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Silicon (Si) is involved in the mitigation effect of plants to various environmental stresses. However, the mechanisms of aluminum (Al) detoxification by Si needs to be further clarified, especially in soybean. Here, the role of Si in the amelioration of programmed cell death (PCD) caused by Al exposure was explored in soybean roots. Results showed that supplying Si reduced the cell death, Hsr203J (a PCD marker gene) expression, mitochondrial cytochrome c release and caspase-3-like protease activity under Al stress, indicating that Si alleviated Al-induced PCD dependent on mitochondrial pathway. Exogenous H2O2 treatment could induce PCD of root tips exposed to Al, and applying Si reduced the production of H2O2 and O2−• in Al-treated roots, indicating that Si alleviated the occurrence of PCD by removing the accumulation of reactive oxygen species (ROS) under Al exposure. Furthermore, the activities of antioxidant enzymes and the contents of small molecule antioxidants were increased by applying Si under Al exposure. Overall, these results indicate that Si can eliminate Al-induced ROS accumulation and thus alleviate PCD by increasing the activity of antioxidant systems, which provides a theoretical basis for the improvement of crop growth in acid soils. [ABSTRACT FROM AUTHOR]

Silicon (Si) participates in the alleviation of plants to aluminum (Al) toxicity. However, the mechanisms of Al detoxification by Si needs to be further clarified, especially in soybean. We investigated the roles of citrate secretion and cell wall polysaccharides in Si-triggered soybean resistance to Al stress. Results showed that applying 2 mM Si alleviated elongation inhibition of soybean roots exposed to 100 or 200 µM Al for 24 h. Si application increased citrate exudation from roots under Al exposure, thereby reducing Al accumulation. Furthermore, Si promoted citrate synthesis through activating citrate synthase and inhibiting aconitase under Al stress. Quantitative real-time PCR assay showed that Si enhanced the expression level of citrate transporter genes (GmMATE13 and GmMATE47) under Al stress. In addition, Si supply reduced Al content in cell wall and in cell wall polysaccharides (pectin and hemicellulose 1) under Al exposure. Meanwhile, Si addition decreased the contents of pectin and hemicellulose 1, which were the main binding sites for Al in cell wall, under Al exposure. Furthermore, Si increased the degree of pectin methylesterification by inhibiting pectin methylesterase activity under Al stress, thereby reducing the ability of pectin to bind Al. These results suggest that Si can promote citrate efflux by regulating the synthesis and transport of citrate, thus chelating the toxic Al cations and alleviating Al toxicity. Besides, Si can also regulate the cell wall properties to reduce Al deposition in the cell wall of root tip, thereby improving Al tolerance of soybean. [ABSTRACT FROM AUTHOR]

Background and aims: "Astringent seed" is a type of abortive seed frequently observed in Chinese fir (Cunninghamia lanceolata). It is widely recognized but poorly understood for its underlying causes. This study investigates the potential of astringent seeds to alleviate the toxic effects of active aluminum ions. Methods: This study involved treating seeds and seedlings with two distinct concentrations of astringent seeds water extracts under the aluminum ion stress. Then the germination of seeds and growth of seedlings were evaluated and compared. Results: Under aluminum stress, both seed germination and seedling growth were notably inhibited. Treatment with a low-concentration of the extract significantly alleviated this inhibition. Root elongation in the seedlings increased by 36.95% compared to the control group, and the aluminum ion accumulation at the root tips was reduced by 38.89% relative to the aluminum-stressed group. This treatment also normalized the levels of malondialdehyde (MDA) in the roots and leaves, enhanced the activities of antioxidative enzymes such as superoxide dismutase (SOD) and catalase (CAT), and restored the levels of endogenous hormones including gibberellin (GA3), indole-3-acetic acid (IAA), methyl jasmonate (Ja-ME), and abscisic acid (ABA). Furthermore, the low-concentration of the extract positively impacted the disorganized chloroplast structures. In contrast, a high-concentration of the extract failed to revert most of these stress indicators. Conclusion: Low concentrations of astringent seed water extract effectively alleviate the inhibitory effects of aluminum ions on seed and seedling. This implies that in natural environments, the proximity of healthy seeds to astringent seeds could potentially enhance their growth. [ABSTRACT FROM AUTHOR]

Background : Aluminum (Al) toxicity poses a significant environmental stress factor, adversely affecting seed germination, crop establishment, quality, and production, primarily due to global soil acidification. Various methods have been explored to mitigate Al toxicity, either by excluding Al ions (Al3+) or accumulating them internally in plants. However, some methods have proven impractical due to their ineffectiveness and associated environmental hazards. Examining discoveries about these pathways is critical for capturing the state-of-the-art of the Al3+ response in plants, highlighting major findings, identifying research gaps, and posing new questions. Scope: In this review, we discuss the past and current knowledge about the relationship between subcellular Al distribution and differential cell ultrastructure. We also explore environmentally friendly approaches that can effectively alleviate Al toxicity in both soil and plants. Beneficial effects of microorganisms on plants exposed to Al3+ stress are discussed, as well as bioaugmentation approaches, involving the addition of microbial cultures or genetically engineered organisms to accelerate the rate of Al contaminant breakdown in the soil. Conclusion: Our coverage highlights upcoming studies that concentrate on exploring inter- and intraspecies variations in plant responses to Al stress. To enhance our understanding and pave the way for new molecular breeding targets to improve plant performance under Al stress, staying abreast of current and future insights into how plants adapt to Al stress is imperative. [ABSTRACT FROM AUTHOR]

The widespread occurrence of acidic soils presents a major challenge for agriculture, as it hampers productivity via a combination of mineral toxicity, nutrient deficiency, and poor water uptake. Conventional remediation methods, such as amending the soil with lime, magnesium, or calcium, are expensive and not environmentally friendly. The most effective method to mitigate soil acidity is the cultivation of acid-tolerant cultivars. The ability of plants to tolerate acidic soils varies significantly, and a key factor influencing this tolerance is aluminum (Al) toxicity. Therefore, understanding the physiological, molecular, and genetic underpinnings of Al tolerance is essential for the successful breeding of acid-tolerant crops. Different tolerance mechanisms are regulated by various genes and quantitative trait loci in various plant species, and molecular markers have been developed to facilitate gene cloning and to support marker-assisted selection for breeding Al-tolerant cultivars. This study provides a comprehensive review of the current developments in understanding the physiological and molecular mechanisms underlying Al resistance. Through the application of genome-wide association methods, it is expected that new Al-resistant genes can be identified and utilized to cultivate Al-resistant varieties through intercrossing, backcrossing, and molecular marker-assisted selection, promoting the sustainable use of acidic soils. [ABSTRACT FROM AUTHOR]

