Boron application mitigates Cd toxicity in leaves of rice by subcellular distribution, cell wall adsorption and antioxidant system

Boron contributes to enhance antimony tolerance in rice (Oryza sativa L.) by activating antioxidant system, modifying the cell wall component and promoting cell wall deposition of Sb

Boron (B) is essential for plant growth and helps mitigate metal toxicity in various crop plants. However, the potential role and underlying mechanisms of B in alleviating antimony (Sb) toxicity in rice remain unexplored. In this study, we investigated the effects of H₃BO₃ supplementation (30, 50, and 75 μM) on morphological growth, physiological and biochemical traits, Sb content, and the subcellular distribution of Sb in rice plants under 100 μM Sb stress during the seedling stage in a hydroponic system. The results revealed that Sb toxicity severely impaired rice growth, reducing shoot biomass by 38.3%, shoot and root length by 38.9% and 23.2%, and leaf relative water content by 15.5%. Supplementation with 30 μM B mitigated these adverse effects by enhancing photosynthesis and chlorophyll synthesis, restoring root activity, and improving oxidative balance through increased antioxidant enzyme activities in rice tissues. Furthermore, B supplementation significantly reduced Sb concentration in roots by 56.28%, while promoting Sb distribution in the cell wall (CW) fraction. Scanning electron microscopy equipped with energy-dispersive X-ray (SEM-EDS) microanalysis confirmed that B enhanced Sb adsorption on root CWs. Fourier transform infrared spectroscopy (FTIR) analysis indicated increased carboxyl groups in the CWs following B application under Sb treatment. Moreover, B supplementation increased the levels of pectin and hemicellulose and elevated pectin methylesterase (PME) activity by 22.0%, 69.0%, and 29.0% in roots, respectively, thus promoting Sb chelation onto the CWs. Taken together, our results provide a scientific basis and theoretical guidance for applying B to alleviate Sb toxicity in crops.

Mechanism of foliar application of boron to alleviate cadmium toxicity in winter wheat (Triticum aestivum L.)

Our previous work shown that boron (B) can inhibit cadmium (Cd) absorption in winter wheat, while the mechanism is not well understood. In this study, the mechanism of foliage spray B on Cd uptake in Cd-contaminated farmland was characterized with three treatments: spraying distilled water (CK), spraying 0.3% B fertilizer (F0.3%), and spraying 0.6% B fertilizer (F0.6%). The spraying treatment was conducted during the jointing stage and booting stage, respectively. The objective was to investigate the impact of different concentrations of B fertilizer application on Cd content, yield, physiological biochemical response, Cd transporter in wheat. Results showed that the yield increased with increasing B spray concentration compared with CK treatment. The wheat yield increased by 1.29%∼12.50% under foliar B application. The Cd concentration in both shoot and root of wheat seedlings were significantly decreased with foliar application of B at jointing stage and booting stage. The Cd concentrations in root and seed were also decreased with B treatment at maturity stage, especially after treatment with F0.6%, the Cd absorption in wheat grains exhibited a significant reduction of 31.20%. In addition, foliar application of B significantly increased antioxidant enzyme activities, include APX, SOD, CAT, and POD. Compared with CK, the MDA content in leaves showed a significant decrease with 30.48%-50.14%, while the GSH content showed an increase with 76.32%-1.05%. The down-regulation of the uptake and transport genes (TaNramp5, TaLCT1 and TaHMA2) and the up-regulation of compartmentalization transport genes (TaTM20 and TaHMA3) may contribute to the reduction of Cd accumulation in shoot. Overall, our results suggest that foliar spraying of B could increase B accumulation and yield, and alleviate Cd toxicity by reducing Cd uptake, enhancing the antioxidant capacity, regulating the expression of Cd genes in wheat.

Synergistic effects of boron and cadmium on the metal enrichment and cell wall immobilization capacity of Cosmosbipinnatus

