Exogenous application of proline alleviates salt-induced oxidative stress in Phaseolus vulgaris L. plants

Abstract

SummaryTwo field experiments on common bean (Phaseolus vulgaris L.) plants were conducted at three sites having different levels of salinity (EC = 1.84, 6.03, or 8.97 dS m–1) and considered to be low, moderate, or highly saline soil, respectively. The aim was to examine the effects of three successive exogenous applications of 5.0 mM proline, applied as foliar sprays at 20, 30, and 40 d after sowing (DAS) to each plant at each site. Bean plants were sampled 50 DAS and the effects of the proline sprays on various growth parameters, levels of photosynthetic pigments, endogenous proline, ascorbic acid, nitrate, nitrite, and mineral nutrient (P, K, Na) concentrations, and anti-oxidant enzyme activities were measured in order to understand the mechanism(s) of salt tolerance in proline-treated bean plants. Exogenous applications of 5 mM proline alleviated oxidative stress and enhanced the growth of all treated common bean plants. Proline also increased the activities of the anti-oxidant enzymes, superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), as well as the concentrations of carotenoids, ascorbic acid, and endogenous proline. Spray applications of proline increased the concentrations of P and K+, and decreased Na+ ion concentrations, in salt-affected plants. Thus, the K+:Na+ ratio increased. Based on these findings, we recommend the use of proline as a commercial formulation to enhance plant growth and production in common bean plants grown under saline conditions.