Exogenous 6-BA enhances salt tolerance of Limonium bicolor by increasing the number of salt glands.

Exogenous 6-BA can increase endogenous hormone content, improve photosynthesis, decrease Na by increasing leaf salt gland density and salt secretion ability, and reduce ROS content so that it can promote L. bicolor growth. 6-benzyl adenine (6-BA) is an artificial cytokinin and has been widely applied to improving plant adaptation to stress. However, it is rarely reported that 6-BA alleviates salt damage of halophytes. In this paper, we treated Limonium bicolor seedlings, a recretohalophyte with high medicinal and ornamental values, with 300 mM NaCl and different concentrations of 6-BA (0.5, 1.0, and 1.5 mg/L) and measured plant growth, physiological index, the density of salt gland, and the salt secretion ability of leaves. The results showed that exogenous applications 1.0 mg/L 6-BA significantly improved plant growth and photosynthesis, increased cytokinin and auxins contents, K and organic soluble matter contents, the activities of SOD, CAT, APX, and POD, and decreased Na, HO, and O contents compared to that treated with 300 mM NaCl. Further research showed that exogenous 6-BA significantly increased the density of salt gland and the salt secretion ability of leaves by upregulating the expression of the salt gland developmental genes, therefore, can secrete more excess Na, and thus reduces the Na concentration in leaves, which can alleviate Na damage to the species. In all, exogenous 1.0 mg/L 6-BA can increase endogenous hormone, improve photosynthesis, decrease Na by increasing secretion ability, and reduce ROS content of L. bicolor so that it can improve the growth. These results above systematically prove the new role of 6-BA in salt tolerance of L. bicolor.