Elevation of cytosolic calcium precedes anoxic gene expression in maize suspension-cultured cells.
Based on pharmacological evidence, we previously proposed that intracellular Ca2+ mediates the perception of O2 deprivation in maize seedlings. Herein, using fluorescence imaging and photometry of Ca2+ in maize suspension-cultured cells, the proposal was further investigated. Two complementary approaches were taken: (1) real time analysis of anoxia-induced changes in cytosolic Ca2+ concentration ([Ca]i) and (2) experimental manipulation of [Ca]i and then assay of the resultant anoxia-specific responses. O2 depletion caused an immediate increase in [Ca2+]i, and this was reversible within a few seconds of reoxygenation. The [Ca]i elevation proceeded independent of extracellular Ca2+. The kinetics of the Ca2+ response showed that it occurred much earlier than any detectable changes in gene expression. Ruthenium red blocked the anoxic [Ca]i elevation and also the induction of adh1 (encoding alcohol dehydrogenase) and sh1 (encoding sucrose synthase) mRNA. Ca2+, when added along with ruthenium red, prevented the effects of the antagonist on the anoxic responses. Verapamil and bepridil failed to block the [Ca]i rise induced by anoxia and were equally ineffective on anoxic gene expression. Caffeine induced an elevation of [Ca]i as well as ADH activity under normoxia. The data provide direct evidence for [Ca]i elevation in maize cells as a result of anoxia-induced mobilization of Ca2+ from intracellular stores. Furthermore, any manipulation that modified the [Ca]i rise brought about a parallel change in the expression of two anoxia-inducible genes. Thus, these results corroborate our proposal that [Ca]i is a physiological transducer of anoxia signals in plants.
Subbaiah
C C
CC
Department of Agronomy, University of Illinois, Urbana 61801.
Bush
D S
DS
Sachs
M M
MM
D000814:Aniline Compounds; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D005456:Fluorescent Dyes; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D010100:Oxygen / Q000378:metabolism*; D014966:Xanthenes; D003313:Zea mays / Q000166:cytology / Q000187:drug effects / Q000235:genetics*
D000814:Aniline Compounds; D002121:Calcium Channel Blockers; D005456:Fluorescent Dyes; D014966:Xanthenes; C059715:Fluo-3; D002110:Caffeine; D010100:Oxygen; D002118:Calcium