Evaluating the potential of Acinetobacter calcoaceticus in alleviation of aluminium stress in Triticum aestivum.

Abstract

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 (5 ppm and 10 ppm) 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 [0 µM (i.e., no Al), 50 µM, and 100 µM] 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 50 µM Al, but decreased by the increasing the Al concentration 100 µM 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.