Boron Toxicity Research Articles

Interactive effects of gibberellic acid and NPK on morpho-physio-biochemical traits and organic acid exudation pattern in coriander (Coriandrum sativum L.) grown in soil artificially spiked with boron

It was aimed to examine the role of gibberellic acid (GA3) and NPK fertilizer in alleviating boron (B) toxicity in coriander (Coriandrum sativum L.) plants. Two weeks old C. sativum seedlings were subjected to different NPK fertilizers [low NPK (30 kg ha−1) and normal NPK (60 kg ha−1)], which were also supplied by GA3 (50 mg L−1), under varying levels of B i.e., 0, 200 and 400 mg kg−1 in the soil. Results revealed that B toxicity led to a substantial decreased in the plant growth and biomass, photosynthetic pigments, gas exchange characteristics, sugars and essential nutrients in the roots and shoots of C. sativum seedlings. However, B toxicity boosted the production of reactive oxygen species (ROS) by increasing the contents of malondialdehyde (MDA), which is the indication of oxidative stress in C. sativum seedlings and was also manifested by hydrogen peroxide (H2O2) contents and electrolyte leakage (EL) to the membrane bounded organelles. Although, activities of various antioxidative enzymes like superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT) and ascorbate peroxidase (APX), non-enzymatic antioxidants like phenolic, flavonoid, ascorbic acid and anthocyanin contents and organic acids from the roots such as oxalic acid, malic acid, formic acid, citric acid, acetic acid and fumaric acid contents were increased with the increasing levels of B in the soil. The application if NPK and GA3 mitigated B toxicity by stimulated plant growth and biomass, photosynthetic efficiency, nutritional status and antioxidant machinery of the plant by decreasing MDA contents, H2O2 initiation and EL (%) in the roots and leaves of C. sativum seedlings. In addition, the application of NPK and GA3 further decreased the organic acids exudation contents in the roots C. sativum seedlings. Research findings, therefore, suggested that NPK and GA3 application can ameliorate B toxicity in C. sativum seedlings and resulted in improved plant growth and composition under B stress as depicted by balanced contents of organic acids.

Foliar application of silica sol alleviates boron toxicity in rice (Oryza sativa) seedlings

Boron (B) toxicity is one of the limiting factors affecting plant growth. Previous studies showed that silicon (Si) application could alleviate B toxicity. However, there is limited information on how Si alleviates B toxicity in rice, particularly nano-silicon (SiNP). Therefore, the current study aimed to explore the foliar function of SiNP in the reduction of B toxicity in rice. The results showed that B toxicity significantly hampered root and shoot development. However, SiNP application increased root and shoot lengths by 14.29% and 29.67%, respectively, compared to B toxicity treatment. Moreover, SiNP increased fresh weight (FW) of root (28.02%) and shoot (34%) and enhanced dry weight (DW) of root (65.13%), and shoot (26.87%), compared to B toxicity treatment. The application of SiNP decreased the translocation of B to leaves and promoted B adsorption to leaf cell wall. In roots, SiNP triggered high B accumulation and Fourier infrared spectroscopy (FTIR) also suggested higher peak values of functional groups (pectin), indicating that cell wall polysaccharides can adsorb high concentration of B. Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) investigations showed that SiNP treated roots had a well-arranged structure of alkali-soluble pectin (ASP), and ultrastructure of root was well organized. Cell wall adsorbed more than 80% of total B. All of these results suggest that SiNP can alleviate B toxicity in rice seedlings.

Transcriptome profiles reveal the protective role of seed coating with zinc against boron toxicity in maize (Zea mays L.)