Cadmium (Cd), as a heavy metal pollutant, can seriously affect plant growth and development. Boron (B), as an indispensable nutrient element, plays an important role in plant growth and cell wall (CW) synthesis. However, the physiological effects of B and Cd on plant growth and the mechanism of Cd chelation by the CW remain unclear. Here, we investigate the effect of exogenous B on Cd accumulation in CW components of Cosmos bipinnatus roots and its mechanism of Cd mitigation. Under B deficiency and single Cd (30 μM) treatments, the growth of C. bipinnatus was significantly inhibited, but the addition of exogenous B significantly increased plant biomass, which increased the Cd content in the underground parts of C. bipinnatus by 20.18% and reduced the Cd translocation factor by 22.22%. Meanwhile, application of exogenous B affected the subcellular Cd content across various Cd forms and alleviated Cd-induced oxidative stress in C. bipinnatus. Additionally, exogenous B and Cd and their mixtures affected the functional groups of the root CW, the proportion of polysaccharide components, the Cd content of polysaccharides, and the polysaccharide uronic acid content of C. bipinnatus. However, B application increased 3-deoxy-oct-2-ulosonic acid content, pectin esterase activity, low esterified pectin content, and its Cd content by 149.52%, 55.69%, 206.38%, and 150.02%, respectively, compared to Cd treatment alone. Thus, our study showed that B mitigates the toxicity of Cd to plants, revealing the effect of B on the physiological aspects of Cd tolerance in plants.

Variation in phytotoxicity of rice seedlings caused by differential accumulation of azoxystrobin and pyraclostrobin in leaves

The effectiveness of pyraclostrobin (Pyr) and azoxystrobin (Azo) with highly targeting the rice blast is noteworthy, but they have varied toxic levels towards non-target aquatic organisms. Nevertheless, the toxic selectivity and mechanism of non-target plants, specifically rice, remain uncertain. In this study, we investigated the potential phytotoxic effects of Pyr and Azo on rice seedlings, including plant morphology, plant growth, physiological and biochemical changes. The findings revealed that both Pyr and Azo caused toxic effects on rice, resulting in symptoms of chlorosis and inhibited growth. The toxicity of Azo was found to be more severe when applied at the recommended field dose. Disruption of oxidative stress could significantly impact the demonstrated levels of REC, leading to a decrease in photosynthetic pigments and potentially culminating in cell death. Furthermore, the toxic effect of Azo had a greater impact on rice leaves compared to Pyr at treatments of 400, 800, 1600, and 4000 mg/L. However, the in vitro cytotoxicity of Azo on rice leaves was lower than that of Pyr. Therefore, it can be inferred that the mechanism of phytotoxicity of Azo is directly linked to the increased accumulation of the compound on the leaf tips and edges. Additionally, the positive effects observed on plant morphology and growth parameters suggest that the mixed application of plant growth regulators (sodium nitrophenolate aqueous solution of 14 mg/L and diethyl aminoethyl hexanoat of 50 mg/L) can be a promising approach to mitigate the rice phytotoxicity of Azo at 400 and 800 mg/L.

Impact of Abiotic Stress on Rice and the Role of DNA Methylation in Stress Response Mechanisms

With the intensification of global climate change and the increasing complexity of agricultural environments, the improvement of rice stress tolerance is an important focus of current breeding research. This review summarizes the current knowledge on the impact of various abiotic stresses on rice and the associated epigenetic responses (DNA methylation). Abiotic stress factors, including high temperature, drought, cold, heavy metal pollution, and high salinity, have a negative impact on crop productivity. Epigenetic changes are key regulatory factors in plant stress responses, and DNA methylation is one of the earliest discovered and thoroughly studied mechanisms in these epigenetic regulatory mechanisms. The normal growth of rice is highly dependent on the environment, and changes in the environment can lead to rice sterility and severe yield loss. Changes in the regulation of the DNA methylation pathway are involved in rice's response to stress. Various DNA methylation-regulating protein complexes that function during rice development have been identified. Significant changes in DNA methylation occur in numerous stress-responsive genes, particularly those in the abscisic acid signaling pathway. These findings underscore the complex mechanisms of the abiotic stress response in rice. We propose the effective improvement of tolerance traits by regulating the epigenetic status of rice and emphasize the role of DNA methylation in abiotic stress tolerance, thereby addressing global climate change and ensuring food security.

Role of boron and its interaction with other elements in plants

Boron (B) is an essential microelement for plants, and its deficiency can lead to impaired development and function. Around 50% of arable land in the world is acidic, and low pH in the soil solution decreases availability of several essential mineral elements, including B, magnesium (Mg), calcium (Ca), and potassium (K). Plants take up soil B in the form of boric acid (H3BO3) in acidic soil or tetrahydroxy borate [B(OH)4]- at neutral or alkaline pH. Boron can participate directly or indirectly in plant metabolism, including in the synthesis of the cell wall and plasma membrane, in carbohydrate and protein metabolism, and in the formation of ribonucleic acid (RNA). In addition, B interacts with other nutrients such as Ca, nitrogen (N), phosphorus (P), K, and zinc (Zn). In this review, we discuss the mechanisms of B uptake, absorption, and accumulation and its interactions with other elements, and how it contributes to the adaptation of plants to different environmental conditions. We also discuss potential B-mediated networks at the physiological and molecular levels involved in plant growth and development.

