Integrated application of organic acids and earthworms improves rhizosphere microbiome, reduces health risks, and modulates proteomic and transcriptomic responses in rice (Oryza sativa L.) under aluminum stress.

Soil contamination with toxic heavy metals [such as aluminum (Al)] is becoming a serious global problem due to the rapid development of the social economy. Although plant growth-promoting rhizo-bacteria (PGPR) are the major protectants to alleviate metal toxicity, the study of these bacteria to ameliorate the toxic effects of Al is limited. Therefore, the present study was conducted to investigate the combined effects of different levels of Acinetobacter calcoaceticus (5ppm and 10ppm) of accession number of MT123456 on plant growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress and response of antioxidant compounds (enzymatic and nonenzymatic), and their specific gene expression, sugars, nutritional status of the plant, organic acid exudation pattern and Al accumulation from the different parts of the plants, which was spiked with different levels of Al [0µM (i.e., no Al), 50µM, and 100µM] using aluminum sulfate [Al2(SO4)3] in wheat (Triticum aestivum L.). Results from the present study revealed that the Al toxicity induced a substantial decreased in shoot length, root length, number of leaves, leaf area, shoot fresh weight, root fresh weight, shoot dry weight, root dry weight, chlorophyll-a, chlorophyll-b, total chlorophyll, carotenoid content, net photosynthesis, stomatal conductance, transpiration rate, soluble sugar, reducing sugar, non-reducing sugar contents, calcium (Ca2+), magnesium (Mg2+), iron (Fe2+), and phosphorus (P) contents in the roots and shoots of the plants. In contrast, increasing levels of Al in the soil signifcantly (P < 0.05) increased Al concentration in the roots and shoots of the plants, phenolic content, malondialdehyde (MDA), hydrogen peroxide (H2O2), electrolyte leakage (EL), fumaric acid, acetic acid, citric acid, formic acid, malic acid, oxalic acid contents in the roots of the plants. Although, the activities of enzymatic antioxidants such as superoxidase dismutase, peroxidase, catalase, ascorbate peroxidase and their specific gene expression in the roots and shoots of the plants and non-enzymatic such as phenolic, favonoid, ascorbic acid, and anthocyanin contents were initially increased with the exposure of 50µM Al, but decreased by the increasing the Al concentration 100µM in the soil. Addition of A. calcoaceticus into the soil signifcantly alleviated Al toxicity effects on T. aestivum by improving photosynthetic capacity and ultimately plant growth. Increased activities of antioxidant enzymes in A. calcoaceticus-treated plants seem to play a role in capturing stress-induced reactive oxygen species as was evident from lower levels of MDA, H2O2, MDA, and EL in A. calcoaceticus-treated plants. Research findings, therefore, suggested that A. calcoaceticus application can ameliorate Al toxicity in T. aestivum seedlings and resulted in improved plant growth and composition under metal stress as depicted by balanced exudation of organic acids.

Soil contamination with microplastics (MPs) is a persistent threat to crop production worldwide. With a wide range of MP types, including polystyrene (PS), polyvinyl chloride (PVC) and polyethylene (PE), contaminating our environment, it is important to understand their impact on agricultural productivity. The present study was conducted to investigate the effects of different types of MPs (PS, PVC and PE) on various aspects of plant growth. Specifically, we examined growth and biomass, photosynthetic pigments, gas exchange attributes, oxidative stress responses, antioxidant compound activity (both enzymatic and non-enzymatic), gene expression, proline metabolism, the AsA-GSH cycle and cellular fractionation and nutritional status, in different parts of rice (Oryza sativa L.) seedlings, which were also exposed to plant growth promoting rhizobacteria (PGPR), i.e. Bacillus mycoides PM35, i.e. 20 μL. The research outcomes indicated that the different types of MPs in the soil notably reduced plant growth and biomass, photosynthetic pigments and gas exchange attributes. However, MP stress also induced oxidative stress in the roots and shoots of the plants by increasing malondialdehyde (MDA), hydrogen peroxide (H2O2) and electrolyte leakage (EL) which also induced increased compounds of various enzymatic and non-enzymatic antioxidants and also the gene expression. Furthermore, a significant increase in proline metabolism, the AsA-GSH cycle, and the fractionations of cellular components was observed. Although the application of B. mycoides PM35 showed a significant increase in plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased oxidative stress. In addition, the application of B. mycoides PM35 enhanced cellular fractionation and decreased the proline metabolism and AsA-GSH cycle in O. sativa plants. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of MP contamination in agricultural soils.

