INVOLVEMENT OF INTRACELLULAR CALCIUM IN ANAEROBIC GENE-EXPRESSION ANDSURVIVAL OF MAIZE SEEDLINGS

Ca-mediated processes are known to be involved in transducing many dev elopmental, hormonal, and environmental cues in plant cells. In this s tudy, the role of Ca in the perception of anoxic stress signals by mai ze (Zee mays L. cv B73) roots was assessed by studying the effect of v arious Ca antagonists on the induction of alcohol dehydrogenase (ADH) and sucrose synthase mRNA as well as ADH activity under anoxia. The ef fect of these compounds on the poststress recovery of the seedlings wa s also monitored. Ruthenium red (RR), an inhibitor of organellar Ca fl uxes, repressed the anoxic activation of the alcohol dehydrogenase1 an d shrunken1 genes as measured by their transcript levels as well as AD H activity. Furthermore, RR-treated seedlings could not recover even a fter only 2 h of flooding, in contrast to untreated B73 seedlings that survived 72 h of submergence. Ca, when supplied along with RR, allowe d normal anoxic gene expression and also prevented the RR-imposed deat h of the seedlings from short-term anoxia. Ca (Ca-45) fluxes were meas ured in maize roots to elucidate the mode of action of RR. RR abolishe d anoxia-stimulated Ca-45 influx into maize roots but did not affect a erobic Ca2+ uptake, unlike a few other antagonists that blocked both t he aerobic and anoxic fluxes. However, Ca uptake across the plasma mem brane was not necessary for the adaptive response to anoxia, since che lation of extracellular Ca by ethyleneglycol-bis(beta-aminoethyl ether )-N,N'-tetraacetic acid or 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tet raacetic acid did not affect the induction of ADH activity or poststre ss survival of flooded seedlings. The data suggest that RR may act on one of the intracellular stores of Ca and the Ca mobilized from this s ource is a physiological transducer of anoxic stress signals in maize roots.