Oxidative Stress-Induced Calcium Signaling in Arabidopsis

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Abstract
Many environmental stresses result in increased generation of active oxygen species in plant cells. This leads to the induction of protective mechanisms, including changes in gene expression, which lead to antioxidant activity, the recovery of redox balance, and recovery from damage/toxicity. Relatively little is known about the signaling events that link perception of increased active oxygen species levels to gene expression in plants. We have investigated the role of calcium signaling in H2O2-induced expression of the GLUTATHIONE-S-TRANSFERASE1 (GST1) gene. Challenge with H2O2 triggered a biphasic Ca2+ elevation in Arabidopsis seedlings. The early Ca2+ peak localized to the cotyledons, whereas the late Ca2+ rise was restricted to the root. The two phases of the Ca2+ response were independent of each other, as shown by severing shoot from root tissues before H2O2 challenge. Modulation of the height of Ca2+ rises had a corresponding effect upon H2O2-induced GST1 expression. Application of the calcium channel blocker lanthanum reduced the height of the first Ca2+ peak and concomitantly inhibited GST1 expression. Conversely, enhancing the height of the H2O2-triggered Ca2+ signature by treatment with L-buthionine-[S,R]-sulfoximine (an inhibitor of glutathione synthesis) lead to enhancement of GST1 induction. This finding also indicates that changes in the cellular redox balance constitute an early event in H2O2 signal transduction as reduction of the cellular redox buffer and thus the cell's ability to maintain a high GSH/GSSG ratio potentiated the plant's antioxidant response.