Cc. Subbaiah et al., ELEVATION OF CYTOSOLIC CALCIUM PRECEDES ANOXIC GENE-EXPRESSION IN MAIZE SUSPENSION-CULTURED CELLS, The Plant cell, 6(12), 1994, pp. 1747-1762
Based on pharmacological evidence, we previously proposed that intrace
llular Ca2+ mediates the perception of O-2 deprivation in maize seedli
ngs. Herein, using fluorescence imaging and photometry of Ca2+ in maiz
e suspension-cultured cells, the proposal was further investigated. Tw
o complementary approaches were taken: (1) real time analysis of anoxi
a-induced changes in cytosolic Ca2+ concentration ([Ca](i)) and (2) ex
perimental manipulation of [Ca](i) and then assay of the resultant ano
xia-specific responses. O-2 depletion caused an immediate increase in
[Ca](i), and this was reversible within a few seconds of reoxygenation
. The [Ca](i) elevation proceeded independent of extracellular Ca2+. T
he 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 ant
agonist on the anoxic responses. Verapamil and bepridil failed to bloc
k the [Ca](i) rise induced by anoxia and were equally ineffective on a
noxic gene expression. Caffeine induced an elevation of [Ca](i) as wel
l as ADH activity under normoxia, The data provide direct evidence for
[Ca]i elevation in maize cells as a result of anoxia-induced mobiliza
tion 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 corrobor
ate our proposal that [Ca](i) is a physiological transducer of anoxia
signals in plants.