In vitro nitrate reductase activity and in vivo phytochrome measurements of maize seedlings as affected by various light treatments

Concomitant in vivo assays of phytochrome and in vitro assaysof nitrate reductase (NR) were made with mesocotyls of Zea maysL. seedlings. NR assays were also made using the potentiallychlorophyllous portions (leaf and coleoptile) of the same shoots.A negative relationship was found between phytochrome levelsand NR activities in response to various light treatments. Noqualitative differences occurred between the NR responses ofmesocotyl and potentially chlorophyllous or chlorophyllous tissues.Exposure of dark-grown seedlings to continuous white light causedrapid losses of assayable phytochrome accompanied by rapid increasesin NR activities. Subsequent return of the seedlings to darknessproduced increases in assayable phytochrome and decreases inNR activity. A brief, red-light treatment given at the end ofthe white-light treatments resulted in more NR activity andless assayable phytochrome in the subsequent dark period thana treatment with far-red light. These data suggest that modulationof NR activity is not directly influenced by photosyntheticphotoreceptors and that phytochrome is involved in the photocontrolof NR activity. Results also indicate that light quality atthe end of the day influences both night NR activity as wellas time required to reach maximal NR activity during the nextphotoperiod. ¹ Mississippi Agricultural and Forestry Experiment Station cooperating. (Received December 2, 1977; )