Effect of salt stress on growth, antioxidant enzymes activity, lipid peroxidation and photosystem II efficiency in cucumber grafted on cucurbit rootstock

Salinity is considered as one of the major abiotic stress limiting growth and productivity of plants. Identification of physiological and biochemical mechanisms involved in the resistance to salinity can be useful to select salt tolerant rootstocks. For this purpose, an experiment was conducted to investigate the effects of rootstock (three cucurbit rootstock, Shintoza, Cobalt, Rootpower) and salinity stress (0, 40, 60 and 80 mM NaCl) on growth, yield, leaf area, antioxidant enzymes activity, malondialdehyde (MDA) content and Photosynthetic parameters in cucumber (cv. Khasib) leaves were determined, 35 days after salt treatments. Plant Growth parameters in all salinity treatments were significantly higher in grafted plants than non-grafted plants. Grafted plants had 14-21% higher yield than non-grafted plants. The catalase (CAT), ascorbate peroxidase (APX), polyphenol oxidase (PPO) and peroxidase (POD) activity increased as a result of salinity stress, but this increase in grafted plant was 0.1-2 times of ungrafted plant. Reductions in stomatal conductance at the three salt treatments were significantly lower in the grafted plants in comparison to ungrafted plants. Moreover, lipid peroxidation (MDA content) in grafted plants was 7-12% less than ungrafted plants by salt stress. Maximal quantum yield of PS II (Fv/Fm) of cucumber leaves showed significant difference between grafted and ungrafted plant and this amount was 3-6 percent more than ungrafted plants. Results suggested that increase in activity of antioxidant enzymes, ratio of Fv/Fm and stomatal conductance in grafted plant could be associated with their greater tolerance to salinity stress.