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Plant and Cell Physiology, 1978, Vol. 19, No. 3 481-489
© 1978

Article

In vitro nitrate reductase activity and in vivo phytochrome measurements of maize seedlings as affected by various light treatments1

Stanley H. Duke2 and Stephen O. Duke3

2 Department of Agronomy, University of Wisconsin Madison, WI 53706, U. S. A.
3 USDA/ARS Southern Weed Science Laboratory Stoneville, MS 38776, U. S. A.

Concomitant in vivo assays of phytochrome and in vitro assays of nitrate reductase (NR) were made with mesocotyls of Zea mays L. seedlings. NR assays were also made using the potentially chlorophyllous portions (leaf and coleoptile) of the same shoots. A negative relationship was found between phytochrome levels and NR activities in response to various light treatments. No qualitative differences occurred between the NR responses of mesocotyl and potentially chlorophyllous or chlorophyllous tissues. Exposure of dark-grown seedlings to continuous white light caused rapid losses of assayable phytochrome accompanied by rapid increases in NR activities. Subsequent return of the seedlings to darkness produced increases in assayable phytochrome and decreases in NR activity. A brief, red-light treatment given at the end of the white-light treatments resulted in more NR activity and less assayable phytochrome in the subsequent dark period than a treatment with far-red light. These data suggest that modulation of NR activity is not directly influenced by photosynthetic photoreceptors and that phytochrome is involved in the photocontrol of NR activity. Results also indicate that light quality at the end of the day influences both night NR activity as well as time required to reach maximal NR activity during the next photoperiod.

1 Mississippi Agricultural and Forestry Experiment Station cooperating.

(Received December 2, 1977; )
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