Transcriptome and ultrastructural analysis revealed the mechanism of Mercapto-palygorskite on reducing Cd content in wheat

Large areas of crop yields in northern China have faced with cadmium (Cd) contamination problems. Mercapto-modified palygorskite (MP), as a highly efficient immobilization material, could reduce Cd absorption in wheat and alleviate its biotoxicity. However, the molecular mechanism underlying MP-mediated Cd reduction and detoxification processes in wheat is not well understood. This aim of this study was to investigate the biochemical and molecular mechanisms underlying the reduction in Cd accumulation in wheat (Triticum aestivum L.). The results showed that MP application decreased the Cd concentration by 68.91-74.32% (root) and 70.68-77.2% (shoot), and significantly increased the glutathione (GSH) and phytochelatins (PCs) contents in root and shoot. In addition, with the application of MP, the percentage of Cd in the cell walls and organelles of wheat decreased, while that of Cd in soluble components was increased. The content of Cd in all components was significantly reduced. Ultrastructural analysis revealed that MP thickened the cell wall, promoted vesicle formation in the membrane and protected the integrity of intracellular organelles in wheat. Transcriptome analysis further confirmed the above results. MP upregulated the expression of several genes (CCR, CAD COMT and SUS) involved in cell wall component biosynthesis and promoted vesicle formation on cell membranes by upregulating the expression of PLC and IPMK genes. In addition, genes related to antioxidant synthesis (PGD, glnA and GSS) and photosynthesis (Lhca, Lhcb) were altered by MP to alleviate Cd toxicity in wheat. This present work will help to more thoroughly elucidate the molecular mechanism by which wheat defends against Cd contamination under MP application and provide and important research basis for the application of this material in the future.

Inoculation of cadmium-tolerant bacteria to regulate microbial activity and key bacterial population in cadmium-contaminated soils during bioremediation

The perennial ryegrass Lolium perenne can be used in conjunction with cadmium (Cd)-tolerant bacteria such as Cdq4-2 (Enterococcus spp.) for bioremediation of Cd-contaminated soil. In this study, a theoretical basis was provided to increase the efficiency of L. perenne remediation of Cd-contaminated soil using microorganisms to maintain the stability of the soil microbiome. The experimental design involved three treatment groups: CK (soil without Cd addition) as the control, 20 mg·kg-1 Cd-contaminated soil, and 20 mg·kg-1 Cd-contaminated soil + Cdq4-2, all planted with L. perenne. The soil was collected on day 60 to determine the soil microbial activity and bacterial community structure and to analyze the correlation between soil variables, the bacterial community, available Cd content in the soil, Cd accumulation, and L. perenne growth. The soil microbial activity and bacterial community diversity decreased under Cd stress, and the soil microbial community composition was changed; while inoculation with Cdq4-2 significantly increased soil basal respiration and the activities of urease, invertase, and fluorescein diacetate (FDA) hydrolase by 83.65%, 79.72%, 19.88%, and 96.15% respectively; and the stability of the community structure was also enhanced. The Actinobacteriota biomass, the amount of available Cd, and the above- and belowground Cd content of L. perenne were significantly negatively correlated with the total phosphorus, total potassium, and pH. The activity of urease, invertase, and FDA hydrolase were significantly positively correlated with the biomasses of Acidobacteriota and L. perenne and significantly negatively correlated with the Chloroflexi biomass. Further, the available soil Cd content and the above- and belowground Cd levels of L. perenne were significantly positively correlated with the Actinobacteriota biomass and significantly negatively correlated with the Gemmatimonadetes biomass. Overall, inoculating Cd-tolerant bacteria improved the microbial activity, diversity, and abundance, and changed the microbial community composition, facilitating the remediation of Cd-contaminated soil by L. perenne.