Despite its low abundance during biological growth, excessive boron (B) is potentially toxic to both plants and humans. Cultivation of maize (Zea mays L.), one of the most important crops worldwide, has been severely affected by B toxicity, thereby threatening human and animal food security. The effects of coating maize seed with B, zinc (Zn), and B+Zn were evaluated using transcriptome analysis. It was found that Zn coating significantly reduce B accumulation and toxicity in maize. Compared to the uncoated control, expression of 10871, 2844, and 1347 genes demonstrated alterations in response to coating with B, Zn, and B+Zn, respectively. Of the differentially expressed genes (DEGs), the expression of 7529, 1056, and 357 DEGs was found to be specific for coating with B, Zn, and B+Zn, respectively. Additionally, 132 co-modulated DEGs were found to primarily encode stress resistance- and membrane-related proteins. These genes were primarily involved in plant hormone signal transduction, ribosome assembly, carbon metabolism, phenylpropanoid biosynthesis, and oxidative phosphorylation pathways. Overall, our results suggested that seed coating with Zn significantly alleviates B accumulation and toxicity in maize by changing the expression of selected genes and constitutes a simple and effective strategy for alleviating B toxicity in high-B soils.

Toxicity of boron and vanadium nanoparticles on Danio rerio embryos - Phenotypical, biochemical, and behavioral alterations.

Engineered nanoparticles (NPs) are emerging contaminants of concern and it is important to understand their environmental behavior and ecological risks to exposed organisms. Despite their ubiquitous presence in the environment, there is little information about the hazards of certain NPs, such as boron (BNPs) and vanadium (VNPs). The aim of the present research was to investigate the effects of commercial BNPs and VNPs (80 to 100 nm) to zebrafish embryos, at different levels of biological organization. A range of nominal concentrations for both NPs (0, 0.01, 0.1, 1, and 10mg/L) was tested. Due to the presence of triton X-100 in the NPs' stock dispersions, an additional control group was included (0.001% triton X-100). Survival, hatching, and malformations of embryos were assessed for 96 hours (h) exposure. Locomotor behavior was evaluated at 120 h. Furthermore, embryos were exposed to 0, 1, and 10 mg/L of NPs to evaluate a set of biomarker responses after 96 h: cholinesterase (ChE) and glutathione S-transferase (GST) activities, total glutathione (TG) and energy budgets levels. VNPs induced malformations (10 mg/L), hyperactivity (10 mg/L), erratic swimming (0.01 mg/L), altered swimming pattern (>0.01 mg/L), delayed hatching (10 mg/L) and altered biochemical responses involved in antioxidant defense (GST and TG at >1 mg/L), neurotransmission (ChE at 10 mg/L) and energy metabolism (lipids at >1 mg/L and carbohydrates at 10 mg/L). BNPs caused malformations (10 mg/L), affected swimming pattern (>0.01 mg/L), induced erratic swimming (10 mg/L) and decreased TG content and GST activity (>1 mg/L). At the same concentrations, VNPs affected a greater number of endpoints than BNPs, demonstrating a greater toxicity to zebrafish embryos. The present study shows that BNPs and VNPs may affect aquatic organisms, albeit at relatively great non-environmentally relevant concentrations, reinforcing the importance of the risk assessment of different NPs.

Morphological responses and tolerance of a tree native to the Brazilian Cerrado Astronium fraxinifolium Schott to boron toxicity

The indiscriminate use of fertilizers and chemical pesticides can lead to boron contamination of the soil. Decontamination in general is expensive and results in other impacts. Phytoremediation is a sustainable alternative for soil restoration. Astronium fraxinifolium Schott (Anacardiaceae) is a tree species native to the Cerrado that is considered to be a pioneer species and a selective xerophyte, and it has been widely used in the reforestation and restoration of degraded areas. This study set out to characterize the physiology and anatomy of A. fraxinifolium under different boron concentrations and to assess the tolerance and phytoremediation potential of the species. An experiment with a completely randomized design was conducted in a greenhouse. The carbon allocation and chlorophyll content of leaves of A. fraxinifolium were determined. Boron concentration and the species' tolerance index were calculated from root and shoot samples. Levels of amino acids, proteins, total carbohydrates, starch, phenolic compounds, and anatomical analysis were also measured. A. fraxinifolium showed tolerance to boron concentrations in the substrate and accumulated a greater amount of the element in the aerial part, showing its phytoextraction ability. No significant differences were found in the physiology of A. fraxinifolium; however, some anatomical changes were observed. In the leaves, there were changes in the thickness of the abaxial surface of the epidermis and palisade and spongy parenchyma, and total leaf thickness, and in the roots, there were changes in the thickness of the phloem, diameter of vessel elements, and number of vessel elements per square millimeter. However, boron did not interfere in the development and survival of A. fraxinifolium, which points to the possibility that the species has phytoremediation potential.

