Antioxidant capacity, photosynthetic characteristics and water relations of sunflower (Helianthus annuus L.) cultivars in response to drought stress

Plant species and cultivars have different physiological mechanisms in response to drought stress. A biennial field experiment was conducted to evaluate the effect of drought severities on enzymatic and non-enzymatic antioxidants, photosynthetic pigments, chlorophyll florescence and water relations in sunflower cultivars. Eight cultivars of sunflower (Azargol, Iroflor, Armavirovski, Lakumka, Alstar, Master, Sirna and Pumar) were subjected to well-watered, moderate and severe drought stress. Drought treatments were started at the beginning of stem elongation. The results showed that catalase activity, carotenoid content, proline content and electrolyte leakage were increased with drought severity, but chlorophyll-a, chlorophyll-b, maximum photochemical efficiency of photosystem-II, photosynthetic performance index, relative water content, and stomatal conductance were decreased. Peroxidase activity was not affected by drought stress. There was a positive correlation between enzymatic and non-enzymatic antioxidants. Catalase activity was correlated positively with proline content but negatively with chlorophyll content and chlorophyll florescence. Carotenoid had a negative correlation with chlorophyll-a as well as chlorophyll-b, but had a positive correlation with proline content.