Endophyte infection enhances accumulation of organic acids and minerals in rice under Pb2+ stress conditions

This study aimed to assess the effects of endophyte infection on Pb accumulation, organic acids (OAs) and mineral element contents by comparing endophyte-uninfected (E-) and endophyte-infected (E+) rice exposed to 0, 10.36, 20.72, 31.08 and 41.44 mg/L Pb2+ for 10 days. Pb2+ stress decreased growth, dry weight, and chlorophyll (Chl) content in E- and E+ in a concentration-dependent manner. Pb2+ accumulation was similar in E- and E+. Under Pb2+ stress, E+ accumulated more malate and fumarate in the leaves compared to E-, as well as more tartrate, malate, succinate and fumarate in the roots. Furthermore, E+ secreted more malate and lactate under 41.44 mg/L Pb2+ stress. Malate accumulation was induced by endophyte infection under Pb2+ exposure suggesting that malate is the most obvious candidate ligand for Pb2+. Endophyte infection increased Ca, Mg, P, Fe and Ni contents in the leaves and Ni contents in the roots under Pb2+ stress, but reduced Fe content in the roots under high Pb2+ stress. Under same Pb2+ concentration, endophyte infection significantly increased plant height, the dry weight of the shoots, and Chl content. The effects of endophyte infection might be due to changes in OAs accumulation and exudation and improvements in mineral uptake under Pb2+ stress.