptake in calcareous soils, reduces chlorosis, and enhances N and P assimilation for better vegetation and fiber quality.[100]
FeGhbHLH121Regulates Fe deficiency responses, enhances Fe and Zn homeostasis, improving boll development and yield stability.[101]
MnNRAMP1Controls Mn uptake and homeostasis, prevents toxicity, and supports K and S metabolism for pod retention.[102]
MnGhMTP11Enhances Mn sequestration, reduces oxidative stress, and improves pod and fiber quality under Mn excess.[102]
ZnGhZIP3Boosts Zn uptake and signaling, improves N and K assimilation, reduces pod abortion, and enhances fiber length.[63]
ZnHMA4Facilitates Zn transport, enhances stress tolerance, and supports S metabolism for improved flowering and node formation.[76]
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Arinaitwe, U.; Yabwalo, D.N.; Hangamaisho, A.; Kwikiiriza, S.; Akitwine, F. Advances in Boron, Iron, Manganese, and Zinc Signaling, Transport, and Functional Integration for Enhancing Cotton Nutrient Efficiency and Yield—A Review. Int. J. Plant Biol. 2026, 17, 7. https://doi.org/10.3390/ijpb17010007

AMA Style

Arinaitwe U, Yabwalo DN, Hangamaisho A, Kwikiiriza S, Akitwine F. Advances in Boron, Iron, Manganese, and Zinc Signaling, Transport, and Functional Integration for Enhancing Cotton Nutrient Efficiency and Yield—A Review. International Journal of Plant Biology. 2026; 17(1):7. https://doi.org/10.3390/ijpb17010007

Chicago/Turabian Style

Arinaitwe, Unius, Dalitso Noble Yabwalo, Abraham Hangamaisho, Shillah Kwikiiriza, and Francis Akitwine. 2026. "Advances in Boron, Iron, Manganese, and Zinc Signaling, Transport, and Functional Integration for Enhancing Cotton Nutrient Efficiency and Yield—A Review" International Journal of Plant Biology 17, no. 1: 7. https://doi.org/10.3390/ijpb17010007

APA Style

Arinaitwe, U., Yabwalo, D. N., Hangamaisho, A., Kwikiiriza, S., & Akitwine, F. (2026). Advances in Boron, Iron, Manganese, and Zinc Signaling, Transport, and Functional Integration for Enhancing Cotton Nutrient Efficiency and Yield—A Review. International Journal of Plant Biology, 17(1), 7. https://doi.org/10.3390/ijpb17010007

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