Chitosan alleviates phytotoxicity caused by boron through augmented polyamine metabolism and antioxidant activities and reduced boron concentration in Cucumis sativus L.

Abstract

The aim of this investigation was to study an association among boron-induced oxidative stress, antioxidant system and polyamine metabolism in cucumber Cucumis sativus (L) plants. Furthermore, it was also investigated whether chitosan would increase the antioxidant activity and polyamine concentration that could induce tolerance to boron-induced oxidative stress. Cucumber (cv. Sahil) plants were exposed to 0.5, 1.0, and 1.5 mM boron stress at the 16-day stage for one week while receiving nutrient solution. At the 23- and 27-day stages, plants were foliar-treated with chitosan solution (50 and 75 mg L−1), and harvested at the 34-day stage to investigate growth, photosynthesis, and biochemical characteristics. Boron stress significantly reduced the growth, total chlorophyll concentration, relative water contents, photosynthesis, stomatal conductance, internal CO2 concentration, stomatal size, and membrane stability index. However, boron stress elevated the enzymatic activities of various antioxidants, osmolytes, polyamine concentration, H2O2 concentration, lipid peroxidation and electrolyte leakage in leaves. The follow-up spray with chitosan to the plants subjected to boron stress improved growth, relative water contents, green pigments, photosynthetic activity and membrane stability index, and further enhanced the activity of antioxidant enzymes, osmolytes, leaf polyamine concentration, hydrogen peroxide concentration, lipid peroxidation, and electrolyte leakage in the leaves. The augmented level of antioxidant enzymes, root/shoot osmolytes and leaf polyamine concentration might have induced resistance to the boron stressed plants, causing an ameliorated growth, relative water contents, and photosynthesis related characteristics. It is also concluded that chitosan is an eco-friendly alleviator of toxicity caused by boron by enhancing polyamine concentration and strengthening antioxidant defensive system but reducing the boron concentration in plant tissues.