Increasing Ca2+ accumulation in salt glands under salt stress increases stronger selective secretion of Na+ in Plumbago auriculata tetraploids

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 Ca²⁺ content on Na⁺ and K⁺ secretion were investigated in diploid and tetraploid P. auriculata under salt stress. Salt gland Ca²⁺ content and secretion rates of Na⁺ and K⁺ were higher in tetraploids than in diploids under salt stress. Addition of exogenous Ca²⁺ increased the Ca²⁺ 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 Ca²⁺ channel inhibitor, diploid salt glands retained large amounts of Ca²⁺, leading to higher Ca²⁺ content and Na⁺ secretion rate than those of tetraploids. Inhibiting H₂O₂ 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 Ca²⁺ content in salt gland.

Keywords: recretohalophyte; salt gland; salt stress; selective secretion; tetraploid.