Chitosan effects on physiochemical indicators of drought-induced leaf stress in cowpea

Abstract

Water deficit stress in crops is associated a damaging oxidative process that is irreversible once it is initiated. This study was conducted to assess the effect of chitosan, a marine polysaccharide with unique bioactive properties that scavenges for reactive oxygen species; hence, chitosan application to plants has been suggested as an aid for reducing oxidative injury caused by water deficit stress. In a greenhouse, potted cowpea plants, Vigna unguiculata (L.) Walp. (var. Cream 7), were subject to 12 treatments comprised of 70% (low water deficit stress, control), 50% (moderate stress), and 30% (high stress) field capacity irrigation regimes that were sprayed at the initiation of flowering with 0, 125, 250, and 500 mg/l chitosan. Chitosan application reduced hydrogen peroxide (H2O2) accumulation by as much as 37%, lipid peroxidation by as much as 57%, and membrane permeability by up to 16% in leaves from plants under high water deficit stress. The application of chitosan also elevated antioxidant enzyme activities, such as superoxide dismutase by up to 85% and catalase by up to 37%, and accumulations of ascorbic acid, calcium, carotenoids, magnesium, and phenolic compounds that were up to 204%, 29%, 193%, 27%, and 83%, respectively, over leaves of nonsprayed mature plants. Under moderate and severe water deficit, chitosan, particularly at a concentration of 250 mg/liter water, decreased physiochemical indicators of drought stress in leaves, and increased indicators of stress reduction. The greater levels of antioxidants and low H2O2 concentration in the chitosan-treated cowpea leaves suggest that chitosan delays effects of water deficit stress. Chitosan might be useful for crop production in situations where water availability is limited, and to make crop plants less attractive to pests that are favored by water deficit stressed plants.