PLANT PHYSIOLOGY , Vol 112, Issue 3 1015-1022, Copyright © 1996 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Characterization of Hypoxically Inducible Lactate Dehydrogenase in Maize
M. E. Christopher and A. G. Good
Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada T6G 2E9
Oxygen deprivation induces a wide variety of genes, but the most
extensively studied are those encoding enzymes of the glycolytic pathway.
Lactate dehydrogenase (LDH, EC 1.1.1.27) activity increases up to 3.5-fold
in maize (Zea mays L.) roots during several days of hypoxic induction. This
increase in activity is accompanied by a decrease in in vitro enzyme
stability. LDH activity in aerobic root extracts has an in vitro half-life
of 240 min, decreasing to 100 min in 72-h hypoxically induced plant root
extracts. The increase in enzyme activity during hypoxic induction is the
result of increased protein levels, which correlate with increased
transcript levels. Two ldh transcripts of 1.3 and 1.7 kb are induced, with
maximum levels reached by 8 and 24 h, respectively. This suggests that the
two ldh genes are differentially regulated. Treatment with the protein
synthesis inhibitor cycloheximide does not preclude ldh induction during
the first few hours of hypoxic stress, suggesting that new protein
synthesis may not be essential for elevation of ldh transcript levels under
hypoxic conditions. The rapid and substantial increase in ldh mRNA levels
under hypoxic conditions and in the presence of cycloheximide suggests that
the ldh gene may be valuable in analyzing the hypoxic signal transduction
pathway.
