Gueta-Dahan, Y., Department of Plant Sciences, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Avsian-Kretchmer, O., Department of Plant Sciences, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Ben-Hayyim, G., Department of Plant Sciences, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel

Detrimental effects of salinity on plants are known to be partially alleviated by external Ca2+. Previously we demonstrated that in citrus cells, phospholipid hydroperoxide glutathione peroxidase (GPX1) is induced by salt and its activation can be monitored by pGPX1::GUS fusion in transformed tobacco cells. In this paper we further characterized the induction of GPX1 by additional treatments, which are known to affect Ca2+ transport. Omission of Ca2+ changed the pattern of the transient salt-induced expression of GPX1 and chelation of Ca2+ by EGTA, or treatment with caffeine, abolished the salt-induced GPX1 transcript. On the other hand, La3+ was found to be as potent as NaCl in inducing GPX1 transcription and the combined effect of La3+ and NaCl seemed to be additive. Pharmacological perturbation of either external or internal Ca 2+ pools by La3+, EGTA, caffeine, Ca2+ channel blockers, or a Ca2+-ATPase inhibitor rendered the imposed salt stress more severe. Except for La3+, all these Ca2+ effectors had no effect on their own. In addition, the fluidizer benzyl alcohol dramatically increased the NaCl-induced GPX1 transcription. Taken together, our results show that: 1) the mode of action of La3+ on GPX1 expression differs from its established role as a Ca2+ channel blocker, 2) membrane integrity has an important role in the perception of salt stress, and 3) internal stores of Ca2+ are involved in activating GPX1 expression in response to salt stress. We propose that the common basis for these effects lies in the membrane bound Ca2+. © 2008 Springer-Verlag.