Response to Application and Tissue Diagnosis of Boron Deficiency and Toxicity in Maize

ABSTRACT The experiments were conducted to verify the effect of doses and application time of boron (B) in the grain yield of maize and to study different plant tissues as a nutritional diagnosis tool for B. Six doses of B (0, 1, 2, 3, 4 and 12 kg ha−1) and two application times (before at sowing and V6 growth stage) were tested. In the first growing season, the B doses and application time did not influence yield components of maize. While the second growing season, B application reached maximum grain yield with 5.0 kg ha−1 at sowing, but at a high dose provided toxicity causing injuries in the cobs. In general, the B content in the leaf at flowering stage was higher with the application at V6 growth stage. B content and distribution in the leaves close to the cob vary with the rainfall that occurs before to the collection, harming the definition of the critical leaf level. The B content in the silk can be a reliable alternative for checking the deficiency or toxicity of this nutrient in the plant, presenting critical level for deficiency (calculated) of 23.2 mg kg−1 while values above 31.5 mg kg−1 can be considered toxic.

Safety of calcium fructoborate as a novel food pursuant to Regulation (EU) 2015/2283.

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on calcium fructoborate as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The NF, produced by chemical synthesis, contains a maximum of 2.9% of boron and on average 4.7% calcium and 84.2% fructose. It is intended to be marketed as food supplements targeting the general adult population, excluding pregnant and lactating women, at a maximum level of 220 mg/day (maximum boron intake of 6.4 mg per day). The combined intake of boron from the background diet and the NF is in the range of 9.6–9.9 mg/day (corresponding to up to 0.14 mg/kg body weight (bw) per day given a default bw of 70 kg). This is in the range of the acceptable daily intake (ADI) of 0.16 mg/kg bw per day. Under conditions mimicking the gastrointestinal (GI) environment, the NF is fully hydrolysed and the Panel considered boron toxicity relevant for the safety assessment. The Panel considers that there is no concern with respect to genotoxicity of the NF. The effect induced by the NF in a 13‐week rat study is consistent with toxicological findings induced by treatment with boron compounds in animal studies. Epididymides‐to‐brain weight ratio was identified as the most relevant endpoint and the reference point derived was the lowest model averaged BMDL10 value of 529 mg/kg bw per day. This corresponds to 14.8 mg/kg bw per day of boron, which is higher than the critical no observed adverse effect level (NOAEL) (9.6 mg boron/kg bw per day) used for establishing the ADI of 0.16 mg/kg bw per day for boron. The Panel therefore applied the present ADI for boron in the assessment of the NF. The Panel concludes that the NF, calcium fructoborate, is safe under the proposed uses and use levels.

CHITOSAN AGAINST TO BORON TOXICITY IN MAIZE

In this study; growth, chlorophyll, carotenoid, proline and MDA contents, the amounts of reactive oxygen species (ROS) (superoxide (O2.-) and hydrogen peroxide (H2O2)), and antioxidants (superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR) activities and its isoenzyme profiles, (ascorbate (AsA), dehydro ascorbate (DHA) and glutathione (GSH)) quantities in maize plants ((Zea mays L. cv. Hido) exposed to boron toxicity (B) (8 mM B(OH)3) and B+chitosan (0.01%, foliar (A) and seed soaking (B) applications) conditions in hydroponic culture have been studied comparatively. Boron toxicity significantly reduced growth parameters, chlorophyll, carotenoid, AsA, DHA and CAT activity while increased proline, MDA, oxidants (O2.- and H2O2), SOD, POD, APX and GR activities and GSH levels. B+Chitosan A and B applications significantly reversed the B toxicity-based inhibition in these parameters. It has been suggested that chitosan can be used as a reliable chemical for boron toxicity in maize, since chitosan applications (A and B) cause improvements in terms of all the parameters in the damage caused by B toxicty.

