DIURNAL-VARIATIONS OF CORN LEAF NITRATE REDUCTASE - AN EXPERIMENTAL DISTINCTION BETWEEN TRANSCRIPTIONAL AND POSTTRANSCRIPTIONAL CONTROL

In leaves of corn (Zea mays L.) a rapid increase in nitrate reductase (EC 1.6.6.1) mRNA was observed during the first hour of illumination in the morning, quickly followed by a decrease in nitrate reductase mRNA. Nitrate reductase activity and protein also increased when the light was turned on. The experiments show that increase in nitrate reductase mRNA levels can be explained, at least partially, by an increased transcriptional activity. When plants were grown at lower temperatures (20-degrees-C), evidence for the involvement of post-translational control of diurnal variations of nitrate reductase activity was found, while at higher temperatures (30-degrees-C) such a post-translational control could not be detected.