Abstract
Under salt stress, recretohalophyte Plumbago auriculata tetraploids enhance salt tolerance by increasing selective secretion of Na(+) compared with that in diploids, although the mechanism is unclear. Using non-invasive micro-test technology, the effect of salt gland Ca(2+) content on Na(+) and K(+) secretion were investigated in diploid and tetraploid P. auriculata under salt stress. Salt gland Ca(2+) content and secretion rates of Na(+) and K(+) were higher in tetraploids than in diploids under salt stress. Addition of exogenous Ca(2+) increased the Ca(2+) content of the salt gland in diploids and is accompanied by an increase in the rate of Na(+) and K(+) secretion. With addition of a Ca(2+) channel inhibitor, diploid salt glands retained large amounts of Ca(2+), leading to higher Ca(2+) content and Na(+) secretion rate than those of tetraploids. Inhibiting H(2)O(2) generation and H(+)-ATPase activity altered Na(+) and K(+) secretion rates in diploids and tetraploids under salt stress, indicating involvement in regulating Na(+) and K(+) secretion. Our results indicate that the increased Na(+) secretion rate of salt gland in tetraploids under salt stress was associated with elevated Ca(2+) content in salt gland.