Using common beans differing greatly in the response to photoperiod and low-phosphorus (P) stress, we investigated their responses to acidity and aluminum (Al) toxicity and the relationship between Al tolerance and organic acid exudation under Al or low P stress. A genotype Ginshi was found to be sensitive to low pH treatment. When exposed to pH 4.5, serious curvature in the root tips of cv. Ginshi was observed; however, it was completely corrected by the application of 5 or 10 μmol/L AlCl3; increasing calcium (Ca) could ameliorate Al toxicity, but it could not correct root curvature at pH 4.5. Common beans showed significant differences in both root growth and Al tolerance, and the varieties from the Andes were more tolerant to Al toxicity than those from the Mesoamerican origin. In the presence of 50 μmol/L AlCl3, all the common bean genotypes exuded citrate, and a significant difference in the amounts of citrate was observed among genotypes. The genotypes originated in the Mesoamerica tended to release more citrate than other origins in the presence of Al. The P-inefficient genotype DOR364 exuded more citrate than the P-efficient genotype G19833 in the presence of 50 μmol/L AlCl3, whereas no organic acids were detected in root exudates under low-P stress. A reduction of citrate exudation in the DOR364, but a slight increase of citrate exudation in the G19833, was observed under Al stress after they were exposed to 6-d P starvation. These results suggest that different low-P or Al tolerance in common beans might not be associated with organic acid exudation.

Mitigating chromium toxicity in rice (Oryza sativa L.) via ABA and 6-BAP: Unveiling synergistic benefits on morphophysiological traits and ASA-GSH cycle

Soil contamination with salinity and heavy metals such as cadmium (Cd) is becoming a serious global problem due to the rapid development of the social economy. Although plant growth-promoting rhizobacteria PGPR and organic agents such as salicylic acid (SA) are considered major protectants to alleviate abiotic stresses, the study of these bacteria and organic acids to ameliorate the toxic effects of salinity and Cd remains limited. Therefore, the present study was conducted to investigate the individual and combined effects of PGPR and SA on enhancing the phytoremediation of salinity (100 mM NaCl) and Cd (50 µM CdCl₂) using rice (Oryza sativa L.) plants. The research results indicated that elevated levels of salinity and Cd stress in soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, and gas exchange attributes. However, salinity and Cd stress also induced oxidative stress in the plants by increasing malondialdehyde (MDA) and hydrogen peroxide (H2O2) by 44% and 38%, respectively, which also induced increased compounds of various enzymatic and nonenzymatic antioxidants, and also the gene expression and sugar content. Furthermore, a significant (P < 0.05) increase in cadmium accumulation, potential health risk indices, proline metabolism, the AsA–GSH cycle, and the pigmentation of cellular components was observed. Although the application of PGPR and SA showed a significant (P < 0.05) increase in plant growth and biomass, gas exchange characteristics, microbial diversity, functional gene abundance in the rhizosphere, enzymatic and nonenzymatic compounds, and their gene expression, and also decreased oxidative stress. In addition, the application of PGPR and SA enhanced cellular fractionation and decreased metal accumulation by 37% in shoots, proline metabolism, and the AsA–GSH cycle in O. sativa plants. These results provide new insights for sustainable agricultural practices and hold immense promise in addressing the pressing challenges of salinity and heavy metal contamination in agricultural soils.