Due to climate change, water deficits (WDs) and aluminum (Al) toxicity are increasing, affecting plants, especially crops such as blueberries (Vaccinium corymbosum L.). The application of methyl jasmonate (MeJA) could mitigate these effects. This work aimed to evaluate the effective MeJA dose to overcome oxidative stress provoked by combined WD+Al stress in blueberries. Plants of Al-sensitive (Star) and Al-resistant (Legacy) cultivars were exposed to control (Al at 65 mg/Kg, 80% field capacity), WD+Al (50% field capacity; Al at 1665 mg/Kg), and WD+Al treatment with different foliar MeJA doses (10, 50, and 100 μM) during 7 and 21 days. Data revealed that plants exposed to WD+Al and treated with 50 µM MeJA reduced Al up to 3.2-fold in roots and 2.7-fold in leaves and improved water potential (Ψw) up to 2.5-fold. The sensitive cultivar decreased the relative growth rate under WD+Al, increasing by 1.9-fold with 50 µM MeJA. Under WD+Al stress, all MeJA doses mitigated the decrease in relative water content in Al-resistant cultivars, restoring values like control plants. In the sensitive cultivar, 50 µM MeJA increased photosynthesis (1.5-fold) and stomatal conductance (1.4-fold), without changes in transpiration. Lipid peroxidation decreased (1.2-fold) and increased antioxidant activity (1.8-fold), total phenols (1.6-fold), and superoxide dismutase activity (3.3-fold) under WD+Al and 50 µM-MeJA. It was concluded that the most effective dose to alleviate the WD+Al stress was 50 µM MeJA due to the activation of antioxidants in blueberry plants. Therefore, the MeJA application could be a potential strategy for enhancing the resilience of V. corynbosum exposed to WD+Al stress. [ABSTRACT FROM AUTHOR]

Soil acidification and low nutrient availability are two major challenges facing agriculture in most regions of East Africa, resulting in aluminum toxicity and poor crop yields. The amendment of local sediments to cropland can potentially alleviate these challenges, but responses are variable. In this study, we investigated the potential of two different local sediments influenced by volcanic deposits to increase soil pH, Si and P availability and reduce Al toxicity, thereby improve barley yield. Hence, a field experiment was established in Eldoret, Western Kenya, using 1% and 3% addition by weight of two sediments in barley cultivated plots. The Baringo 3% amendment significantly increased soil pH (from 4.7 to 7.0), the available P content (from 0.01 mg g-1 to 0.02 mg g-1) and decreased the Al availability (from 3.03 mg g-1--2.17 mg g-1). This resulted in a barley yield of 4.7 t/ha (+1061%). The Nakuru 3% and Baringo 1% amendments increased yield to 2--3 t/ha, while the Nakuru 1% did not significantly increase yield. These results highlight that, from a biophysical perspective, there are natural and local opportunities to reduce soil acidification and to partly replace mineral fertilizer, but its magnitude depends on the sediment and the amendment rate. [ABSTRACT FROM AUTHOR]

Summary: The primary mechanisms contributing to nitrogen (N) addition induced grassland biodiversity loss, namely light competition and soil cation toxicity, are often examined separately in various studies. However, their relative significance in governing biodiversity loss along N addition gradient remains unclear.We conducted a 4‐yr field experiment with five N addition rates (0, 2, 10, 20, and 50 g N m−2 yr−1) and performed a meta‐analysis using global data from 239 observations in N‐fertilized grassland ecosystems.Results from our field experiment and meta‐analysis indicate that both light competition and soil cation (e.g. Mn2+ and Al3+) toxicity contribute to plant diversity loss under N enrichment. The relative importance of these mechanisms varied with N enrichment intensity. Light competition played a more significant role in influencing species richness under low N addition (≤ 10 g m−2 yr−1), while cation toxicity became increasingly dominant in reducing biodiversity under high N addition (>10 g m−2 yr−1). Therefore, a transition from light competition to cation toxicity occurs with increasing N availability.These findings imply that the biodiversity loss along the N gradient is regulated by distinct mechanisms, necessitating the adoption of differential management strategies to mitigate diversity loss under varying intensities of N enrichment. [ABSTRACT FROM AUTHOR]

Sophora davidii, a vital forage species, predominantly thrives in the subtropical karst mountains of Southwest China. Its resilience to poor soil conditions and arid environments renders it an ideal pioneer species for ecological restoration in these regions. This study investigates the influence of acidic, aluminum-rich local soil on the germination and seedling growth physiology of S. davidii. Experiments were conducted under varying degrees of acidity and aluminum stress, employing three pH levels (3.5 to 5.5) and four aluminum concentrations (0.5 to 2.0 mmol·L−1). The results showed that germination rate, germination index, and vigor index of S. davidii seeds were decreased but not significantly under slightly acidic conditions (pH 4.5–5.5), while strong acid (pH = 3.5) significantly inhibited the germination rate, germination index, and vigor index of white spurge seeds compared with the control group. Aluminum stress (≥0.5 mmol·L−1) significantly inhibited the germination rate, germination index, and vigor index of S. davidii seed. Moreover, the seedlings’ root systems were sensitive to the changes of aluminum concentration, evident from significant root growth inhibition, characterized by root shortening and color deepening. Notably, under aluminum stress (pH = 4.3), the levels of malondialdehyde and proline in S. davidii escalated with increasing aluminum concentration, while antioxidant enzyme activities demonstrated an initial increase followed by a decline. The study underscores the pivotal role of cellular osmoregulatory substances and protective enzymes in combating aluminum toxicity in S. davidii, a key factor exacerbating growth inhibition in acidic environments. These findings offer preliminary theoretical insights for the practical agricultural utilization of S. davidii in challenging soil conditions.

Aluminum (Al), prevalent in the crust of the Earth, jeopardizes plant health in acidic soils, hindering root growth and overall development. In this study, we first analysed the Al- and pH- tolerance of the Penicillium olsonii TLL1 strain (POT1; NRRL:68252) and investigated the potential for enhancing plant resilience under Al-rich acidic soil conditions. Our research illustrates the extraordinary tolerance of POT1 to both high Al concentrations and acidic conditions, showcasing its potential to alleviate Al-induced stress in plants. Metabolite analysis revealed that POT1 detoxifies Al through organic acid-dependent chelation mechanisms, significantly reducing Al stress in Arabidopsis and Pak Choi plants. Consequently, plant growth conditions improved, and the Al content in plant tissues decreased. Transcriptome analysis indicated that POT1 treatment downregulates genes associated with Al and oxidative stress such as MATE, ALS3, NIP1--2 and several peroxidases, highlighting its effectiveness in lessening Al-induced damage. Comparative assessments highlight the superior performance of POT1 compared to other Al-tolerant Penicillium species, attributed to its ability to thrive in diverse pH levels and effectively detoxify Al. These findings position POT1 as a promising agent for enhancing crop resilience in Al-compromised acidic soils, offering new avenues for promoting plant health and bolstering food security through increased crop yield and safety. [ABSTRACT FROM AUTHOR]

Key message: AcEXPA1, an aluminum (Al)-inducible expansin gene, is demonstrated to be involved in carpetgrass (Axonopus compressus) root elongation under Al toxicity through analyzing composite carpetgrass plants overexpressing AcEXPA1. Aluminum (Al) toxicity is a major mineral toxicity that limits plant productivity in acidic soils by inhibiting root growth. Carpetgrass (Axonopus compressus), a dominant warm-season turfgrass widely grown in acidic tropical soils, exhibits superior adaptability to Al toxicity. However, the mechanisms underlying its Al tolerance are largely unclear, and knowledge of the functional genes involved in Al detoxification in this turfgrass is limited. In this study, phenotypic variation in Al tolerance, as indicated by relative root elongation, was observed among seventeen carpetgrass genotypes. Al-responsive genes related to cell wall modification were identified in the roots of the Al-tolerant genotype ‘A58’ via transcriptome analysis. Among them, a gene encoding α-expansin was cloned and designated AcEXPA1 for functional characterization. Observed Al dose effects and temporal responses revealed that Al induced AcEXPA1 expression in carpetgrass roots. Subsequently, an efficient and convenient Agrobacterium rhizogenes-mediated transformation method was established to generate composite carpetgrass plants with transgenic hairy roots for investigating AcEXPA1 involvement in carpetgrass root growth under Al toxicity. AcEXPA1 was successfully overexpressed in the transgenic hairy roots, and AcEXPA1 overexpression enhanced Al tolerance in composite carpetgrass plants through a decrease in Al-induced root growth inhibition. Taken together, these findings suggest that AcEXPA1 contributes to Al tolerance in carpetgrass via root growth regulation. [ABSTRACT FROM AUTHOR]