Genome-wide identification of Brassicaceae B-BOX genes and molecular characterization of their transcriptional responses to various nutrient stresses in allotetraploid rapeseed

BackgroundB-box (BBX) genes play important roles in plant growth regulation and responses to abiotic stresses. The plant growth and yield production of allotetraploid rapeseed is usually hindered by diverse nutrient stresses. However, no systematic analysis of Brassicaceae BBXs and the roles of BBXs in the regulation of nutrient stress responses have not been identified and characterized previously.ResultsIn this study, a total of 536 BBXs were identified from nine brassicaceae species, including 32 AtBBXs, 66 BnaBBXs, 41 BoBBXs, 43 BrBBXs, 26 CrBBXs, 81 CsBBXs, 52 BnBBXs, 93 BjBBXs, and 102 BcBBXs. Syntenic analysis showed that great differences in the gene number of Brassicaceae BBXs might be caused by genome duplication. The BBXs were respectively divided into five subclasses according to their phylogenetic relationships and conserved domains, indicating their diversified functions. Promoter cis-element analysis showed that BBXs probably participated in diverse stress responses. Protein-protein interactions between BnaBBXs indicated their functions in flower induction. The expression profiles of BnaBBXs were investigated in rapeseed plants under boron deficiency, boron toxicity, nitrate limitation, phosphate shortage, potassium starvation, ammonium excess, cadmium toxicity, and salt stress conditions using RNA-seq data. The results showed that different BnaBBXs showed differential transcriptional responses to nutrient stresses, and some of them were simultaneously responsive to diverse nutrient stresses.ConclusionsTaken together, the findings investigated in this study provided rich resources for studying Brassicaceae BBX gene family and enriched potential clues in the genetic improvement of crop stress resistance.

Quantifying the boron demand of Pelargonium graveolens for optimum biomass yield and quality of essential oil under field conditions

Deficiency and toxicity of micronutrient boron (B) play a critical role in plant productivity. In this study, the evaluation of B supplementation on biomass and essential oil (EO) yield of rose-scented geranium (Pelargonium graveolens L.) and its distribution at different application rates (2.5, 5.0, and 7.5 kg ha−1) was performed in a field trial during the growing season of two consecutive years 2017–18 and 2018–19. Boron uptake, plant biomass, and EO yield along with EO constituent in leaves were determined at different time scales. Application of B significantly improved the biomass yield of P. graveolens and at B-II treatment (5.0 kg ha−1 dose) highest biomass and EO yield was recorded, however, B-III treatment (7.5 kg ha−1) demonstrated toxicity symptoms like the decline in protein and chlorophyll content and an increase in proline and stress enzymes (SOD, CAT) in plant leaves. The effects of B on EO constituents varied with the different developmental stages of P. graveolens. Furthermore, the application of B at 5.0 kg ha−1 acts as a stimulant in upgrading the quality and quantity of EO with improved main aroma constituent’s P. graveolens than the control without modulating odor quality i.e., citronellol:geraniol (C:G) ratio. Hence, the study revealed a balanced level of B as a crucial parameter for the enhanced productivity with the improved economic return of P. graveolens.

The Effect of Boron Stress on Germination Properties of Pepper, Eggplant and Watermelon Seeds Subjected to Salicylic Acid Pre-application

Boron toxicity constitutes a limiting factor on seed germination. Salicylic acid-like plant growth regulators play an important role in alleviation the negative effects of boron stress. The research was carried out to determine the germination properties of seeds (pepper, eggplant, watermelon) with and without salicylic acid (SA) pre-application at different boron (B) concentrations. Experiments were conducted in randomized plots design with 4 replications. Seed germination percentage, mean germination time, germination index and germination energy values were determined under four different SA (0, 0.5, 1.0 and 2.0 mM) and six different B (0, 1.0, 2.0, 4.0, 8.0 and 16.0 mg L-1) doses. The greatest germination percentage, index and energy values and the shortest mean germination time were obtained from 1.0 mg L-1 B dose, on the other hand, increasing B stress negatively influenced germination parameters. Especially at 4.0, 8.0 and 16.0 mg L-1 B stress, 1.0 mM SA supplemented into growing media increased germination parameters of all three vegetable species, reduced the negative effects of boron and positively influenced germination time. Present findings revealed that SA could be used as an efficient tool in alleviation of negative effects of boron toxicity. On the other hand, SA applications were not effective or had quite limited effects on non-B application or low B-application (< 1.0 mg L-1) seeds

