PLANT PHYSIOLOGY , Vol 101, Issue 2 407-414, Copyright © 1993 by American Society of Plant Biologists
|
ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Hypoxic and Anoxic Induction of Alcohol Dehydrogenase in Roots and Shoots of Seedlings of Zea mays (Adh Transcripts and Enzyme Activity)
D. L. Andrews, B. G. Cobb, J. R. Johnson and M. C. Drew
Department of Horticultural Science, Texas A&M University, College Station, Texas 77843-2133
Alcohol dehydrogenase (ADH) is one of a number of enzymes of glycolysis and
fermentation known to be synthesized preferentially under low O2
conditions. We examined levels of Adh1 transcripts and of ADH activity in
5-mm root tips, root axes (the remainder of the seminal root), and shoots
of maize (Zea mays L. cv TX 5855) seedlings. Seedlings with roots averaging
about 60-mm long were transferred from fully aerobic conditions (solutions
sparged with 40% [v/v] O2) to anaerobic (O2-free) conditions, or to an
intermediate O2 concentration. There was no prior acclimation to low O2. In
root tips, anoxia induced Adh1 transcripts and enzyme activity at 6 h, but
this was followed by a rapid decline so that at 12 to 18 h neither were
detectable and the root tips were dead. In contrast, higher levels of Adh1
transcripts and enzyme activity were maintained for at least 48 h in root
axes and shoots. When induction at 6 h was measured over a wide range of O2
concentrations, a peak in ADH activity occurred in all tissues at 4% (v/v)
O2. Maximum levels of transcripts, however, were in the range of 0 to 4%
O2, depending on the tissue. The time course of hypoxic induction (at 4%
O2) in root tips showed a peak in transcript levels at 6 h, whereas ADH
activity continued to rise throughout the 24-h experiment. These results
show that in root tips, ADH induction by anoxia was small and transient
relative to induction by hypoxia.