Pumpkin seed protein hydrolysate treatment alleviates salt stress effects on Phaseolus vulgaris by elevating antioxidant capacity and recovering ion homeostasis

Pumpkin seed protein hydrolysate (PH) is a biostimulant product that contains high antioxidant activities, peptides and amino acids. This biostimulant is able to improve plant tolerance to abiotic stresses, including salinity. A pot experiment was conducted during summer season of 2018, with the aim o f determining growth and productivity, physio-biochemical attributes, and antioxidant system components in salt (3.9 or 7.8 dS m(-1) using NaCl)-stressed Phaseolus vulgaris plants treated with PH (1000 or 2000 mu L L-1). Salt stress was applied in irrigation water, and PH was applied three times as foliar application. Under 7.8 dS m(-1), Na+ content was significantly increased, however, PH application at 1000 or 2000 mu L L-1 reduced it by 11 or 13%, respectively. The negative impacts of salinity on essential nutrients (e.g., N, P, K+ , Ca2+, and Mg2+) contents, leaf photosynthetic pigments contents, and tissue health (in terms of relative water content, membrane stability index, and excised leaf water retention) were considerably mitigated by PH application. Increase in malondialdehyde (MDA) content was associated by increases in proline, soluble sugars, and glutathione contents, and antioxidant enzyme activities under salt stress, however, PH application further improved these parameters along with a worthy reduction in MDA content in salt-stressed plants. PH can maintain plant anatomical features, growth and yield measurements, which were disrupted by salt stress. Results o f this study recommend the use o f PH as foliar application, especially at 2000 mu L L-1 to obtain satisfactory growth and yield of Phaseolus vulgaris plants grown under salt stress up to 7.8 dS m(- 1).