Modulation of Glycine Betaine Accumulation with Oxidative Stress Induced by Aluminium Toxicity in Rice

Aluminum in plant: Benefits, toxicity and tolerance mechanisms

Aluminum (Al) is the third most ubiquitous metal in the earth's crust. A decrease in soil pH below 5 increases its solubility and availability. However, its impact on plants depends largely on concentration, exposure time, plant species, developmental age, and growing conditions. Although Al can be beneficial to plants by stimulating growth and mitigating biotic and abiotic stresses, it remains unknown how Al mediates these effects since its biological significance in cellular systems is still unidentified. Al is considered a major limiting factor restricting plant growth and productivity in acidic soils. It instigates a series of phytotoxic symptoms in several Al-sensitive crops with inhibition of root growth and restriction of water and nutrient uptake as the obvious symptoms. This review explores advances in Al benefits, toxicity and tolerance mechanisms employed by plants on acidic soils. These insights will provide directions and future prospects for potential crop improvement.

Enhanced exudation of malate in the rhizosphere due to AtALMT1 overexpression in blackgram (Vigna mungo L.) confers increased aluminium tolerance

Worldwide, 50% of soil is acidic, which induces aluminium (Al) toxicity in plants, as the phyto-availability of Al³⁺ increases in acidic soil. Plants responds to Al³⁺ toxicity by exuding organic acids into the rhizosphere. The organic acid responsible for Al³⁺ stress response varies from species to species, which in the case of blackgram (Vigna mungo L.) is citrate. In blackgram, an Arabidopsis malate transporter, AtALMT1, was overexpressed with the motive of inducing enhanced exudation of malate. Transgenics were generated using cotyledon node explants through Agrobacterium tumefaciens-mediated transformation. The putative transgenics were initially screened by AtALMT1-specific genomic DNA PCR, followed by quantitative PCR. Two independent transgenic events were identified and functionally characterized in the T₃ generation. The transgenic lines, Line 1 and 2, showed better root growth, relative water content and chlorophyll content under Al³⁺ stress. Both lines also accounted for less oxidative damage, due to reduced accumulation of ROS molecules. Photosynthetic efficiency, as measured in terms of F_v /F_m , NPQ and Y(II), increased when compared to the wild type (WT). Relative expression of genes (VmSTOP1, VmALS3, VmMATE) responsible for Al³⁺ stress response in blackgram showed that overexpression of a malate transporter did not have any effect on their expression. Malate exudation increased whereas citrate exudation did not show any divergence from the WT. A pot stress assay found that the transgenics showed better adaptation to acidic soil. This report demonstrates that the overexpression of a malate transporter in a non-malate exuding species improves adaptation to Al³⁺ toxicity in acidic soil without effecting its stress response mechanism.