Background and aims“Astringent seed” is a type of abortive seed frequently observed in Chinese fir (Cunninghamia lanceolata). It is widely recognized but poorly understood for its underlying causes. This study investigates the potential of astringent seeds to alleviate the toxic effects of active aluminum ions.MethodsThis study involved treating seeds and seedlings with two distinct concentrations of astringent seeds water extracts under the aluminum ion stress. Then the germination of seeds and growth of seedlings were evaluated and compared.ResultsUnder aluminum stress, both seed germination and seedling growth were notably inhibited. Treatment with a low-concentration of the extract significantly alleviated this inhibition. Root elongation in the seedlings increased by 36.95% compared to the control group, and the aluminum ion accumulation at the root tips was reduced by 38.89% relative to the aluminum-stressed group. This treatment also normalized the levels of malondialdehyde (MDA) in the roots and leaves, enhanced the activities of antioxidative enzymes such as superoxide dismutase (SOD) and catalase (CAT), and restored the levels of endogenous hormones including gibberellin (GA3), indole-3-acetic acid (IAA), methyl jasmonate (Ja-ME), and abscisic acid (ABA). Furthermore, the low-concentration of the extract positively impacted the disorganized chloroplast structures. In contrast, a high-concentration of the extract failed to revert most of these stress indicators.ConclusionLow concentrations of astringent seed water extract effectively alleviate the inhibitory effects of aluminum ions on seed and seedling. This implies that in natural environments, the proximity of healthy seeds to astringent seeds could potentially enhance their growth.

Soil acidification and low nutrient availability are two major challenges facing agriculture in most regions of East Africa, resulting in aluminum toxicity and poor crop yields. The amendment of local sediments to cropland can potentially alleviate these challenges, but responses are variable. In this study, we investigated the potential of two different local sediments influenced by volcanic deposits to increase soil pH, Si and P availability and reduce Al toxicity, thereby improve barley yield. Hence, a field experiment was established in Eldoret, Western Kenya, using 1% and 3% addition by weight of two sediments in barley cultivated plots. The Baringo 3% amendment significantly increased soil pH (from 4.7 to 7.0), the available P content (from 0.01 mg g−1 to 0.02 mg g−1) and decreased the Al availability (from 3.03 mg g−1–2.17 mg g−1). This resulted in a barley yield of 4.7 t/ha (+1061%). The Nakuru 3% and Baringo 1% amendments increased yield to 2–3 t/ha, while the Nakuru 1% did not significantly increase yield. These results highlight that, from a biophysical perspective, there are natural and local opportunities to reduce soil acidification and to partly replace mineral fertilizer, but its magnitude depends on the sediment and the amendment rate.

Aluminum (Al) toxicity poses a significant challenge to agricultural productivity, particularly in acidic soils. The banana crop, predominantly cultivated in tropical and subtropical climates, often grapples with low pH and Al toxicity. This study seeks to explore the differential responses of two banana genotypes with varying Al tolerance (Baodao and Baxi) to Al exposure (100 and 500 µM) for 24 h. Microscopic analysis uncovered distinctive structural modifications in root cells, with Baodao displaying more severe alterations in response to Al stress. There was higher superoxide (O2−.) and hydrogen peroxide (H2O2) production and lipid peroxidation in Baodao indicating enhanced oxidative stress and membrane damage. Al accumulation in root tips was higher in Baxi than Baodao, while the roots of Baodao had a higher accumulation of callose. Nutrient content analysis revealed alterations in ion levels, highlighting the impact of Al exposure on nutrient uptake and homeostasis. In summary, Al differentially affects callose deposition, which, in turn, leads to Al uptake and nutrient homeostasis alteration in two contrasting banana genotypes. This intricate interplay is a key factor in understanding plant responses to aluminum toxicity and can inform strategies for crop improvement and soil management in aluminum-stressed environments. [ABSTRACT FROM AUTHOR]

Aluminum chloride (AlCl3) is a potent neurotoxic substance known to cause memory impairment and oxidative stress‐dependent neurodegeneration. Naringenin (NAR) is a dietary flavonoid with potent antioxidant and anti‐inflammatory properties which was implemented against AlCl3‐induced neurotoxicity to ascertain its neuroprotective efficacy. Experimental neurotoxicity in mice was induced by exposure of AlCl3 (10 mg/kg, p.o.) followed by treatment with NAR (10 mg/kg, p.o.) for a total of 63 days. Assessed the morphometric, learning memory dysfunction (novel object recognition, T‐ and Y‐maze tests), neuronal oxidative stress, and histopathological alteration in different regions of the brain, mainly cortex, hippocampus, thalamus, and cerebellum. AlCl3 significantly suppressed the spatial learning and memory power which were notably improved by administration of NAR. The levels of oxidative stress parameters nitric oxide, advanced oxidation of protein products, protein carbonylation, lipid peroxidation, superoxide dismutase, catalase, glutathione reductase, reduced glutathione, and the activity of acetylcholine esterase were altered 1.5–3 folds by AlCl3 significantly. Treatment of NAR remarkably restored the level of oxidative stress parameters and maintained the antioxidant defense system. AlCl3 suppressed the expression of neuronal proliferation marker NeuN that was restored by NAR treatment which may be a plausible mechanism. NAR showed therapeutic efficacy as a natural supplement against aluminum‐intoxicated memory impairments and histopathological alteration through a mechanism involving an antioxidant defense system and neuronal proliferation. [ABSTRACT FROM AUTHOR]

Excessive aluminum (Al) in acidic soils is a primary factor that hinders plant growth. The objective of the present study was to investigate the effect and physiological mechanism of exogenous silicon (Si) in alleviating aluminum toxicity. Under hydroponic conditions, 4 mM Al significantly impeded the growth of white clover; however, pretreatments with 1 mM Si mitigated this inhibition, as evidenced by notable changes in growth indicators and physiological parameters. Exogenous silicon notably increased both shoot and root length of white clover and significantly decreased electrolyte leakage (EL) and malondialdehyde (MDA) content compared to aluminum treatments. This positive effect was particularly evident in the roots. Further analysis involving hematoxylin staining, scanning electron microscopy (SEM), and examination of organic acids (OAs) demonstrated that silicon relieved the accumulation of bioactive aluminum and ameliorated damage to root tissues in aluminum-stressed plants. Additionally, energy-dispersive X-ray (EDX) analysis revealed that additional silicon was primarily distributed in the root epidermal and cortical layers, effectively reducing the transport of aluminum and maintaining the balance of exchangeable cations absorption. These findings suggest that gradual silicon deposition in root tissues effectively prevents the absorption of biologically active aluminum, thereby reducing the risk of mineral nutrient deficiencies induced by aluminum stress, promoting organic acids exudation, and compartmentalizing aluminum in the outer layer of root tissues. This mechanism helps white clover alleviate the damage caused by aluminum toxicity. [ABSTRACT FROM AUTHOR]

