PLANT PHYSIOLOGY , Vol 107, Issue 4 1303-1311, Copyright © 1995 by American Society of Plant Biologists
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GENE REGULATION AND MOLECULAR GENETICS |
Expression of NADH-Specific and NAD(P)H-Bispecific Nitrate Reductase Genes in Response to Nitrate in Barley
K. Sueyoshi, A. Kleinhofs and R. L. Warner
Department of Crop and Soil Sciences, Washington State University, Pullman, Washington 99164-6420
Barley (Hordeum vulgare L.) has two, differentially regulated, nitrate
reductase (NR) genes, one encoding the NADH-specific NR (Nar1) and the
other encoding the NAD(P)H-bispecific NR (Nar7). Regulation of the two NR
genes by nitrate was investigated in wild-type Steptoe and in an
NADH-specific NR structural gene mutant (Az12). Gene-specific probes were
used to estimate NADH and NAD(P)H NR mRNAs. The kinetics of induction by
nitrate were similar for the two NR genes; expression was generally below
the limits of detection prior to induction, reached maximum levels after 1
to 2 h of induction in roots and 4 to 8 h of induction in leaves, and then
declined to steady-state levels. Derepression of the NAD(P)H NR gene in
leaves of the NADH-specific NR gene mutant Az12 did not appear to be
associated with changes in nitrate assimilation products or nitrate flux.
Nitrate deprivation resulted in rapid decreases in NADH and NAD(P)H NR
mRNAs in seedling roots and leaves and equally rapid decreases in the
concentration of nitrate in the xylem sap. These results indicate that
factors affecting nitrate uptake and transport could have a direct
influence on NR expression in barley leaves.