PLANT PHYSIOLOGY , Vol 115, Issue 3 1109-1117, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
RNase Activities Are Reduced Concomitantly with Conservation of Total Cellular RNA and Ribosomes in O2-Deprived Seedling Roots of Maize
S. L. Fennoy, S. Jayachandran and J. Bailey-Serres
Department of Botany and Plant Sciences, University of California, Riverside, California 92521-0124
The effect of O2 deprivation on the activities of RNases and levels of
total cellular RNA and ribosomes in seedling roots of maize (Zea mays L.)
was investigated. Sodium dodecyl sulfate-polyacrylamide gels containing RNA
were used to distinguish RNase isoenzymes by apparent molecular mass. Since
O2 deprivation causes a decrease in cytosolic pH from approximately pH 7.4
to 6.4 and an elevation in cytosolic Ca2+, RNase levels were examined in
the physiological range of cytosolic pH and in the presence of Ca2+, Mg2+,
Zn2+, ethylenediaminetetracetate, or ethyleneglycol-bis([beta]-aminoethyl
ether)-N,N[prime]-tetraacetic acid. The activity of a number of RNases
present in aerobic roots was reduced in response to O2 deprivation. Several
RNases with a pH optimum of 6.4 were rapidly down-regulated by O2
deprivation. Spectrophotometric assay of extracts revealed that RNase
activity was higher at pH 6.4 than at 7.2, and
ethylenediaminetetracetate-insensitive RNase activity decreased in response
to O2 deprivation. The decrease in RNase activity was correlated with no
loss of total cellular RNA or ribosomes, despite a 4-fold decrease in
run-on transcription of rRNA in isolated nuclei. Regulation of RNase
activity may facilitate the conservation of nontranslating ribosomes and
poorly translated mRNAs during O2 deprivation.