Repression of transcription factor AtWRKY47 confers tolerance to boron toxicity in Arabidopsis thaliana

Boron (B) excess gives rise to a serious agricultural problem. In this study, we identified a B toxicity responsive transcription factor AtWRKY47 in Arabidopsis thaliana. The T-DNA insertion mutants Atwrky47 showed enhanced tolerance to B toxicity with better growth parameters under high B conditions compared to wild-type Col-0 plants. Quantitative analysis of AtWRKY47 mRNA abundance indicated that it was down-regulated under B toxicity conditions. Fluorescently labeled AtWRKY47 protein was localized in nucleus. In contrast to the phenotype of Atwrky47 mutants, overexpression of AtWRKY47 in Col-0 background resulted in lower biomass, less chlorophyll content, and increased sensitivity to B toxicity. More importantly, the B concentration in shoots was higher in the overexpression lines and lower in the Atwrky47 mutants than in Col-0 plants, respectively. These results demonstrate that AtWRKY47 gene plays a key role in regulating plant tolerance to B toxicity.

Determination of Morphological and Physiological Changes of Ornamental Cabbage (Brassica oleracea var. acephala) against Boron Toxicity in Phytoremediation

Boron toxicity in agricultural lands limits plant breeding as a plant nutrition problem. Some plants are able to tolerate high levels of heavy metals at potentially toxic doses, accumulate them in their bodies and remove them from the soil. In this study, it was aimed to determine the morphological and physiological responses of ornamental cabbage in phytoremediation against boron toxicity. This study was conducted under controlled greenhouse conditions, 4 different boron doses (0, 10, 25, and 50 mg kg-1 B) were applied to 2 different soil structures (acidic (S1) and alkaline (S2) soils). Toxicity symptoms were appeared at 50 mg kg-1 B. At alkaline soil, plant weights and visual properties of plants were found to be low in quality. Results show that as the boron dose increased, shoot-root fresh and dry weight, stomatal conductance, chlorophyll content, relative water content (RWC) were decreased. Boron accumulation in the shoot, root and whole plant was at 50 mg kg-1 B. As a result, it is understood that ornamental cabbage used for decontamination of boron element by phytoremediation method for the first time in this study. We suggest that it has a potential to as hyper-accumulator plant for the remediation of boron-contaminated soil.

The involvement of the induction of anthocyanin biosynthesis and transport in toxic boron responsive regulation in Arabidopsis thaliana

Recently, boron (B) has been found to form a complex with anthocyanin, which could be evidence for the B tolerance mechanisms that reduce free B in the leaf tissues of plants. However, the molecular mechanism of anthocyanin biosynthesis and transport has not been satisfactorily elucidated in plants exposed to toxic B. Therefore, the changes in expression levels of some of the phenylpropanoid pathway genes, early and late flavonoid biosynthetic genes, and transcription factors related to anthocyanin biosynthesis and transport were determined in Arabidopsis thaliana under B toxicity. Accordingly, 1 mM boric acid treatment did not cause any significant change in the expression levels of anthocyanin biosynthesis genes such as PAL1, PAL2, C4H, 4CL3, CHS, ANS and transcription factors such as MYBD and TT8 in Arabidopsis thaliana. However, 3 mM boric acid treatment induced the expression levels of anthocyanin biosynthesis genes such as C4H, 4CL3 and transcription factors including MYB75, MYB114 and anthocyanin transporter genes such as TT13 and TT19. In addition to B-anthocyanin, B-anthocyanins conjugated with glutathione (GSH) complexes can also participate in the internal B tolerance mechanism in plants. Therefore, the direct role of the B-anthocyanin complex without GSH conjugation needs to be determined. For this purpose, anthocyanin accumulation was determined in slim1 mutant Arabidopsis thaliana exposed to excess B because SLIM1 transcription factor activates sulfate acquisition for S assimilation, which generates cysteine, the substrate for GSH. Accordingly, it was gradually increased through increasing toxic B levels in both wild type (WT) and slim1 mutant plants. slim1 mutant had more anthocyanin accumulation than WT under control and all toxic B conditions. In conclusion, increases in expression levels of MYB75, MYB114, TT13, TT19 and in anthocyanin level in slim1 mutant in response to increased toxic B levels showed that anthocyanins may play a primary role in B tolerance in plants.