Strontium alleviated the growth inhibition and toxicity caused by cadmium in rice seedlings

Cadmium (Cd) contamination of rice is an urgent ecological and agricultural problem. Strontium (Sr) has been shown to promote plant growth. However, the effect of Sr on rice seedlings under Cd stress is currently unclear. In this work hydroponic experiments were used to assess the impact of Sr on rice seedling growth under Cd stress. The findings demonstrated that foliar application of 0.5 mg L-1 Sr had no discernible impact on the development of rice seedlings. However, Sr significantly alleviated growth inhibition and toxicity in rice seedlings when threatened by Cd. Compared with the Cd treatment (Cd, 2.5 mg L-1), the root length, shoot height, and whole plant length of rice seedlings in the Cd + Sr treatment (Cd, 2.5 mg L-1; Sr, 0.5 mg L-1) increased by 4.96 %, 12.47 % and 9.60 %, respectively. The content of Cd in rice decreased by 23.34 % (roots) and 5.79 % (shoots). Sr lessened the degree of membrane lipid peroxidation damage (lower MDA concentration) among the seedlings of rice under Cd stress by controlling the activities of antioxidant enzymes and GSH content. By changing the expression of antioxidant enzyme-encoding genes and downregulating the heavy metal transporter gene (OsNramp5), Sr reduced accumulation and the detrimental effects of Cd on rice seedlings. Our study provides a new solution to the problem of Cd contamination in rice, which may promote the safe production of rice and benefit human health.

Inhibition Roles of Calcium in Cadmium Uptake and Translocation in Rice: A Review

Cadmium (Cd) contamination in rice grains is posing a significant threat to global food security. To restrict the transport of Cd in the soil-rice system, an efficient way is to use the ionomics strategy. Since calcium (Ca) and Cd have similar ionic radii, their uptake and translocation may be linked in multiple aspects in rice. However, the underlying antagonistic mechanisms are still not fully understood. Therefore, we first summarized the current knowledge on the physiological and molecular footprints of Cd translocation in plants and then explored the potential antagonistic points between Ca and Cd in rice, including exchange adsorption on roots, plant cell-wall composition, co-transporter gene expression, and transpiration inhibition. This review provides suggestions for Ca/Cd interaction studies on rice and introduces ionomics research as a means of better controlling the accumulation of Cd in plants.

A Dark Septate Endophyte Improves Cadmium Tolerance of Maize by Modifying Root Morphology and Promoting Cadmium Binding to the Cell Wall and Phosphate

Dark septate endophytes (DSEs) can improve the performance of host plants grown in heavy metal-polluted soils, but the mechanism is still unclear. A sand culture experiment was performed to investigate the effects of a DSE strain (Exophiala pisciphila) on maize growth, root morphology, and cadmium (Cd) uptake under Cd stress at different concentrations (0, 5, 10, and 20 mg·kg^-1). The results indicated that the DSE significantly improved the Cd tolerance of maize, causing increases in biomass, plant height, and root morphology (length, tips, branch, and crossing number); enhancing the Cd retention in roots with a decrease in the transfer coefficient of Cd in maize plants; and increasing the Cd proportion in the cell wall by 16.0-25.6%. In addition, DSE significantly changed the chemical forms of Cd in maize roots, resulting in decreases in the proportions of pectates and protein-integrated Cd by 15.6-32.4%, but an increase in the proportion of insoluble phosphate Cd by 33.3-83.3%. The correlation analysis revealed a significantly positive relationship between the root morphology and the proportions of insoluble phosphate Cd and Cd in the cell wall. Therefore, the DSE improved the Cd tolerance of plants both by modifying root morphology, and by promoting Cd binding to the cell walls and forming an insoluble phosphate Cd of lower activity. These results of this study provide comprehensive evidence for the mechanisms by which DSE colonization enhances Cd tolerance in maize in root morphology with Cd subcellular distribution and chemical forms.

Characterization of cadmium accumulation mechanism between eggplant (Solanum melongena L.) cultivars