Although the studies on nitric oxide (NO) in Al toxicity has been reported, the results are controversial. The aim of this study is to investigate the role of NO in Al-induced root growth inhibition in soybean (Glycine max L.). NO donor and scavenger were used to test the effects of NO on root elongation, lipid peroxidation, reactive oxygen species (ROS) accumulation, and ascorbate-glutathione cycle (AsA-GSH) under Al stress. Application of butylated hydroxyanisole, a lipophilic antioxidant, reduced Al-induced lipid peroxidation and root inhibition. NO donor alleviated Al-induced root inhibition and ROS accumulation as well as lipid peroxidation, while NO scavenger aggravated the observed effects of Al. In addition, NO accumulation in root apexes under Al stress was mediated by nitrate reductase (NR). Furthermore, the levels of GSH and AsA were enhanced by Al and further elevated by NO donor, but suppressed by NO scavenger. Moreover, the activities of key enzymes in AsA-GSH cycle were positively regulated by NO under Al stress. These results indicate that NR-mediated NO improves Al-induced root growth inhibition, possibly through its regulation of AsA-GSH cycle to maintain high levels of AsA and GSH, subsequently reducing ROS accumulation and thus alleviating lipid peroxidation.

RETRACTED: Proteomic modulation by arsenic and microplastic toxicity in the presence of iron oxide nanoparticles in wheat (Triticum aestivum L.) seedlings

Mitigating cadmium stress in rice (Oryza sativa L.) using succinic and oxalic acids with focus on cellular integrity and antioxidant responses.

Aluminum (Al) toxicity represents a significant constraint on crop growth in acidic soils. Al stress can stimulate the biosynthesis of melatonin (MT) in rice (Oryza sativa L.). The exogenous application of 20 μM MT markedly reduces Al accumulation in root tips and effectively mitigates Al stress. By enhancing the levels of root hemicellulose and down-regulating the expression of two genes sensitive to aluminum rhizotoxicity (OsSTAR1 and OsSTAR2), which function to obscure Al binding sites within the cell wall, MT significantly improves the fixation of Al by the cell wall. Furthermore, MT diminishes cytoplasmic entry of Al by reducing expression levels of nramp aluminum transporter 1 gene (OsNRAT1), while inducing expression of an aluminum-sensitive gene (OsALS1), thereby promoting vacuolar compartmentation to lower cytoplasmic Al concentration. Additionally, MT substantially decreases Nitric oxide (NO) accumulation induced by Al in roots. The alleviation effect exerted by MT on Al toxicity can be replicated through administration of the NO scavenger carboxyl-PTIO (c-PTIO). Moreover, the Al-sensitive phenotype exhibited in the osgsnor mutant, coupled with the absence of mitigation by MT, further substantiates that MT alleviates Al toxicity in rice primarily via regulation of NO content, potentially relying on NO signal transduction pathways. In summary, MT plays a pivotal role in modulating rice resistance to Al toxicity and stimulates multiple pathways to enhance tolerance against this abiotic stressor. This study provides new insights into understanding mechanisms underlying rice resistance to abiotic stresses.

Nanoscale particles-induced mitigation of tannery wastewater chromium stress in rice: Implications for plant performance and human health risk assessment.

Utilizing phytohormones-brassinosteroids (BRs), jasmonic acid (JA), and strigolactones (SLs) presents a novel approach to overcome toxicity of arsenic (As) in agricultural settings. The present study investigates the role of three phytohormones BRs, JA, and SLs in ameliorating As-induced stressed in Oryza sativa L. (rice) seedlings. s In the present study, we have used different levels of BRs (0.1 µM), JA (1 µM), and SLs (0.05 µM) every 7 days to O. sativa seedlings when exposed to different levels of As levels of 100 mg-1 kg and 200mg kg-1 (as sodium arsenate) to examine various growth and biochemical parameters in O. sativa. The results showed that the As toxicity in the soil showed a significantly (P < 0.05) declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in O. sativa. However, As toxicity significantly (P < 0.05) increased oxidative stress biomarkers, enzymatic and nonenzymatic antioxidants including their gene expression in O. sativa. Although, the application of phytohormones including BRs, JA, and SLs showed a significant (P < 0.05) increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, and As uptake. In addition, individual or combined application of phytohormones including BRs, JA, and SLs enhanced the cellular fractionation and decreases the proline metabolism and AsA - GSH cycle in O. sativa. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Assemblage of root-associated microbiome contributes to disparate performance of two rice genotypes under aluminum stress.