Thin-film nanocomposite membrane comprised of a novel phosphonic acid derivative of titanium dioxide for efficient boron removal

The separation of toxic boron from seawater is the main concern for the desalination industries. The membrane-based boron separation is challenging due to the existence of boron in the neutral boric acid form. According to World Health Organization, a Boron above 0.5 ppm is not recommended for human health and agricultural use. The design of NF membranes for the Boron separation is tricky due to its neutral charge. In this study, a novel modification of titanium dioxide (TiO2) nanoparticles is performed by reacting with the cyclic propyl phosphonic anhydride (T3P) reagent in the presence of triethylamine as a base to obtain the phosphonic acid derivative of TiO2 (PTiO2). The PTiO2 was used as inorganic filler during the coating of the polyamide layer on the ultrafiltration support. Better dispersion of the nanoparticles was achieved due to the effective interactions between the –POOH (of PTiO2) and –NH2 (of meta-phenylene diamine groups) as evidenced by the ATR-IR spectrum. The resultant nanocomposite membranes showed a high potential to reject scalant divalent ions (>98%) and sodium chloride (>60%) with improved permeation characteristics. The boron adsorption study revealed a strong adsorption of boric acid ~12 mg/g by the PTiO2 nanoparticles causing the pore narrowing effect. Due to the same reason, the boron diffusion coefficient of the membranes reduced at neutral pH. The boron rejection offered by the membrane with 0.1 wt% PTiO2 was ~2.5 times higher than the commercial NF90 membrane.

Impact of boric acid and saline water irrigation on germination and seedling establishment of wheat*

AbstractThe main purpose of this experiment was to investigate the effects of salinized water with boric acid and sodium chloride (NaCl) on seed germination and seedling establishment of wheat. The following treatments were applied: Boric acid solution (0, 40, 240, and 480 μM) and NaCl solution (0, 50, 250, and 1,000 μM) were combined to produce 16 different solutions. The highest germination percentages were found in distilled water. Shoot length and root length of wheat were reduced by increments of all boric acid treatments in both saline solution and distilled water, but the decrease in shoot length due to boron toxicity was significant more pronounced in saline conditions. The greatest shoot and root lengths were observed in the control treatment (distilled water), and the smallest lengths were observed in the highest boric acid treatment (480 μM). Shoot and root dry weight also decreased with increasing boric acid. The averages of variables were also significantly affected by salinity solutions, but to a greater extent than under the influence of boric acid. It is concluded that wheat plants cannot tolerate salinized water with boric acid and NaCl during the germination stage.

A Comparative Study on the Effect of Acute Toxicity of Nano and Micro Boron Particles in Lemna minor (Linneaus 1753)

In recent years, studies have shown that uncertainties such as nanoparticle effects on plants, knowledge gaps and toxicity mechanisms have been significantly displayed. In this study physiological effects and the main factors contributing to nano and micro Boron (B) toxicity in duckweed (Lemna minor) under experimental conditions were investigated. This study reports that that chlorophyll contents of treated nano B are higher than the control group and the treated micro B. Malondialdehyde and superoxide dismutase levels were recorded higher in micro B. Catalase and hydrogen peroxide level were recorded higher in nano B. Pearson's correlation analysis showed negative correlations between hydrogen peroxide and malondialdehyde levels in all doses of nano B; Positive correlations were found between malondialdehyde and catalase levels at 100 mg /L of micro B. The accumulation in leaf tissues of the duckweed decreased by the increase in the concentration of nano B. On the contrary, micro B, as the concentration of micro B increases the accumulation of plant tissue.

Cross species multi-omics reveals cell wall sequestration and elevated global transcript abundance as mechanisms of boron tolerance in plants.