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Aluminum (Al) toxicity and phosphorus (P) deficiency are widely recognized as major constraints to agricultural productivity in acidic soils. Under this scenario, the development of ryegrass plants with enhanced P use efficiency and Al resistance is a promising approach by which to maintain pasture production. In this study, we assessed the contribution of growth traits, P efficiency, organic acid anion (OA) exudation, and the expression of Al-responsive genes in improving tolerance to concurrent low-P and Al stress in ryegrass (Lolium perenne L.). Ryegrass plants were hydroponically grown under optimal (0.1 mM) or low-P (0.01 mM) conditions for 21 days, and further supplied with Al (0 and 0.2 mM) for 3 h, 24 h and 7 days. Accordingly, higher Al accumulation in the roots and lower Al translocation to the shoots were found in ryegrass exposed to both stresses. Aluminum toxicity and P limitation did not change the OA exudation pattern exhibited by roots. However, an improvement in the root growth traits and P accumulation was found, suggesting an enhancement in Al tolerance and P efficiency under combined Al and low-P stress. Al-responsive genes were highly upregulated by Al stress and P limitation, and also closely related to P utilization efficiency. Overall, our results provide evidence of the specific strategies used by ryegrass to co-adapt to multiple stresses in acid soils. [ABSTRACT FROM AUTHOR]

The toxicity of aluminum (Al) in acidic soil inhibits plant root development and reduces crop yields. In the plant response to Al toxicity, the initiation of programmed cell death (PCD) appears to be an important mechanism for the elimination of Al-damaged cells to ensure plant survival. In a previous study, the type I metacaspase AhMC1 was found to regulate the Al stress response and to be essential for Al-induced PCD. However, the mechanism by which AhMC1 is altered in the peanut response to Al stress remained unclear. Here, we show that a nuclear protein, mutator-like transposable element 9A (AhMULE9A), directly interacts with AhMC1 in vitro and in vivo. This interaction occurs in the nucleus in peanut and is weakened during Al stress. Furthermore, a conserved C2HC zinc finger domain of AhMULE9A (residues 735–751) was shown to be required for its interaction with AhMC1. Overexpression of AhMULE9A in Arabidopsis and peanut strongly inhibited root growth with a loss of root cell viability under Al treatment. Conversely, knock down of AhMULE9A in peanut significantly reduced Al uptake and Al inhibition of root growth, and alleviated the occurrence of typical hallmarks of Al-induced PCD. These findings provide novel insight into the regulation of Al-induced PCD. [ABSTRACT FROM AUTHOR]

Isoprenoid metabolism and its derivatives took part in photosynthesis, growth regulation, signal transduction, and plant defense to biotic and abiotic stresses. However, how aluminum (Al) stress affects the isoprenoid metabolism and whether isoprenoid metabolism plays a vital role in the Citrus plants in coping with Al stress remain unclear. In this study, we reported that Al–treatment–induced alternation in the volatilization rate of monoterpenes (α–pinene, β–pinene, limonene, α–terpinene, γ–terpinene and 3–carene) and isoprene were different between Citrus sinensis (Al-tolerant) and C. grandis (Al-sensitive) leaves. The Al-induced decrease of CO2 assimilation, maximum quantum yield of primary PSII photochemistry (Fv/Fm), the lower contents of glucose and starch, and the lowered activities of enzymes involved in the mevalonic acid (MVA) pathway and 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway might account for the different volatilization rate of isoprenoids. Furthermore, the altered transcript levels of genes related to isoprenoid precursors and/or derivatives metabolism, such as geranyl diphosphate (GPP) synthase (GPPS) in GPP biosynthesis, geranylgeranyl diphosphate synthase (GGPPS), chlorophyll synthase (CHS) and GGPP reductase (GGPPR) in chlorophyll biosynthesis, limonene synthase (LS) and α-pinene synthase (APS) in limonene and α–pinene synthesis, respectively, might be responsible for the different contents of corresponding products in C. grandis and C. sinensis. Our data suggested that isoprenoid metabolism was involved in Al tolerance response in Citrus, and the alternation of some branches of isoprenoid metabolism could confer different Al-tolerance to Citrus species.

Aluminum (Al), prevalent in the crust of the Earth, jeopardizes plant health in acidic soils, hindering root growth and overall development. In this study, we first analysed the Al- and pH- tolerance of the Penicillium olsonii TLL1 strain (POT1; NRRL:68252) and investigated the potential for enhancing plant resilience under Al-rich acidic soil conditions. Our research illustrates the extraordinary tolerance of POT1 to both high Al concentrations and acidic conditions, showcasing its potential to alleviate Al-induced stress in plants. Metabolite analysis revealed that POT1 detoxifies Al through organic acid-dependent chelation mechanisms, significantly reducing Al stress in Arabidopsis and Pak Choi plants. Consequently, plant growth conditions improved, and the Al content in plant tissues decreased. Transcriptome analysis indicated that POT1 treatment downregulates genes associated with Al and oxidative stress such as MATE, ALS3, NIP1–2 and several peroxidases, highlighting its effectiveness in lessening Al-induced damage. Comparative assessments highlight the superior performance of POT1 compared to other Al-tolerant Penicillium species, attributed to its ability to thrive in diverse pH levels and effectively detoxify Al. These findings position POT1 as a promising agent for enhancing crop resilience in Al-compromised acidic soils, offering new avenues for promoting plant health and bolstering food security through increased crop yield and safety.

Due to climate change, water deficits (WDs) and aluminum (Al) toxicity are increasing, affecting plants, especially crops such as blueberries (Vaccinium corymbosum L.). The application of methyl jasmonate (MeJA) could mitigate these effects. This work aimed to evaluate the effective MeJA dose to overcome oxidative stress provoked by combined WD+Al stress in blueberries. Plants of Al-sensitive (Star) and Al-resistant (Legacy) cultivars were exposed to control (Al at 65 mg/Kg, 80% field capacity), WD+Al (50% field capacity; Al at 1665 mg/Kg), and WD+Al treatment with different foliar MeJA doses (10, 50, and 100 μM) during 7 and 21 days. Data revealed that plants exposed to WD+Al and treated with 50 µM MeJA reduced Al up to 3.2-fold in roots and 2.7-fold in leaves and improved water potential (Ψw) up to 2.5-fold. The sensitive cultivar decreased the relative growth rate under WD+Al, increasing by 1.9-fold with 50 µM MeJA. Under WD+Al stress, all MeJA doses mitigated the decrease in relative water content in Al-resistant cultivars, restoring values like control plants. In the sensitive cultivar, 50 µM MeJA increased photosynthesis (1.5-fold) and stomatal conductance (1.4-fold), without changes in transpiration. Lipid peroxidation decreased (1.2-fold) and increased antioxidant activity (1.8-fold), total phenols (1.6-fold), and superoxide dismutase activity (3.3-fold) under WD+Al and 50 µM-MeJA. It was concluded that the most effective dose to alleviate the WD+Al stress was 50 µM MeJA due to the activation of antioxidants in blueberry plants. Therefore, the MeJA application could be a potential strategy for enhancing the resilience of V. corynbosum exposed to WD+Al stress.