Seedlings growing in acid soils suffer both phosphorus (P) deficiency and aluminium (Al) toxicity stresses. An experiment was conducted to study the effects of Al and P interaction on Al-tolerant (ET8) and Al-sensitive (ES8) wheat genotypes in an acid soil. This study aimed to determine the interactive effect of Al and P in soil and within plant tissue. Three Al levels (0, 50 and 150 mg aluminium chloride [AlCl3] kg−1 soil) and five P levels (0, 20, 40, 80 and 160 mg P kg−1) were used in this experiment. Bulk soil pH decreased with addition of AlCl3 to the soil. Bulk soil pH increased at 160 mg P kg−1 supply at three Al levels. Phosphorus supply reduced extractable Al in the soil in all Al treatments. Seedlings suffered more from Al toxicity in the absence of P supply. Increasing P supply resulted in increased seedling biomass under high Al toxicity. This high P ameliorated Al toxicity in the soil and may enhance ES8 growth under Al toxicity. The Al × P interaction affected the root and shoot P concentration in both genotypes and P supply had no effect on P translocation to the shoot. These results suggested that differential growth behaviour between ES8 and ET8 plays an important role in tolerance to Al toxicity irrespective of high P supply. It is concluded that the higher aluminium cation (Al3+) binding capacity in the root apoplast of ET8 seedlings contributes to its improved tolerance to Al toxicity compared to ES8 seedlings.

Aluminum (Al) toxicity is a major agronomic problem in acid soils. Most studies regarding Al stress focus on phenomena occurring in the roots; however, less is known about the effects of Al stress on photosynthetic apparatus functionality. Our aim was to rank three highbush blueberry (Vaccinium corymbosum) cultivars according to their tolerance to acid and Al stresses. Additionally, the levels of Al toxicity for highbush blueberry were established. ‘Brigitta’, ‘Legacy’, and ‘Bluegold’ were grown in a greenhouse in hydroponic solutions containing different Al concentrations (0, 25, 50, 75, and 100 μm) for 0 to 48 h and were allowed to recover (without Al) over 24 h. In all Al-treated cultivars, root growth inhibition was found at the highest Al treatment. However, ‘Brigitta’ also showed root growth up to 75 μm Al. Photochemical parameters decreased substantially due to Al treatments in ‘Bluegold’ (up to 98% inhibition) and ‘Legacy’ (up to 80% inhibition) without total recovery. In contrast, ‘Brigitta’ showed a better photosystem II performance and root growth than the other cultivars. These results suggest that ‘Brigitta’ is the best cultivar for use in acid soils with Al toxicity, followed by ‘Legacy’. ‘Bluegold’ was highly sensitive to Al stress. In addition, Al toxicity levels for blueberries depend on the genotype studied.

The growth of mungbean (Vigna radiata (L.) Wilczek) seedlings and cuttings (without roots) was studied in a growth chamber, to determine the effect of boron (B) on aluminium (Al) toxicity for plant growth by adding two concentrations of B (5, 50 µM)under Al stress. We found that B at 50 µM in the nutrient solutions at 2 or 5 mM Al, increased the height of intact seedlings, and the fresh and dry weights of the seedlings compared to that at 5 µM. It also promoted the elongation of the epicotyl and hypocotyl of intact seedlings under Al stress. Boron at 50 µM increased the content of chlorophyll in the seedlings which suffered from Al toxicity. However, since B had no amelioration effect for the cuttings under Al stress it appears that B alleviation of Al toxicity was related to the roots. The possible relationship between the effects of B and Al toxicity is discussed.