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The involvement of calcium in the regulation of GPX1 expression

Gueta-Dahan, Yardena, Avsian-Kretchmer, Orna, Ben-Hayyim, Gozal
Planta 2008 v.228 no.5 pp. 725-734
mechanism of action, caffeine, tobacco, salinity, calcium, stress response, phospholipid-hydroperoxide glutathione peroxidase, sodium chloride, Citrus, benzyl alcohol, salt stress, chelation, ethylene glycol tetraacetic acid
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 Ca²⁺ 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⁺.