Effect of Chloramphenicol and Cycloheximide on the Induction of Nitrate Reductase and Nitrite Reductase in Bean Leaves

In etiolated leaves of Phaseolus vulgaris L. cv. Prelude only low levels of NADH-nitrate oxidoreductase (E.C. 1.6.6.2; NAR) and reduced benzyl viologen-nitrite oxidoreductase (E.C. 1.6.6.4; NIR) could be detected, even in the presence of nitrate. When nitrate was available illumination of leaves of 10-day-old etiolated seedlings resulted in an induction of both NAR and NIR. In the absence of nitrate no induction of the enzymes took place, although greening of the leaves was normal. Chloramphenicol (CAP) and cycloheximide (CHI), applied at the beginning of the light period, inhibited the induction of both NAR and NIR. Administered after 24 h of illumination CHI still inhibited the induction of both enzymes whereas CAP was no longer inhibitory. The induction of NAR and NIR by nitrate in green leaves in light was inhibited by CHI but not by CAP. From these results it seems likely that both the enzymes NAR and NIR are synthesized on cytoplasmic ribosomes. Before the enzymes can be manufactured in the cytoplasm some chloroplast development is required.