PLANT PHYSIOLOGY , Vol 102, Issue 4 1251-1257, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Induction and Turnover of Nitrate Reductase in Zea mays (Influence of NO3-)
X. Z. Li and A. Oaks
Department of Botany, University of Guelph, Guelph, Ontario, Canada N1G 2W1
Zea mays (cv W64A x W182E) was used to investigate the induction and
turnover of nitrate reductase (NR). In our system, 5 or 10 mM KNO3 gave the
best growth over a 6-d growing period. With these NO3- levels, NR reached
steady-state levels after 24 h. For the turnover experiments, the seedlings
were transferred to a NO3--free medium after a 24-h induction. Shoot NR was
less sensitive to the removal of NO3- than root NR, which declined almost
as soon as NO3- was removed when the seedlings were induced with 5 or 10 mM
NO3-. With 1 mM NO3-, however, removal of NO3- from medium resulted in
declines in both NR activity and NO3- in shoot and root. Although there was
a delay in the degradation of NR protein relative to the loss of NR
activity, this protein was not reactivated when NO3- was resupplied. These
results indicate that NO3- regulates NR by influencing the de novo
synthesis of the NR protein and not by a reversible activation-inactivation
of that protein.