Excessive aluminum (Al) in acidic soils is a primary factor that hinders plant growth. The objective of the present study was to investigate the effect and physiological mechanism of exogenous silicon (Si) in alleviating aluminum toxicity. Under hydroponic conditions, 4 mM Al significantly impeded the growth of white clover; however, pretreatments with 1 mM Si mitigated this inhibition, as evidenced by notable changes in growth indicators and physiological parameters. Exogenous silicon notably increased both shoot and root length of white clover and significantly decreased electrolyte leakage (EL) and malondialdehyde (MDA) content compared to aluminum treatments. This positive effect was particularly evident in the roots. Further analysis involving hematoxylin staining, scanning electron microscopy (SEM), and examination of organic acids (OAs) demonstrated that silicon relieved the accumulation of bioactive aluminum and ameliorated damage to root tissues in aluminum-stressed plants. Additionally, energy-dispersive X-ray (EDX) analysis revealed that additional silicon was primarily distributed in the root epidermal and cortical layers, effectively reducing the transport of aluminum and maintaining the balance of exchangeable cations absorption. These findings suggest that gradual silicon deposition in root tissues effectively prevents the absorption of biologically active aluminum, thereby reducing the risk of mineral nutrient deficiencies induced by aluminum stress, promoting organic acids exudation, and compartmentalizing aluminum in the outer layer of root tissues. This mechanism helps white clover alleviate the damage caused by aluminum toxicity.

ABSTRACT Peach rootstock and scion cultivars are selected in breeding programs considering resistance to pests and diseases, salt tolerance, drought tolerance, and vigor. However, rootstock tolerance to aluminum (Al), which is markedly present in tropical and subtropical soils of the world, is not considered. Thus, it is essential to define potential markers that can contribute to the selection of Al-resistant or Al-tolerant peach rootstocks. The objective of this study was to identify Al-tolerant peach tree rootstock cultivars and clonal selections using physiological and oxidative stress variables. A completely randomized experimental design was used in a 13 (rootstock cultivars and clonal selections) × 2 (with and without Al) factorial arrangement, with three replications. Nursery peach trees of own-rooted ‘BRS Mandinho’ (without rootstock) and nursery trees of ‘BRS Mandinho’ grafted on different rootstock cultivars and clonal selections were grown in a hydroponic system, consisting of two treatments, with and without 100 mg L-1 of Al. Dry biomass, photosynthetic variables, pigment concentration, hydrogen peroxide content, membrane lipid peroxidation, and activity of the antioxidant enzymes were evaluated. The total dry matter production of the own-rooted ‘BRS Mandinho’ trees and the SS-CHI-09-39 and SS-CHI-09-40 selections is affected by the Al presence, representing a decline of 35.4, 37.2, and 24.4 %, respectively, compared to the treatment with Al. The highest total dry matter production in Al presence was observed for the ‘Sharpe’ rootstock. ‘Capdeboscq’, DB-SEN-09-23, FB-ESM-09-43, JB-ESM-09-13, JAH-MAC-09-77, SAS-SAU-09-71, and VEH-GRA-09-55 rootstock selections are tolerant to Al. The use of physiological and biochemical variables shows potential for the selection of clonal rootstocks tolerant or resistant to Al.

Aluminum toxicity poses a significant constraint on crop production in acidic soils. While phytohormones are recognized for their pivotal role in mediating plant responses to aluminum stress, the specific involvement of gibberellin (GA) in regulating aluminum tolerance remains unexplored. In this study, we demonstrate that external GA exacerbates the inhibitory impact of aluminum stress on root growth of rice seedlings, concurrently promoting reactive oxygen species (ROS) accumulation. Furthermore, rice plants overexpressing the GA synthesis gene SD1 exhibit enhanced sensitivity to aluminum stress. In contrast, the slr1 gain-of-function mutant, characterized by impeded GA signaling, displays enhanced tolerance to aluminum stress, suggesting the negative regulatory role of GA in rice resistance to aluminum-induced toxicity. We also reveal that GA application suppresses the expression of crucial aluminum tolerance genes in rice, including Al resistance transcription factor 1 (ART1), Nramp aluminum transporter 1 (OsNramp4), and Sensitive to Aluminum 1 (SAL1). Conversely, the slr1 mutant exhibits up-regulated expression of these genes compared to the wild type. In summary, our results shed light on the inhibitory effect of GA in rice resistance to aluminum stress, contributing to a theoretical foundation for unraveling the intricate mechanisms of plant hormones in regulating aluminum tolerance. [ABSTRACT FROM AUTHOR]

Winter canola (Brassica napus L.) is a potential alternative to winter wheat in Oklahoma rotation systems as a means to overcome the negative impacts of continuous wheat systems. However, its performance may suffer in the acid soils that are common to intensive agriculture systems in the southern Great Plains region. The objective of this study was to quantify the impact of soil pH and Al3+ concentration on winter canola production. Two field trials were conducted in 2016 and 2017 across four different locations in central Oklahoma to evaluate the performance of four canola cultivars in soils with a range of pH from 4.0 to 8.0. Yield, soil pH, and Al3+ concentrations were measured from each plot to study the relationships between these variables. At all but one location, soil pH and Al3+ concentrations were inversely related and when data across these locations were combined, Al3+ concentrations decreased as pH increased to a critical value of 4.8 (r² = 0.83). In general, it was found that yield decreased linearly as pH decreased below 5.8 (r² = 0.75) and increased linearly as Al3+ concentrations decreased below 87 mg kg-1 (r² = 0.73). Above these thresholds, yield was unrelated to pH or Al3+ concentrations. It was also observed that at one location with very low naturally occurring Al3+, high canola yields were achievable even in low soil pH. Therefore, Al3+ concentrations may be a better indicator of the effects of acidic soils on winter canola yields than pH values alone. [ABSTRACT FROM AUTHOR]

Acid soils occupy approximately 50% of potentially arable lands. Improving crop productivity in acid soils, therefore, will be crucial for ensuring food security and agricultural sustainability. High soil acidity often coexists with phosphorus (P) deficiency and aluminum (Al) toxicity, a combination that severely impedes crop growth and yield across wide areas. As roots explore soil for the nutrients and water required for plant growth and development, they also sense and respond to below-ground stresses. Within the terrestrial context of widespread P deficiency and Al toxicity pressures, plants, particularly roots, have evolved a variety of mechanisms for adapting to these stresses. As legumes, soybean (Glycine max) plants may acquire nitrogen (N) through symbiotic nitrogen fixation (SNF), an adaptation that can be useful for mitigating excessive N fertilizer use, either directly as leguminous crop participants in rotation and intercropping systems, or secondarily as green manure cover crops. In this review, we investigate legumes, especially soybean, for recent advances in our understanding of root-based mechanisms linked with root architecture modification, exudation and symbiosis, together with associated genetic and molecular strategies in adaptation to individual and/or interacting P and Al conditions in acid soils. We propose that breeding legume cultivars with superior nutrient efficiency and/or Al tolerance traits through genetic selection might become a potentially powerful strategy for producing crop varieties capable of maintaining or improving yields in more stressful soil conditions subjected to increasingly challenging environmental conditions.

