Poly-glutamic acid reinforces wheat cadmium tolerance by modulating ascorbic acid and glutathione metabolism

We investigated the influence of poly-glutamic acid (PGA) on ascorbic acid (AsA) and glutathione (GSH) metabolism in leaves of wheat seedlings under cadmium (Cd) stress. The results showed that Cd stress enhanced ascorbate peroxidase, dehydroascorbate reductase, monodehydroascorbate reductase, glutathione reductase, gamma-glutamylcysteine synthetase and L-galactono-1,4-lactone dehydrogenase activities, and increased AsA and GSH contents. Whereas Cd reduced AsA/dehydroascorbic acid (DHA) and GSH/oxidised glutathione (GSSG) ratios and increased malondialdehyde (MDA) content and electrolyte leakage (EL). Meanwhile, Cd stress improved Cd accumulation and nonphotochemical quenching (qN) and decreased soil and plant analyser development (SPAD) value, net photosynthetic rate (Pn), maximum photochemical efficiency of PSII (Fv/Fm), photochemical quenching (qP), quantum efficiency of PSII photochemistry (ΦPSII), wheat height and dry biomass. Compared to Cd alone, PGA plus Cd stress reinforced AsA and GSH metabolism via the above enzymes and increased AsA and GSH contents and their redox status. PGA plus Cd stress also decreased MDA content and EL. Besides, PGA plus Cd stress decreased Cd accumulation and increased SPAD value, Pn, qN, Fv/Fm, qP, ΦPSII, wheat height and dry biomass. Moreover, PGA alone showed positive effects on the indicators mentioned above. Our results clearly indicated that PGA enhanced wheat Cd tolerance by preventing Cd uptake and enhancing AsA and GSH metabolism. Therefore, PGA can be applied to enhance wheat Cd tolerance in production.