Excessive cadmium (Cd) accumulation in vegetables due to farmland pollution constitutes a serious threat to human health. Eggplant has a tendency to accumulate Cd. To investigate the mechanism of the differences in Cd accumulation levels between high-Cd (BXGZ) and low-Cd (MYQZ) eggplant cultivar, physiological and biochemical indicators and mRNA expression of eggplant were examined using photosynthetic apparatus, biochemical test kits, Fourier transform infrared (FTIR) spectroscopy and transcriptome sequencing, etc. The results of biochemical test kits and FTIR revealed that MYQZ enhanced pectin methylesterase (PME) activity, and lignin and pectin content in the root cell wall, which was associated with the upregulation of PME, cinnamyl-alcohol dehydrogenase and peroxidase (PODs). Higher levels of cysteine and glutathione (GSH) contents and upregulation of genes associated with sulfur metabolism, as well as higher expression of ATP-binding cassette transporters (ABCs), cation exchangers (CAX) and metal tolerance proteins (MTPs) were observed in MYQZ. In BXGZ, the higher stomatal density and stomatal aperture as well as higher levels of Ca²⁺ binding protein-1 (PCaP1) and aquaporins and lower levels of A2-type cyclins (CYCA2-1) are consistent with an enhanced transpiration rate in BXGZ. Furthermore, a more developed root system was shown to be associated with higher levels of auxin response factor (ARF19), GATA transcription factors (GATA4, 5 and 11) and auxin efflux carrier component (PIN5) in BXGZ. In conclusion, highly active PME, and higher levels of lignin and pectin in MYQZ are expected to reduce Cd toxicity, while Cd translocation can be inhibited with the help of ABC and other Cd transporters. As for BXGZ, the uptake and translocation of Cd were enhanced by the developed root system and stronger transpiration.

Interaction between Boron and Other Elements in Plants

Boron (B) is an essential mineral nutrient for growth of plants, and B deficiency is now a worldwide problem that limits production of B deficiency-sensitive crops, such as rape and cotton. Agronomic practice has told that balanced B and other mineral nutrient fertilizer applications is helpful to promote crop yield. In recent years, much research has reported that applying B can also reduce the accumulation of toxic elements such as cadmium and aluminum in plants and alleviate their toxicity symptoms. Therefore, the relation between B and other elements has become an interesting issue for plant nutritionists. Here we summarize the research progress of the interaction between B and macronutrients such as nitrogen, phosphorus, calcium, potassium, magnesium, and sulfur, essential micronutrients such as iron, manganese, zinc, copper, and molybdenum, and beneficial elements such as sodium, selenium, and silicon. Moreover, the interaction between B and toxic elements such as cadmium and aluminum, which pose a serious threat to agriculture, is also discussed in this paper. Finally, the possible physiological mechanisms of the interaction between B and other elements in plants is reviewed. We propose that the cell wall is an important intermediary between interaction of B and other elements, and competitive inhibition of elements and related signal transduction pathways also play a role. Currently, research on the physiological role of B in plants mainly focuses on its involvement in the structure and function of cell walls, and our understanding of the details for interactions between B and other elements also tend to relate to the cell wall. However, we know little about the metabolic process of B inside cells, including its interactions with other elements. More research is needed to address the aforementioned research questions in future.

High boron stress leads to sugar beet (Beta vulgaris L.) toxicity by disrupting photosystem Ⅱ

This sugar beet acts as a soil remediator in areas where there are high levels of boron (B) in the soil, since it has a high requirement of boron (B) for growth, and has strong resistance to high B levels. Although B toxicity in different plants has been widely researched, little is known about the response of photosystem II (PSII) activity in sugar beet leaves to B toxicity at present. To clarify the growth and photosynthetic physiological response of sugar beet to B toxicity, the effects of different concentrations of H₃BO₃ (0.05, 1.5, 2.5,3.5 mM) on the growth, photosynthetic characteristics and antioxidant defense system of sugar beet seedlings were investigated by hydroponic experiments. In the present study, high B stress inhibited the growth of sugar beet and significantly decreased the biomass of the plants. There was a remarkable increase in the accumulation of B in the shoots, which affected photosynthesis and decreased the photosynthetic pigments. As B toxicity increased, leaf PSII activities and maximum photochemical efficiency of PSII (F_v/F_m) showed a tendency to decrease; at the same time, the photosynthetic performance index based on absorbed light energy (PI_ABS) decreased as well. Meanwhile, the energy allocation parameters of the PSII reaction center were changed, the light energy utilization capacity and the energy used for electron transfer were reduced and the thermal dissipation was increased at the same time. Furthermore, B toxicity decreased catalase (CAT) activity, increased peroxidase (POD) and superoxide dismutase (SOD) activities, and increased malondialdehyde (MDA) accumulation. According to the results obtained in this study, high B concentrations reduced the rate of photosynthesis and fluorescence, thus weakened antioxidant defense systems, and therefore inhibited the growth of sugar beet plants. Thus, in high B areas, sugar beet possesses excellent tolerance to high B levels and has a high B translocation capacity, so it can be used as a phytoremediation tool. This study provides a basis for the feasibility of sugar beet resistant to high B environments.