Aluminum (Al), a non-essential metal for plant growth, exerts significant phytotoxic effects, particularly on root growth. Anthropogenic activities would intensify Al’s toxic effects by releasing Al3+ into the soil solution, especially in acidic soils with a pH lower than 5.5 and rich mineral content. The severity of Al-induced phytotoxicity varies based on factors such as Al concentration, ionic form, plant species, and growth stages. Al toxicity leads to inhibited root and shoot growth, reduced plant biomass, disrupted water uptake causing nutritional imbalance, and adverse alterations in physiological, biochemical, and molecular processes. These effects collectively lead to diminished plant yield and quality, along with reduced soil fertility. Plants employ various mechanisms to counter Al toxicity under stress conditions, including sequestering Al in vacuoles, exuding organic acids (OAs) like citrate, oxalate, and malate from root tip cells to form Al-complexes, activating antioxidative enzymes, and overexpressing Al-stress regulatory genes. Recent advancements focus on enhancing the exudation of OAs to prevent Al from entering the plant, and developing Al-tolerant varieties. Gene transporter families, such as ATP-Binding Cassette (ABC), Aluminum-activated Malate Transporter (ALMT), Natural resistance-associated macrophage protein (Nramp), Multidrug and Toxic compounds Extrusion (MATE), and aquaporin, play a crucial role in regulating Al toxicity. This comprehensive review examined recent progress in understanding the cytotoxic impact of Al on plants at the cellular and molecular levels. Diverse strategies developed by both plants and scientists to mitigate Al-induced phytotoxicity were discussed. Furthermore, the review explored recent genomic developments, identifying candidate genes responsible for OAs exudation, and delved into genome-mediated breeding initiatives, isolating transgenic and advanced breeding lines to cultivate Al-tolerant plants.

Biomineralization in plant roots refers to the process of cell-induced self-assembly to form nanostructures on the root surface. Silicon (Si) is the second most abundant element in soils, and beneficial to plant growth. Meanwhile, silicon is shown to participate in the process of biomineralization, which is useful for improving mechanical strength and alleviating biotic and abiotic stress, for example silicic acid polymerizes to form amorphous silica (SiO2–nH2O) in the process of growing to resist fungi and environmental stress. This process alters physical and chemical properties of cell wall. However, the mechanistic basis of this process remains unclear. Aluminum toxicity is a major constraint affecting plant performance in acid soil. This paper summarizes recent research advances in the field of plant biomineralization and describes the effects of silicon biomineralization on plant aluminum tolerance and its adaptive significance, using aluminum toxicity as a case study.

Aluminum (Al) toxicity and low pH are major factors limiting plant growth in acidic soils. Sensitive to Proton Rhizotoxicity 1 (STOP1) transcription factors respond to these stresses by regulating the expression of multiple Al- or low pH-responsive genes. ZmSTOP1-A, a STOP1-like protein from maize (Zea mays), was localized to the nucleus and showed transactivation activity. ZmSTOP1-A was expressed moderately in both roots and shoots of maize seedlings, but was not induced by Al stress or low pH. Overexpression of ZmSTOP1-A in Arabidopsis Atstop1 mutant partially restored Al tolerance and improved low pH tolerance with respect to root growth. Regarding Al tolerance, ZmSTOP1-A/Atstop1 plants showed clear upregulation of organic acid transporter genes, leading to increased organic acid secretion and reduced Al accumulation in roots. In addition, the antioxidant enzyme activity in roots and shoots of ZmSTOP1-A/Atstop1 plants was significantly enhanced, ultimately alleviating Al toxicity via scavenging reactive oxygen species. Similarly, ZmSTOP1-A could directly activate ZmMATE1 expression in maize, positively correlated with the number of Al-responsive GGNVS cis-elements in the ZmMATE1 promoter. Our results reveal that ZmSTOP1-A is an important transcription factor conferring Al tolerance by enhancing organic acid secretion and reactive oxygen species scavenging in Arabidopsis. [ABSTRACT FROM AUTHOR]

Centipedegrass (Eremochloa ophiuroides (Munro.) Hack.) is a species originating in China and is an excellent warm-season turfgrass. As a native species in southern China, it is naturally distributed in the phosphorus-deficient and aluminum-toxic acid soil areas. It is important to research the molecular mechanism of centipedegrass responses to phosphorus-deficiency and/or aluminum-toxicity stress. Quantitative Real-Time PCR (qRT-PCR) is a common method for gene expression analysis, and the accuracy of qRT-PCR results depends heavily on the stability of internal reference genes. However, there are still no reported stable and effective reference genes for qRT-PCR analysis of target genes under the acid-soil-related stresses in different organs of centipedegrass. For scientific rigor, the gene used as a reference for any plant species and/or any stress conditions should be first systematically screened and evaluated. This study is the first to provide a group of reliable reference genes to quantify the expression levels of functional genes of Eremochloa ophiuroides under multiple stresses of P deficiency and/or aluminum toxicity. In this study, centipedegrass seedlings of the acid-soil-resistant strain 'E041' and acid-soil-sensitive strain 'E089' were used for qRT-PCR analysis. A total of 11 candidate reference genes (ACT, TUB, GAPDH, TIP41, CACS, HNR, EP, EF1α, EIF4α, PP2A and actin) were detected by qRT-PCR technology, and the stability of candidate genes was evaluated with the combination of four internal stability analysis software programs. The candidate reference genes exhibited differential stability of expression in roots, stems and leaves under phosphorus-deficiency and/or aluminum-toxicity stress. On the whole, the results showed that GAPDH, TIP41 and HNR were the most stable in the total of samples. In addition, for different tissues under various stresses, the selected reference genes were also different. CACS and PP2A were identified as two stable reference genes in roots through all three stress treatments (phosphate deficiency, aluminum toxicity, and the multiple stress treatment of aluminum toxicity and phosphate deficiency). Moreover, CACS was also stable as a reference gene in roots under each treatment (phosphate deficiency, aluminum toxicity, or multiple stresses of aluminum toxicity and phosphate deficiency). In stems under all three stress treatments, GAPDH and EIF4α were the most stable reference genes; for leaves, PP2A and TIP41 showed the two highest rankings in all three stress treatments. Finally, qRT-PCR analysis of the expression patterns of the target gene ALMT1 was performed to verify the selected reference genes. The application of the reference genes identified as internal controls for qRT-PCR analysis will enable accurate analysis of the target gene expression levels and expression patterns in centipedegrass under acid-soil-related stresses. [ABSTRACT FROM AUTHOR]

Globally, more than half of potentially arable land is acidic, and aluminum (Al) is the primary factor limiting plant growth and crop productivity on acidic soils worldwide. The development and utilization of Al-tolerant crops is a sustainable approach to enhancing crop production on acidic soils. For this purpose, screening available genetic resources under Al-stressed conditions is a crucial initial step. Hence, the present study aimed to evaluate the Al tolerance of 264 Ethiopian chickpea landraces under hydroponic conditions without Al (control) and with 120 µM Al (Al treatment). Significant (p < 0.001) variations were detected among the genotypes for all studied traits under control (0 µM Al) and 120 µM Al concentration. The relative growth values for the 120 µM Al/0 µM Al ratio was also significant, indicating the presence of a considerable amount of genetic variation in Ethiopian chickpea landraces in terms of Al tolerance. Based on relative root growth (RRG) as an Al-tolerance parameter, the genotypes were grouped into five distinct (p < 0.001) classes. The highest RRG value (1.59) was obtained for genotype ETC_209008, followed by ETC_41184 and ETC_212589, while ETC_208995 had the lowest RRG value of 0.27. Of the total landraces screened, 35% had higher RRG values than the tolerant genotype ETC_WL_1_2016 used as a reference, indicating the presence of adequate genotypes capable of outperforming the reference genotype on acidic soils. The genotypes identified in the present study may serve as sources of novel alleles in genes regulating Al tolerance in chickpea that can be utilized in breeding programs to improve the crop's adaptation to acidic soils, thus contributing to smallholder farmers' increased nutritional and food security. [ABSTRACT FROM AUTHOR]

