Increasing Ca Accumulation in Salt Glands Under Salt Stress Increases Stronger Selective Secretion of Na in Tetraploids

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 content on Na and K secretion were investigated in diploid and tetraploid P. auriculata under salt stress. Salt gland Ca content and secretion rates of Na and K were higher in tetraploids than in diploids under salt stress. Addition of exogenous Ca increased the Ca 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 channel inhibitor, diploid salt glands retained large amounts of Ca, leading to higher Ca content and Na secretion rate than those of tetraploids. Inhibiting HO 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 content in salt gland.