Ca2+ significantly enhanced development and salt-secretion rate of salt glands of Limonium bicolor under NaCl treatment

The divalent cation, Ca2+, plays crucial roles in plant growth, development and stress resistance. Limonium bicolor seedlings were treated with 200 mM NaCl combined with three levels of Ca2+ (0 mM, 5 mM and 20 mM) for 15 days to study the effects of Ca2+ on development and salt-secretion rates of salt glands. It was shown that the 4th leaf areas of L. bicolor seedlings under 20 mM Ca2+ treatment were significantly higher than those under 0 mM and 5 mM Ca2+ treatments. The total number and the densities of salt glands per leaf increased markedly with increased Ca2+ concentrations. The diameters of salt glands increased by 59% and 63% as Ca2+ concentration increased from zero to 5 mM and 20 mM, respectively. Under 20 mM Ca2+ treatment, the salt-secretion rate per leaf was obviously higher than that treated with 5 mM Ca2+, but there was no significant difference in the salt-secretion rates per salt gland between the two groups. Under 0 mM Ca2+ treatment, leaf-cell membrane permeability increased significantly, which led to serious leakage of ions and a significant increase in Na+ loss rate. The results showed that the increase of Ca2+ concentration markedly enhanced development and salt-secretion rates of salt glands in the leaves of L. bicolor, the increase of salt secretion per leaf is due to the efficiency of the secretion process per salt gland and the number of salt glands, the salt-secretion rates per salt gland have a relationship with the diameters of salt glands.