What Can Boron Deficiency Symptoms Tell Us about Its Function and Regulation?

Kiwifruit sensitivity to boron: impact on physiological and molecular responses

Boron (B) is an essential micronutrient critical for crop growth and productivity. However, excessive boron concentrations can impair plant development, and detoxification remains a significant challenge. Understanding genetic variability and identifying tolerance mechanisms are crucial for developing boron-resistant cultivars. This study explores the physiological and molecular responses of two Actinidia species, namely kiwifruit (A.chinensis) and kiwiberry (A.arguta), to varying levels of excess B. Under excessive B conditions, B accumulation followed the order roots< stems< leaves, with maximum concentrations of 68.6 mg/kg, 105 mg/kg, and 160.7 mg/kg in AC, and 68.2 mg/kg, 107 mg/kg, and 196.9 mg/kg in AA, respectively. B toxicity symptoms appeared in AA when B levels exceeded 50 mg/kg, leading to a 15-20% reduction in dry weight across roots, stems, and leaves. AC exhibited greater sensitivity, with a 20-30% reduction in dry biomass. Both species showed significant declines in chlorophyll a and b content under B stress, with alterations in the chlorophyll a/b ratio and increased oxidative stress. Additionally, stress-responsive genes, including 1-aminocyclopropane-1-carboxylate synthase (Actinidia10066) and xyloglucan endotransglucosylase/hydrolase (Actinidia11948), were downregulated in response to B stress, suggesting potential disruptions in growth and development. These findings provide valuable insights into the differential physiological and molecular responses to excess boron in Actinidia species, laying a foundation for functional genomics research and the development of boron-tolerant kiwifruit cultivars.

Bridging Molecular Insights and Agronomic Innovations: Cutting-Edge Strategies for Overcoming Boron Deficiency in Sustainable Rapeseed Cultivation

Boron (B) is an essential micronutrient for the growth, development, and maintenance of cellular integrity in vascular plants, and is especially important in cell wall synthesis and reproductive development. Rapeseed (Brassica napus L.), one of the dominant oil crops globally, has a high boron demand and its yield is dramatically decreased under B-deficiency conditions. Rapeseed, which is very sensitive to boron deficiency, suffers from reduced growth and reproductive development, ultimately causing severe yield losses. Here, we reviewed the present state of knowledge on the physiological function of boron in rapeseed, mechanisms of boron uptake and transport, specific effects of boron deficiency in rapeseed, and approaches to alleviate boron deficiency in rapeseed at the agronomical and molecular levels. A specific focus is given to recent molecular breakthroughs and agronomic approaches that may improve boron efficiency. The review focuses on practices that may alleviate the problems caused by boron-deficient soils by investigating the genetic and physiological mechanisms of boron tolerance. In summary, this review describes the integration of molecular information with practical agronomy as an important aspect of breeding future nutrient-efficient rapeseed cultivars that can sustain increasing yields while being cultivated in regions with boron-deficient soils.

Transcriptional Analysis Reveals the Differences in Response of Floral Buds to Boron Deficiency Between Two Contrasting Brassica napus Varieties

Boron (B) is an essential micronutrient for the development of crops, and its reproductive stage is particularly sensitive to B deficiency. Brassica napus L., as an important oil-crop species, is extremely vulnerable to B deficiency. The typical B-deficient symptom of "flowering without seed setting" usually results in severe yield loss. However, few studies have focused on the response of the reproductive organs to B deficiency. In this study, the B-efficient variety "Zhongshuang 11" (ZS11) and the B-inefficient variety "Westar 10" (W10) of Brassica napus were selected to be cultivated at the developmental stage (BBCH15) in a pot experiment, both with and without B supply. Clear phenotype differences in B deficiency between the two varieties' flowers appeared only at the reproductive stage, and only W10 showed symptoms of delayed flower opening, stigma exsertion, and resulted in abortion. Transcriptome analysis for the early buds of both varieties between B supply (+B) and free (-B) treatments revealed that W10 had more differentially expressed genes (DEGs) corresponding to its greater susceptibility to -B. As two potential mechanisms to improve B-efficient utilization, we focused on analyzing the expression profiles of B transporter-related genes and phytohormone metabolism-related genes. BnaC05.NIP7;1, BnaC08.NIP3;1, and BnaBOR2s were identified as the key genes which could enhance the capacity of B translocation to buds of ZS11. Additionally, combined with a phytohormone concentration measurement, we showed that a significant increase in IAA and a drastic decrease in JA could predominantly lead to the abnormal development of W10's buds. BnaC02.NIT2 (Nitrilase 2) and BnaKAT5s (3-Ketoacyl-CoA Thiolase 5), which are IAA and JA biosynthesis genes, respectively, could be the key genes responsible for the changes in IAA and JA concentrations in W10's buds under -B. These candidate genes may regulate the genotype differences in the response of the rapeseed reproductive stage to -B between different B-efficient varieties. It also has potential to breed rapeseed varieties with B-efficient utilization in the reproductive stage, which would improve the seed yield under -B condition.

