Effect of salinity on distribution of ions in mini-watermelon seedlings

A hydroponic cultivation experiment was carried out with two miniwatermelon cultivars differing in salt tolerance to study the effect of different NaCl concentrations on ions distribution in watermelon seedlings. The results show that NaCl stress inhibits the growth of watermelon seedlings, and the extent of inhibition for Xiuya is less than that of Xiuli. Increasing NaCl concentration, the Na+ and Cl- contents of the seedlings are increased, while the K+, Ca2+ and Mg2+ contents decreased. The five ions present a compartmentalized distribution. Cl- mainly accumulates in the stems and Na+ mainly concentrates in roots and stems. The decreased range of the K+ contents is larger in stems and smaller in leaves, Ca2+ and Mg2+ mainly exist in stems and leaves and the declined extent in leaves is less. The abilities of selective transportation of K+ and Ca2+ from roots to stems are decreased, while the abilities from stems to leaves are increased under the NaCl stress, which contributes to alleviate the damage of NaCl stress to leaves. Compared to cv. Xiuli, the K+ and Ca2+ contents in leaves of cv. Xiuya reduced less, Cl- and Na+ accumulations are less. As a consequence, K+/Na+ and Ca2+/Na+ radios are higher, and SK，Na and SCa，Na ratios of selective transportations from stems to leaves are also higher. This research reveals that lower selective transportation of Na+ to leaves is one of main reasons for cv. Xiuya with more salttolerance, and the compartmentalized distribution of ions on the organs is one of physiological adaptation mechanisms of watermelon plants to salinity.