Chen J., Xiao Q., Wu F.H., Dong X.J., He J.X., Pei Z.M., Zheng H.L.*Tree Physiology, 2010. 30: 1570-1585.

The modulation of nitric oxide (NO) on ion homeostasis, by enhancing the salt secretion in the salt glands and Na⁺sequestration into the vacuoles, were investigated in a salt-secreting mangrove tree,Avicennia marina(Forsk.) Vierh. The major results are as follows. (1) Under 400 mM NaCl treatment, the application of 100 μM sodium nitroprusside (SNP), a NO donor, significantly increased the density of salt crystals and salt secretion rate of the leaves, along with maintaining a low Na⁺to K⁺ratio in the leaves. (2) The element contents measurements by X-ray microanalysis in the epidermis and transversal sections ofA. marinaleaves revealed that SNP (100 μM) significantly increased the accumulation of Na⁺in the epidermis and hypodermal cells, particularly the Na⁺to K⁺ratio in the salt glands, but no such effects were observed in the mesophyll cells. (3) Using the Non-Invasive Micro-Test Technology (NMT), both long-term SNP (100 μM) and transient SNP (30 μM) treatments significantly increased the net Na⁺efflux in the salt glands. On the contrary, NO synthesis inhibitors and scavenger reversed the effects of NO on Na⁺flux. These results indicate that NO enhanced the salt secretion by increasing the net Na⁺efflux in the salt glands. (4) Western-blot analysis demonstrated that 100 μM SNP stimulated the protein expressions of plasma membrane (PM) H⁺-ATPase and vacuolar membrane Na⁺/H⁺antiporter. (5) To further clarify the molecular mechanism of the effects of NO on enhancing salt secretion and Na⁺sequestration, the partial cDNA fragments of PM H⁺-ATPase (HA1), PM Na⁺/H⁺antiporter (SOS1) and vacuolar Na⁺/H⁺antiporter (NHX1) were isolated and the transcriptional expression ofHA1,SOS1,NHX1and vacuolar H⁺-ATPase subunit c (VHA-c1) genes were analyzed using real-time quantitative PCR. The relative transcript abundances of the four genes were markedly increased in 100 μM SNP-treatedA. marina. Moreover, the increases were reversed by NO synthesis inhibitors and scavenger. Taken together, our results strongly suggest that the NO functions as a signal in salt resistance ofA. marinaby enhancing the salt secretion and Na⁺sequestration, which are dependent on the increased expression of the H⁺-ATPase and Na⁺/H⁺antiporter.