Response of grafted cucumber to specific ion (Na plus , Cl-) under salt stress

To test whether the increased salt tolerance of cucumber grafted onto rootstock was mainly associated with sodium toxicity, cucumber (Cucumis sativus L.cv. Jinchun No. 2) plants, either self-grafted or grafted onto the Figleaf gourd (Cucurbita ficifolia Bouche), were subjected to iso-osmotic Na+, Cl- and NaCl stress, and the plant growth and physiological parameters were measured. The results showed that Na+ salt and NaCl stress significantly decreased the growth of self-grafted and grafted cucumber seedlings. However, plant dry weight, shoot water content, shoot K+ and Ca2+ content, superoxidase dismutase (SOD) activity and chlorophyll content of grafted plants were significantly higher than those of self-grafted plants. Meanwhile, the shoot Na+ content and Na+/K+ ratio of grafted plants were lower than those of self-grafted plants. Compared with the plants under Na+ salt and NaCl stress conditions, smaller change in plant growth and physiological response were observed in the self-grafted and grafted cucumber plants under Cl- stress. Therefore, the sensitivity of self-grafted and grafted plants to Na+ and Cl- is different, and toxicity to cucumber seedlings caused by Na+ is much higher than that of Cl-. Taken together, the improved salt tolerance of cucumber plants grafted onto Figleaf gourd was mainly achieved by reducing the absorption of Na+ and limiting the translocation of Na+ to the shoot.