Ameliorative effects of seed treated with phytohormones on seedling growth, soluble protein content and antioxidant enzymes of hargel (Solenostemma argel Hayne) seedlings under salt stress

Abstract

Salinity stress profoundly affects crop plants’ morphological structures and physiological processes, decreasing plant growth and development. The application of phytohormones has been proved an efficient way to alleviate salinity stress. This study was done to evaluate the effects of exogenous application of gibberellic acid (GA3; 0.288 mM), salicylic acid (SA; 0.362 mM), indole acetic acid (IAA; 0.285 mM) and control (0 mM) on seedling growth and physiological parameters of hargel (Solenostemma argel Hayne) seedlings under different salinity levels (0, 50 and 100 mM NaCl). Significant decreases due to salinity stress were observed in all the seedling growth parameters shoot and root length, shoot fresh weight, shoot dry weight, root fresh weight, root dry weight, chlorophyll a and b content, and antioxidant enzymes activities such as superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX). In contrast, soluble protein and carotenoid content increased with increasing salinity. At high salinity level, GA3 increased carotenoid content and APX activity by 56.4% and 53.4%, respectively, while SA increased shoot dry weight, SOD, POD and soluble protein by 1.3-fold, 1.3-fold, 1.95-fold and 93.2%, compared with the control, IAA increased root length and fresh root weight at the same salinity level by 1.58-fold and 2-fold, respectively. In conclusion, seed priming with an appropriate dosage of exogenous hormones successfully mitigates the adverse effects of NaCl by increasing photosynthetic pigment, antioxidant enzyme activity and seedling growth parameters. Furthermore, SA exhibited the best mitigating effects compared to IAA and GA3.