Transcriptome and phytohormone profiling of stamen and pistil in Brassica napus under boron deficiency

Plant reproduction is a fundamental requirement for plants to sustain genetic inheritance. In the perspective of plant nutrition, such process is strongly influenced by boron deficiency (-B) and as documented about a century ago. To date, little is known about the mechanism of boron deficiency-induced fertility reduction. In this study, we successfully established a cultivation system for Brassica napus to precisely manipulate boron supply when the generative stage initiates. We dissected the stamen and pistil of early-developing Brassica napus flower buds for transcriptome and phytohormone analysis, and demonstrated pistil and stamen showed distinct responding processes to -B. In addition, we revealed that auxin (IAA)-related compounds and several IAA-biosynthesis genes may play important roles in reproductive organ responding to -B, suggesting the IAA metabolism pathway seems to play a crucial role in -B induced reproductive organ abortion process. Taken together, we created a reliable system to study boron deficiency induced fertility reduction, by which generated the first transcriptome result for dissected stamen and pistil under different boron regimes, and suggested IAA metabolism pathway deserves as important target for further study in such regimes.

Plant nutrition challenges for a sustainable agriculture of the future

This article offers a comprehensive review of sustainable plant nutrition concepts, examining a multitude of cutting-edge techniques that are revolutionizing the modern area. The review copes with the crucial role of biostimulants as products that stimulate plant nutrition processes, including their potential for biofertilization, followed by an exploration of the significance of micronutrients in plant health and growth. We then delve into strategies for enhancing plants' tolerance to mineral nutrient contaminants and the promising realm of biofortification to increase the essential nutrients necessary for human health. Furthermore, this work also provides a concise overview of the burgeoning field of nanotechnologies in fertilization, while the integration of circular economy principles underscores the importance of sustainable resource management. Then, with examined the interrelation between micronutrients. We conclude with the future challenges and opportunities that lie ahead in the pursuit of more sustainable and resilient plant systems.

Boron toxicity in plants: understanding mechanisms and developing coping strategies; a review

KEY MESSAGE

Boron is essential for plants, but excess can induce toxicity. Boron (B) is a vital micronutrient for plants, but excess B can induce toxicity symptoms and reduce crop yields. B bioavailability depends on soil properties, including clay type, pH, and organic matter content. Symptoms of B toxicity include reduced shoot and root growth, leaf chlorosis and necrosis, impaired photosynthesis, and disrupted pollen development. This review paper examines the current knowledge on B toxicity mechanisms, tolerance strategies, and management approaches in plants. This review covers (1) factors affecting B bioavailability; (2) toxicity symptoms in plants; (3) uptake, transport, and detoxification mechanisms; and (4) strategies. To mitigate toxicity, plants reduce B uptake, activate efflux transporters, compartmentalize B, and enhance antioxidant systems. On the basis of this review, future research should focus on identifying novel tolerance mechanisms, exploring genetic strategies for improved B management, and developing innovative agronomic interventions. These insights will facilitate the breeding and management of crops for enhanced productivity under B toxicity stress.

Plant Growth Regulation in Cell and Tissue Culture In Vitro

Precise knowledge of all aspects controlling plant tissue culture and in vitro plant regeneration is crucial for plant biotechnologists and their correlated industry, as there is increasing demand for this scientific knowledge, resulting in more productive and resilient plants in the field. However, the development and application of cell and tissue culture techniques are usually based on empirical studies, although some data-driven models are available. Overall, the success of plant tissue culture is dependent on several factors such as available nutrients, endogenous auxin synthesis, organic compounds, and environment conditions. In this review, the most important aspects are described one by one, with some practical recommendations based on basic research in plant physiology and sharing our practical experience from over 20 years of research in this field. The main aim is to help new plant biotechnologists and increase the impact of the plant tissue culture industry worldwide.

Duckweed pectic-arabinogalactan-proteins can crosslink through borate diester bonds

Material containing pectin and arabinogalactan-protein (AGP) was released and purified from Spirodela alcohol insoluble residues. Results of carbohydrate analyses and two-dimensional NMR spectroscopy suggest that this material is composed of apiogalacturonan and rhamnogalacturonan-I covalently attached to AGPs. 11B NMR spectroscopy indicated that some of the glycoses in this complex exist as their boric acid monoesters. Borate diesters were formed when the pectic-AGPs were allowed to react at pH above 6.2 with the boron-depleted pectic-AGPs, suggesting that in vitro two pectic-AGP molecules can crosslink to one another through borate. Borate diesters also formed when the pectic-AGPs were incubated with monomeric rhamnogalacturonan-II in the presence of Pb2+ ion at pH 9.2. This data presents evidence of the first wall polymer after rhamnogalacturonan-II to crosslink through borate diesters. We suggest that the formation of these borate-crosslinks may help Spirodela respond to high-pH condition.

