L-glutamic Acid and L-aspartic Acid Supplementation Mitigate Heavy Metal-Induced Stress in Phaseolus vulgaris L.

Heavy metal contamination in the environment, resulting from human activities or natural processes, poses a significant and widespread challenge. L-glutamic (L-glu) and L-aspartic acid (L-asp) treatments have been reported to improve plant metabolism of heavy metal-exposed plants, but the role of these amino acids in the resistance to lead (Pb2+), cadmium (Cd2+), arsenic (As3+) and nickel (Ni2+) treated-bean are unclear when applied together. This study investigated the L-glu and L-asp supplementation-induced changes in some physio-biochemical parameters and some stress-related gene expression levels in Pb2+, Cd2+, As3+, and Ni2+-stressed Phaseolus vulgaris (Elkoca and Gina) grown in nutrient solution. The combination of two L-glu and L-asp (1.5 and 3 mM) and Cd2+ (1 mM), Pb2+ (1 mM), As3+ (2 mg/L-1), and Ni2+ (1 mM) concentrations were used. The physio-biochemical parameters of the leaves were determined based on the chlorophyll content (SPAD), relative water content (RWC), hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte conductivity (EC) contents, and the metal tolerance protein (MTP) genes, known for their role in heavy metal detoxification, and as PvSOD, PvPOD, and PvAPX antioxidant enzyme genes were analyzed for their temporal expression patterns in leaves. Preliminary results indicate a nuanced response of PvMTPs genes, highlighting potential variations in genotype-specific expression. Among the analyzed PvMTP7, PvMTP8, PvMTP9, PvMTP10, PvMTP11, and PvMTP13 genes, PvMTP10 exhibited particularly higher expression values in all treatments. In heavy metal-exposed beans, there was a concurrent decrease in SPAD, RWC, H2O2, and MDA contents, coupled with an increase in EC values. In turn, L-glu and L-asp pretreatments decreased the harmful effects of heavy metals by increasing the SPAD and RWC values and decreasing the EC, H2O2, and MDA contents and they reached these values close to control. Also, they improved the expressions of the above-mentioned genes. The 3 mM L-glu and L-asp appear to be more effective than 1.5 mM L-glu and L-asp in alleviation of the heavy metal's toxic effects on two genotypes of bean. The findings contribute to our understanding of some stress-related gene expression levels and physio-biochemical responses under heavy metal stresses and offer insights into the potential application of L-glu and L-asp in enhancing stress tolerance in plants.