Boron toxicity is a world-wide problem for crops, yet we have a limited understanding of the genetic responses and adaptive mechanisms to this stress in plants. We employed a cross-species comparison between boron stress-sensitive Arabidopsis thaliana and its boron stress-tolerant extremophyte relative Schrenkiella parvula, and a multi-omics approach integrating genomics, transcriptomics, metabolomics and ionomics to assess plant responses and adaptations to boron stress. Schrenkiella parvula maintains lower concentrations of total boron and free boric acid than Arabidopsis when grown with excess boron. Schrenkiella parvula excludes excess boron more efficiently than Arabidopsis, which we propose is partly driven by SpBOR5, a boron transporter that we functionally characterize in this study. Both species use cell walls as a partial sink for excess boron. When accumulated in the cytoplasm, excess boron appears to interrupt RNA metabolism. The extremophyte S. parvula facilitates critical cellular processes while maintaining the pool of ribose-containing compounds that can bind with boric acid. The S.parvula transcriptome is pre-adapted to boron toxicity. It exhibits substantial overlaps with the Arabidopsis boron-stress responsive transcriptome. Cell wall sequestration and increases in global transcript levels under excess boron conditions emerge as key mechanisms for sustaining plant growth under boron toxicity.

Salicylic acid-mediated alleviation of soil boron toxicity in Mentha arvensis and Cymbopogon flexuosus: Growth, antioxidant responses, essential oil contents and components

Boron (B) toxicity is a notable abiotic hindrance that restricts crop productivity by disturbing several physiological and biochemical processes in plants. This study was aimed to elucidate the role of salicylic acid (SA) in conferring tolerance to B stress in Mentha arvensis and Cymbopogon flexuosus. Boron toxicity led to a considerable decrease in shoot height and root length, fresh and dry mass of shoot and root, and physiological and biochemical parameters. However, exogenously applied SA relieved the adverse effects caused by B toxicity and led to an increase in growth parameters under B stress and non-stress conditions. The treatment of B resulted in its increased accumulation in roots and shoots of both the plants which, in turn, caused oxidative damage as evident by increased content of malondialdehyde and catalase, peroxidase, superoxide dismutase and glutathione reductase enzyme activities. However, exogenous SA supply significantly affected antioxidant enzyme activities and protected the plants from excess B. Moreover, the essential oil content of two selected plants declined under B toxicity and significantly enhanced in SA-treated stressed plants. The contents of menthol and menthyl acetate in M. arvensis were lowered in B stressed plants which significantly improved in SA treated B-stressed and in their respective SA alone treatment. Similarly, citral-A and citral-B content of C. flexuosus declined under B toxicity, however, SA reversed the negative effects of B toxicity on essential oil components. This assessment stipulated the promising role of exogenously applied SA in alleviating B toxicity in M. arvensis and C. flexuosus by improving antioxidant machinery and limiting B uptake which protects the structural integrity of leaves and also helps in increasing essential oil content.

Reproductive development and pollen-stigma interaction in sunflower plants receiving boron deficient and toxic supply

To study the effect of boron deficiency and toxicity on the reproductive development and pollen-stigma interaction in sunflower (Helianthus annuus var. Sungold), plants were raised in sand culture under glass house condition till maturity at 0.033 (deficient), 0.33 (sufficient) and 3.3 (toxic) mg B L−1 supply. The effect of deficiency and toxicity of boron on the number, size and weight of inflorescence, anther size, pollen producing capacity (PPC) of an anther and pollen viability were determined. Enzymes peroxidase, acid phosphatase and esterase and protein were cytochemically localized on the stigmatic surface of disk floret. As compared to control plants (0.33 mg B L−1 supply) development of inflorescence was not only delayed but also poor under boron deficiency and toxicity. Pollen grains produced under boron deficiency and toxicity had reduced size with low viability. Histochemical localization of proteins showed marked decrease in concentration on the stigmatic surface of plants receiving deficient and toxic boron supply. Cytochemical localization of peroxidase enzymes on the stigmatic surface showed increased activity whereas a decrease in acid phosphatase and esterase activity was observed suggesting poor pollen stigma interaction under boron stress condition which might be the cause of poor fertilization.