Aluminum (Al) toxicity is a major limiting factor for plant growth and crop production in acidic soils. This study aims to investigate the effects of γ-aminobutyric acid (GABA) priming on mitigating acid-Al toxicity to creeping bentgrass (Agrostis stolonifera) associated with changes in plant growth, photosynthetic parameters, antioxidant defense, key metabolites, and genes related to organic acids metabolism. Thirty-seven-old plants were primed with or without 0.5 mM GABA for three days and then subjected to acid-Al stress (5 mmol/L AlCl3·6H2O, pH 4.35) for fifteen days. The results showed that acid-Al stress significantly increased the accumulation of Al and also restricted aboveground and underground growths, photosynthesis, photochemical efficiency, and osmotic balance, which could be effectively alleviated by GABA priming. The application of GABA significantly activated antioxidant enzymes, including superoxide dismutase, peroxidase, catalase, and ascorbate peroxidase, to reduce oxidative damage to cells under acid-Al stress. Metabolomics analysis demonstrated that the GABA pretreatment significantly induced the accumulation of many metabolites such as quinic acid, pyruvic acid, shikimic acid, glycine, threonine, erythrose, glucose-6-phosphate, galactose, kestose, threitol, ribitol, glycerol, putrescine, galactinol, and myo-inositol associated with osmotic, antioxidant, and metabolic homeostases under acid-Al stress. In addition, the GABA priming significantly up-regulated genes related to the transportation of malic acid and citric acid in leaves in response to acid-Al stress. Current findings indicated GABA-induced tolerance to acid-Al stress in relation to scavenging of reactive oxygen species, osmotic adjustment, and accumulation and transport of organic metabolites in leaves. Exogenous GABA priming could improve the phytoremediation potential of perennial creeping bentgrass for the restoration of Al-contaminated soils. [ABSTRACT FROM AUTHOR]

Background and Aims: In acidic soils, aluminum (Al) toxicity remains a critical crop limitation that can be ameliorated by organic amendments through Al complexation with high-molecular-weight carbon compounds, particularly fulvic and humic acids (FA and HA) However, no research discriminates between the direct effects of FA and HA on plant growth and the indirect effect that occurs through ameliorating Al toxicity. This study delineates the direct and indirect effects of FA and HA on plant growth. Methods: Eucalyptus and Hay FA and HA, and Al effects on maize (Zea mays) root growth were investigated using dilute nutrient solution. Five Al concentrations (0–270 µM) were combined with four organic acid (OA) treatments, including Nil-OA, FA40, and HA40 (each at 40 mg C L−1) and a combined treatment FA40HA40 (80 mg C L−1). Results: Eucalyptus FA and HA stimulated root growth by ~20% compared with root growth in the Nil-OA (17.4 cm). In the absence of Al, Hay FA and HA inhibited root growth (by ~20%) compared with the Nil-OA but the addition of Al resulted in stimulation of root growth. In the presence of FA and HA, root growth was not inhibited by nominally toxic monomeric Al (Al3+) concentrations (~20 µM Al). However, when expressed on a relative basis to remove the direct effect of the ligand, the response was consistent with Al toxicity. Conclusions: The effects of FA and HA were either inhibitory or stimulatory depending on the source while both sources of FA and HA mitigated Al toxicity through complexation. The study provides mechanistic data that highlights limitations of soil bioassays where the direct effects of organic ligands on root growth are confounded with the indirect effect of their reduction of Al toxicity. These two independent processes must be considered in evaluating the amelioration of Al by organic amendments. [ABSTRACT FROM AUTHOR]

Over time, the use of plant-derived agents in the management of various human health conditions has gained a lot of attention. The study assessed the hepatoprotective potential of ethyl acetate fraction Tamarindus indica leaves (EFTI) during prenatal aluminum chloride exposure. Pregnant rats were divided into 5 groups (n = 4); Group I rats were administered 2 ml kg−1 of distilled water (negative control), Group II rats received only 200 mg kg−1 aluminum chloride (positive control), Group III rats were administered 200 mg kg−1 aluminum chloride and 400 mg kg−1 EFTI, Group IV rats were administered 200 mg kg−1 aluminum chloride and 800 mg kg−1 EFTI, Group V rats were administered 200 mg kg−1 aluminum chloride and 300 mg kg−1 Vit E (comparative control). On postnatal day 1, the pups were euthanized, and liver tissues were harvested for the biochemical study (tissue levels of malondialdehyde, caspase-3, tumor necrosis factor-alpha, aspartate aminotransferase, alkaline phosphatase, and alanine aminotransferases) and the liver histological examination. The administration of EFTI was marked with significant improvement in the tissue levels of malondialdehyde, caspase-3, tumor necrosis factor-alpha, aspartate aminotransferase, alkaline phosphatase, and alanine aminotransferases. There was a marked improvement in histopathological changes associated with prenatal aluminum chloride exposure. In conclusion, the administration of EFTI was protective during prenatal aluminum chloride exposure of the liver in Wistar rats, and is mediated by the anti-lipid peroxidative, antiapoptotic, and anti-inflammatory activity of EFTI.

AbstractAcute aluminum toxicity is encountered rarely in clinical practice but carries a high risk for morbidity and mortality. Despite this risk, our understanding of aluminum toxicity and its treatment is relatively limited. Due to decreased clearance, patients with renal failure have increased risk for significant aluminum-related central nervous system (CNS) toxicity. Medical advances have limited chronic aluminum exposure in these patients, but they are still at increased risk for acute toxicity from certain aluminum-based interventions such as alum bladder irrigation. We report a case of an 87-year-old man with end-stage renal disease on hemodialysis who developed acute aluminum toxicity from alum bladder irrigation. He was treated with daily deferoxamine infusions followed by dialysis with subsequent resolution of his encephalopathy. This case report uniquely documents trending of blood aluminum concentration (blood [Al]) during treatment providing insight into how aluminum blood concentrations shift during chelation therapy.

Aluminum is the most abundant metal element in the crust. Soil acidification will cause great increase of the aluminum solubility to produce a large number of Al3+, which is toxic to plants. The activated aluminum will inhibit root growth, affect nutrient absorption and many physiological and biochemical metabolism processes, and further reduce crop yield. Aluminum toxicity has been the most important limiting factor for crop growth in acid soils which account for about 40% of cultivated land in the world. Phytohormones are the key endogenous factors that regulate plant responses to various environmental stresses, and are crucial to the improvement of plant resistance and plant survival under various stresses. It is well known that abscisic acid, auxin, ethylene, cytokinin, jasmonic acid and other major plant hormones play an important role in regulating plant responses to aluminum toxicity stress. A large number of studies have shown that plant hormones can also improve the adaptability of plants to aluminum stress by regulating the activities of cell wall-modifying enzymes, reactive oxygen species metabolism and organic acid secretion. In addition, there are complex interactions between different plant hormone signals, which jointly mediate and regulate the adaptive response of plants to aluminum stress. In order to have a more comprehensive and in-depth understanding of the mechanism of plant hormones in aluminum toxicity response, and to provide new ideas for molecular genetic improvement of plants tolerance to aluminum toxicity, in the study, the signal transduction and regulation of plant hormone signals in the process of plant response to aluminum toxicity stress are reviewed, and the future research direction of plant hormones under aluminum toxicity stress is prospected.

