Exogenous menadione sodium bisulfite mitigates specific ion toxicity and oxidative damage in salinity-stressed okra (Abelmoschus esculentus Moench)

Abstract

Salinity, being a major environmental constraint, impedes plant growth and productivity worldwide. Menadione sodium bisulfite (MSB) was previously studied as activator of plant defense responses against pathogens. We further studied the potential of MSB in salt tolerance. MSB compound derived from vitamin K is soluble in water and possesses the potential to mediate plant defense responses to abiotic stress such as salinity. In the present experiment, foliar application of MSB (0, 50, 100, 150 and 200 µM) markedly mitigated salinity (100 mM) effects on two okra cultivars (Shabnam-786 and Arka Anamika). Salinity stress significantly decreased growth, chlorophyll and K+ content, but increased the tissue contents of Na+ and Ca2+ as well as the cellular levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA). Plants with MSB treatment manifested minimal oxidative injury in the form of lower H2O2 and MDA accumulation. This decrease was ascribed to MSB-mediated improvement in the accumulation of antioxidant compounds (anthocyanins, ascorbate, flavonoids, and phenolics) alongside enhanced activities of catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). MSB-treated plants exhibited a maximal improvement in the accretion of total free amino acids and proline under salinity. Foliar spray of MSB at 50 µM effectively protected plants from salinity-induced oxidative damage and specific ion toxicity. Higher salinity tolerance in cv. Shabnam-786 was ascribed to better antioxidant system, lower oxidative damage, and minimal tissue Na+ contents compared with cv. Arka Anamika.