Tyrosine or lysine priming modulated phenolic metabolism and improved cadmium stress tolerance in mung bean (Vigna radiata L.)

Cadmium stress deleteriously affects plant growth and yield with disturbed plant metabolism. Phenylpropanoid pathway (PePP) is an important component of plant secondary metabolism known to produce nutraceutical antioxidants. We hypothesized that tyrosine (Tyr) and lysine (Lys) vary in their metabolic entry into PePP pathway and modulate it differently. Hence, a completely randomized experiment was planned with four replicates; 12 hours primed (control, hydroprimed, 0.2% Tyr, and 0.2% lysine) mungbean seeds with two stress levels (0 and 0.22 mM CdCl2). Harvests were planned at vegetative and fully mature stages of growth. Attributes like total soluble proteins, total phenolic contents, flavonoids, membrane damage characteristics, and phenolic profile were used to compare the efficacy of applications. Cadmium (0.22 mM) reduced growth in terms of leaf dry weight, leaf area, germination percentage, root vigor, shoot vigor, number of pods, and soluble proteins. Enhanced levels of malondialdehyde (MDA) and relative Root Electrolyte Leakage indicated oxidative damage in stressed plants. Other parameters of growth and yield remained ineffective with increased accumulation of phenolics and flavonoids indicative of moderate cadmium tolerance. Lys and Tyr priming improved root fresh weight, shoot length, leaf dry weight, germination percentage, root and shoot vigor, number of pods, soluble proteins, phenolics and flavonoids with reduction of MDA and root electrolyte leakage. Activity of PAL, leaf number and leaf area were exclusively increased in Tyr primed stressed plants. Tyr directly and Lys indirectly affected products of PePP with improved stress tolerance in mung bean.