Synergistic effect of naphthalene acetic acid and salicylic acid on the growth and tolerance mechanism of cucumber under salt stress

Abstract

High soil salinity significantly hampers plant growth and crop yield by disrupting metabolic functions and causing oxidative, osmotic, and ionic stress. This study investigated the combined effects of naphthalene acetic acid (NAA) and salicylic acid (SA) in reducing salt stress in cucumber (Cucumis sativus L.) cv. AR-8, filling a knowledge gap regarding multilateral plant growth regulator (PGR) interactions under saline conditions. Cucumber seedlings were subjected to 80 mM NaCl, with or without 200 ppm NAA and 300 ppm SA. Salt stress notably decreased seedling vigor, biomass, and chlorophyll levels. However, combined NAA and SA treatments significantly mitigated these effects, leading to improvements in leaf area, plant height, and root activity compared to untreated stressed plants. The PGRs also enhanced fruit quality by increasing vitamin C, soluble sugars, and protein content. Additionally, they reduced oxidative stress markers such as electrolyte leakage and lipid peroxidation, while boosting antioxidant enzyme activities like catalase, ascorbate peroxidase, superoxide dismutase, and peroxidase. The treatments further influenced carbohydrate and nitrogen metabolism by modulating key enzymes, including sucrose phosphate synthase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase. This research highlights the synergistic effect of NAA and SA in promoting cucumber tolerance to salt stress and offers new insights into using multiple PGRs for crop resilience in saline environments. Future studies should aim to optimize PGR combinations and explore their molecular mechanisms in different crops under various stress conditions.