Dual RNA and 16S ribosomal DNA sequencing reveal arbuscular mycorrhizal fungi-mediated mitigation of selenate stress in Zea mays L. and reshaping of soil microbiota

Excessively high concentrations of selenium (Se) in soil are toxic to crop plants, and inoculation with arbuscular mycorrhizal fungi (AMF) can reverse Se stress in maize (Zea mays L.). To investigate the underlying mechanisms, maize seedlings were treated with sodium selenate (5 mg Se[VI] kg^-1) and/or AMF (Funneliformis mosseae and Claroideoglomus etunicatum). Dual RNA sequencing in mycorrhiza and 16 S ribosomal DNA sequencing in soil were performed. The results showed that Se(VI) application alone decreased plant dry weight, but increased plant Se concentration, total Se content (mainly selenocysteine), and root superoxide content. Inoculation with either F. mosseae or C. etunicatum increased plant dry weight, decreased Se accumulation and selenocysteine proportion, enhanced root peroxidase activity, and alleviated oxidative stress in Se(VI)-treated plants. Inoculation also downregulated the expression of genes encoding Se transporters, assimilation enzymes, and cysteine-rich receptor-like kinases in Se(VI)-stressed plants, similar to plant-pathogen interaction and glutathione metabolism related genes. Conversely, genes encoding selenium-binding proteins and those related to phenylpropanoid biosynthesis were upregulated in inoculated plants under Se(VI) stress. Compared with Se(VI)-free plants, Se tolerance index, symbiotic feedback percentage on plant dry weight, and root colonization rate were all increased in inoculated plants under Se(VI) stress, corresponding to upregulated expression of 'key genes' in symbiosis. AMF inoculation increased bacterial diversity, decreased the relative abundances of selenobacteria related to plant Se absorption (e.g., Proteobacteria and Firmicutes), and improved bacterial network complexity in Se(VI)-stressed soils. We suggest that stress-mediated enhancement of mycorrhizal symbiosis contributed to plant Se(VI) tolerance, whereas AMF-mediated reshaping of soil bacterial community structure prevented excessive Se accumulation in maize.

Lead exposure dose-dependently affects oxidative stress, AsA-GSH, photosynthesis, and mineral content in pakchoi (Brassica chinensis L.)

Lead (Pb) is a heavy metal pollutant and negatively affects agriculture and ecosystems. Pb can cause oxidative stress and abnormal plant growth. The ascorbic acid-glutathione (AsA-GSH) cycle mainly exists in chloroplasts and resists oxidative stress, scavenges reactive oxygen radicals, and maintains normal photosynthesis. However, the dosage related effects of Pb on pakchoi photosynthesis, via oxidative stress and the AsA-GSH system, remains unclear. In this study, various Pb dosage stress models were tested (low: 300 mg/kg; medium: 600 mg/kg; high: 900 mg/kg). Pb stress induced a dose-dependent increase in Pb content in pakchoi leaves (P < 0.05). Principal component analysis showed that Se, B, and Pb were significantly and negatively correlated. Pb stress also increased MDA content and decreased antioxidant enzymes SOD, GSH-Px, and T-AOC activities (P < 0.05). We also found that Vc content, as well as the GSH/GSSG ratio, decreased. Additionally, Pb stress destroyed chloroplast structure, decreased photosynthesis indicators Pn, Tr, Gs, Ci and VPD, and attenuated Fv/Fm and Fv/Fo (P < 0.05). In the high-dose group, the contents of chlorophyll a, chlorophyll b, and carotenoids decreased significantly, while the expression of chloroplast development genes (GLK, GLN2) decreased (P < 0.05). Our data suggest that Pb stress leads to dosage-dependent, aberrant photosynthesis by inhibiting the AsA-GSH system in pakchoi. This study expands the Pb toxicology research field and provides indications for screening antagonists.

Effect of boron on cadmium uptake and expression of Cd transport genes at different growth stages of wheat (Triticum aestivum L.)

