Variations in Sweet Pepper Growth, Physiology, and Gene Expression in Shock and Gradual Salt Stress

Abstract

ABSTRACT Salinity is a major abiotic stressor that can significantly impact plant growth and productivity. To evaluate the physiological responses of sweet pepper (Capsicum annuum L. Ps301) to gradual salinity stress (SLS) and shock salinity stress (STS), an experiment was conducted using a factorially based completely randomized design (CRD). The sodium chloride (NaCl) induced salinity treatments were administered in the nutrient solution in two forms: STS and SLS. The SLS was applied for 8 days, with stress levels increasing every 2 days; STS was administered for 48 h. The signaling response was activated more rapidly and abruptly in response to STS; however, after the various adaptive responses to salinity, these signals were more activated in response to SLS. The STS led to plant growth a greater decrease than SLS. The electrolyte leakage (EL) increased under both SLS and STS by 60% and 61% compared to the control, respectively. Other stress indices, such as phenol and abscisic acid (ABA) content, increased by 26% and 71% under SLS compared to STS. Salinity increased the leaf water potential (LWP) in two salt regimes, and the root water potential (RWP) in STS conditions only. Salinity stress decreased plasma membrane intrinsic protein gene expression in roots, especially in STS compared to SLS. The STS increased plasma membrane intrinsic protein (PIP) expression in leaves more than SLS. It was concluded that salinity impairs the growth and physiological characteristics of pepper; however, the signaling and stress indices respond differently to STS and SLS application.