The toxicity of aluminum (Al) in acidic soils poses a significant limitation to crop productivity. In this study, we found a notable increase in DnaJ (HSP40) expression in the roots of Al-tolerant alfalfa (WL-525HQ), which we named MsDjB4. Transient conversion assays of tobacco leaf epidermal cells showed that MsDjB4 was targeted to the membrane system including Endoplasmic Reticulum (ER), Golgi, and plasma membrane. We overexpressed (MsDjB4-OE) and suppressed (MsDjB4-RNAi) MsDjB4 in alfalfa hairy roots and found that MsDjB4-OE lines exhibited significantly better tolerance to Al stress compared to wild-type and RNAi hairy roots. Specifically, MsDjB4-OE lines had longer root length, more lateral roots, and lower Al content compared to wild-type and RNAi lines. Furthermore, MsDjB4-OE lines showed lower levels of lipid peroxidation and ROS, as well as higher activity of antioxidant enzymes SOD, CAT, and POD compared to wild-type and RNAi lines under Al stress. Moreover, MsDjB4-OE lines had higher soluble protein content compared to wild-type and RNAi lines after Al treatment. These findings provide evidence that MsDjB4 contributes to the improved tolerance of alfalfa to Al stress by facilitating protein synthesis and enhancing antioxidant capacity. [ABSTRACT FROM AUTHOR]

Acid soil syndrome leads to severe yield reductions in various crops worldwide. In addition to low pH and proton stress, this syndrome includes deficiencies of essential salt-based ions, enrichment of toxic metals such as manganese (Mn) and aluminum (Al), and consequent phosphorus (P) fixation. Plants have evolved mechanisms to cope with soil acidity. In particular, STOP1 (Sensitive to proton rhizotoxicity 1) and its homologs are master transcription factors that have been intensively studied in low pH and Al resistance. Recent studies have identified additional functions of STOP1 in coping with other acid soil barriers: STOP1 regulates plant growth under phosphate (Pi) or potassium (K) limitation, promotes nitrate (NO3-) uptake, confers anoxic tolerance during flooding, and inhibits drought tolerance, suggesting that STOP1 functions as a node for multiple signaling pathways. STOP1 is evolutionarily conserved in a wide range of plant species. This review summarizes the central role of STOP1 and STOP1-like proteins in regulating coexisting stresses in acid soils, outlines the advances in the regulation of STOP1, and highlights the potential of STOP1 and STOP1-like proteins to improve crop production on acid soils. [ABSTRACT FROM AUTHOR]

Main conclusion: The 4-coumarate:coenzyme A ligase 4CL4 is involved in enhancing rice P acquisition and use in acid soil by enlarging root growth and boosting functional rhizosphere microbe recruitment. Rice (Oryza sativa L.) cannot easily acquire phosphorus (P) from acid soil, where root growth is inhibited and soil P is fixed. The combination of roots and rhizosphere microbiota is critical for plant P acquisition and soil P mobilization, but the associated molecular mechanism in rice is unclear. 4CL4/RAL1 encodes a 4-coumarate:coenzyme A ligase related to lignin biosynthesis in rice, and its dysfunction results in a small rice root system. In this study, soil culture and hydroponic experiments were conducted to examine the role of RAL1 in regulating rice P acquisition, fertilizer P use, and rhizosphere microbes in acid soil. Disruption of RAL1 markedly decreased root growth. Mutant rice plants exhibited decreased shoot growth, shoot P accumulation, and fertilizer P use efficiency when grown in soil—but not under hydroponic conditions, where all P is soluble and available for plants. Mutant ral1 and wild-type rice rhizospheres had distinct bacterial and fungal community structures, and wild-type rice recruited some genotype-specific microbial taxa associated with P solubilization. Our results highlight the function of 4CL4/RAL1 in enhancing rice P acquisition and use in acid soil, namely by enlarging root growth and boosting functional rhizosphere microbe recruitment. These findings can inform breeding strategies to improve P use efficiency through host genetic manipulation of root growth and rhizosphere microbiota. [ABSTRACT FROM AUTHOR]

Background and Aims: Suitable N source supply is critical to improve plant growth and N uptake, but the importance of nitrate (NO3−) for rice (Oryza sativa L.) and microbiota is often neglected in acidic paddy soils where ammonium (NH4+) is dominant. This study aimed to explore the differential effects of NH4+ and NO3− on rice growth, fertilizer nitrogen recovery efficiency (FNRE), and rhizosphere bacterial community in acid soil. Methods: Two rice varieties, Kasalath (Al-sensitive indica) and Koshihikari (Al-tolerant japonica), were exposed to different N sources with or without lime in an acid soil. Results: Liming and NO3− application solely improved the growth and FNRE of the Al-sensitive rice, namely, by increasing soil pH and alleviating Al toxicity. Compared with liming and rice variety, N source had a more pronounced influence on rhizobacterial community composition. Of the two sources, NO3− had a stronger effect on the rhizobacterial community than NH4+. Remarkably, rice plants fed with NH4+ specifically recruited Desulfosporosinus and Desulfitobacterium associated with ferric NH4+ oxidation in the rhizosphere, whereas those exposed to NO3− recruited Alicyclobacillus with NO3−-reducing iron oxidation ability. Three keystone taxa were identified in a rhizobacterial co-occurrence network analysis: Alicyclobacillus, which was positively associated with rice growth and FNRE, and Acidobacteriales and WPS-2, both with negative associations. Conclusion: Compared with NH4+, NO3− enhances the growth and FNRE of Al-sensitive rice and exerts dominant effects on the rhizobacterial community, which indicates the importance of NO3− for rice and has instructive implications for N management in acid soil. [ABSTRACT FROM AUTHOR]

Aluminum (Al) toxicity and phosphorus (P) deficiency are widely recognized as major constraints to agricultural productivity in acidic soils. Under this scenario, the development of ryegrass plants with enhanced P use efficiency and Al resistance is a promising approach by which to maintain pasture production. In this study, we assessed the contribution of growth traits, P efficiency, organic acid anion (OA) exudation, and the expression of Al-responsive genes in improving tolerance to concurrent low-P and Al stress in ryegrass (Lolium perenne L.). Ryegrass plants were hydroponically grown under optimal (0.1 mM) or low-P (0.01 mM) conditions for 21 days, and further supplied with Al (0 and 0.2 mM) for 3 h, 24 h and 7 days. Accordingly, higher Al accumulation in the roots and lower Al translocation to the shoots were found in ryegrass exposed to both stresses. Aluminum toxicity and P limitation did not change the OA exudation pattern exhibited by roots. However, an improvement in the root growth traits and P accumulation was found, suggesting an enhancement in Al tolerance and P efficiency under combined Al and low-P stress. Al-responsive genes were highly upregulated by Al stress and P limitation, and also closely related to P utilization efficiency. Overall, our results provide evidence of the specific strategies used by ryegrass to co-adapt to multiple stresses in acid soils.