Physiological and molecular mechanisms of Acacia melanoxylon stem in response to boron deficiency

Boron is an essential micronutrient for plant growth as it participates in cell wall integrity. The growth and development of Acacia melanoxylon stem can be adversely affected by a lack of boron. To explore the mechanism of boron deficiency in A. melanoxylon stem, the changes in morphological attributes, physiological, endogenous hormone levels, and the cell structure and component contents were examined. In addition, the molecular mechanism of shortened internodes resulting from boron deficiency was elucidated through transcriptome analysis. The results showed that boron deficiency resulted in decreased height, shortened internodes, and reduced root length and surface area, corresponding with decreased boron content in the roots, stems, and leaves of A. melanoxylon. In shortened internodes of stems, oxidative damage, and disordered hormone homeostasis were induced, the cell wall was thickened, hemicellulose and water-soluble pectin contents decreased, while the cellulose content increased under boron deficiency. Furthermore, plenty of genes associated with cell wall metabolism and structural components, including GAUTs, CESAs, IRXs, EXPs, TBLs, and XTHs were downregulated under boron deficiency. Alterations of gene expression in hormone signaling pathways comprising IAA, GA, CTK, ET, ABA, and JA were observed under boron deficiency. TFs, homologous to HD1s, NAC10, NAC73, MYB46s, MYB58, and ERF92s were found to interact with genes related to cell wall metabolism, and the structural components were identified. We established a regulatory mechanism network of boron deficiency-induced shortened internodes in A. melanoxylon based on the above results. This research provides a theoretical basis for understanding the response mechanism of woody plants to boron deficiency.

B2 O3 nanoparticles alleviate salt stress in maize leaf growth zones by enhancing photosynthesis and maintaining mineral and redox status

Salt stress induces significant loss in crop yield worldwide. Although the growth-stimulating effects of micronutrient nanoparticles (NPs) application under salinity have been studied, the molecular and biochemical mechanisms underlying these effects are poorly understood. The large size of maize leaf growth zones provides an ideal model system to sample and investigate the molecular and physiological bases of growth at subzonal resolution. Using kinematic analysis, our study indicated that salinity at 150 mM inhibited maize leaf growth by decreasing cell division and expansion in the meristem and elongation zones. Consistently, salinity downregulated cell cycle gene expression (wee1, mcm4, and cyclin-B2-4). B2 O3 NP (BNP) mitigated the stress-induced growth inhibition by reducing the decrease in cell division and expansion. BNP also enhanced the photosynthesis-related parameters. Simultaneously, chlorophyll, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase/oxygenase were stimulated in the mature zone. Concomitant with growth stimulation by BNP, mineral homeostasis, particularly for B and Ca, was monitored. BNP reduced oxidative stress (e.g., lessened H2 O2 generation along the leaf zones and reduced lipid peroxidation in the mature zone) induced by salinity. This resulted from better maintenance of the redox status, that is, increased the glutathione-ascorbate cycle in the meristem and elongation zones, and flavonoids and tocopherol levels in the mature zone. Our study has important implications for assessing the salinity stress impact mitigated by BNP on maize growth, providing a basis to improve the resilience of crop species under salinity stress conditions.

Role of ABA in the adaptive response of Arabidopsis plants to long-term boron toxicity treatment

Boron (B) toxicity causes impairments in several plant metabolic and physiological processes. Under conditions of excessive B availability, this micronutrient is passively transported through the transpiration stream and accumulates in leaves, causing the development of necrotic regions in leaf tips. Some plants have developed adaptive mechanisms to minimize the toxic effects of excessive B accumulation in their tissues. Thus, for instance, in Arabidopsis it has been described an ABA-dependent decrease in the transpiration rate that would restrict B accumulation in aerial plant tissues in response to short-term B toxicity, this effect being mediated by AtNCED3 (which encodes a key enzyme for ABA biosynthesis). The present work aimed to study the possible involvement of ABA in the adjustment of plant water balance and B homeostasis during the adaptive response of Arabidopsis to prolonged B toxicity. For this purpose, Arabidopsis wild-type and the ABA-deficient nced3-2 mutant plants were subjected to B toxicity for 7 days. We show that ABA-dependent stomatal closure is determinant for the adjustment of plant water relations under conditions of prolonged B toxicity. Results suggest that, in addition to the AtNCED3 gene, the AtNCED5 gene could also be involved in this ABA-dependent stomatal closure. Finally, our results also indicate the possible role of endogenous root ABA content in the mechanism of active efflux of B via BOR4 (efflux-type B transporter) from the root to the external environment under excess B conditions.