Boron (B) is an essential microelement for plant growth and has been shown to reduce cadmium (Cd) toxicity in wheat through modulating gene expression. However, there is not enough information about the effects of different applications of B fertilizer on the accumulation of Cd, particularly throughout the wheat growth period. This experiment employed two different B fertilization methods. The soil application method utilized 1.5 mg B kg^-1 soil (Cd+B) and foliar application utilized 0.1% (F0.1%), 0.3% (F0.3%), and 0.6% (F0.6%) B concentrations along with 4 mg kg^-1 Cd. The results showed that B application in the soil reduced Cd concentrations per plant by 43.9% at the seedling stage, 74.59% in the roots, and 52.11% in the shoots at the elongation stage. At the same time, Cd concentrations in the roots were higher by B application at the anthesis and maturity stages, suggesting that B retains more Cd in the roots. The gray correlation analysis showed that the gray relational coefficients followed the following order: F0.3% > F0.1% > Cd+B > F0.6%. According to quantitative real-time PCR analysis, the six Cd transporters were mostly expressed in the roots at the seedling stage and anthesis stage. In addition, the expression of TCONS1113, TRIAE1060, and TRIAE5370 showed a negative correlation relationship with Cd concentration at the seedling stage, both in roots and shoots. At the anthesis stage, the expression of TCONS1113 and TRIAE5370 in roots was higher in Cd-treated plants compared to B-treated plants, and a similar tendency was noted for the expression of TRIAE5770 and TRIAE1060 in shoots as well. These results suggest that B application could significantly inhibit Cd uptake and translocation by regulating the expression of Cd transporter genes, especially at the seedling stage and the elongation phase in wheat.

Boron supplying alters cadmium retention in root cell walls and glutathione content in Capsicum annuum

Large areas of farmland in southern China are facing environmental problems such as cadmium (Cd) contamination and boron (B) deficiency. The aim of this study was to investigate the biochemical and molecular mechanisms underlying the reduction in Cd accumulation in hot pepper (Capsicum annuum) by B application. A hydroponic experiment was conducted to compare the subcellular distribution of Cd, transcriptome profile, degree of pectin methylation, and glutathione (GSH) synthesis in the roots of hot pepper under different B and Cd conditions. Boron supply promoted root cell wall biosynthesis and pectin demethylation by upregulating related genes and increasing cell wall Cd concentration by 28%. In addition, with the application of B, the proportion of Cd in root cell walls increased from 27% to 37%. Boron supplementation upregulated sulfur metabolism-related genes but decreased cysteine and GSH contents in the roots. As a result, shoot Cd concentration decreased by 27% due to the decrease in GSH, a critical long-distance transport carrier of Cd. Consequently, B supply could reduce the uptake, translocation, and accumulation of Cd in hot pepper by retaining Cd in the root cell walls and decreasing GSH content.

Citrus Physiological and Molecular Response to Boron Stresses

Since the essentiality of boron (B) to plant growth was reported nearly one century ago, the implication of B in physiological performance, productivity and quality of agricultural products, and the morphogenesis of apical meristem in plants has widely been studied. B stresses (B deficiency and toxicity), which lead to atrophy of canopy and deterioration of Citrus fruits, have long been discovered in citrus orchards. This paper reviews the research progress of B stresses on Citrus growth, photosynthesis, light use efficiency, nutrient absorption, organic acid metabolism, sugar metabolism and relocation, and antioxidant system. Moreover, the beneficial effects of B on plant stress tolerance and further research in this area were also discussed.

Molecular and biochemical mechanisms underlying boron-induced alleviation of cadmium toxicity in rice seedlings

Both cadmium (Cd) contamination and boron (B) deficiency in farmland soils pose a threat to the yield and quality of crops in Southern China. The present study investigated the mechanisms by which B reduces Cd accumulation in rice (Oryza sativa) seedlings. Boron supplementation partially restored the decline in shoot and root biomass caused by Cd treatment (26% and 33%, respectively), with no significant difference between the B+Cd and control groups. We also found that B significantly reduced shoot and root Cd concentrations (by 64% and 25%, respectively) but increased Cd concentration (by 43%) and proportion (from 38% to 55%) in root cell walls. Transcriptome analysis and biochemical tests suggested that B supplementation enhanced lignin and pectin biosynthesis, pectin demethylation, and sulfur and glutathione metabolism. Moreover, B decreased the expression of some Cd-induced transporter-related genes (i.e., HMA2, Nramp1, and several ABC genes). These results indicate that B relieved Cd toxicity and reduced Cd accumulation in rice seedlings by restraining Cd uptake and translocation from root to shoot by improving Cd tolerance and chelation ability. These novel findings would benefit further investigations into how B influences Cd uptake, translocation, detoxification, and accumulation in crops.