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Plant Physiology 64:439-444 (1979)
© 1979 American Society of Plant Biologists

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Articles

In Vitro Stability of Nitrate Reductase from Wheat Leaves

II. Isolation of Factors from Crude Extract Which Affect Stability of Highly Purified Nitrate Reductase 1

Joseph H. Sherrard2, Jillian A. Kennedy and Michael J. Dalling

a Plant Sciences Section, School of Agriculture and Forestry, University of Melbourne, Parkville Victoria 3052 Australia

When a crude extract from 8-day-old wheat (Triticum aestivum L. cv. Olympic) leaves was fractionated by a combination of ammonium sulfate precipitation and Sephadex G-100 chromatography the presence of three factors which have a marked effect on the stability of highly purified nitrate reductase was revealed. Two of these factors (I and III) have a positive effect and the other factor (II) has a negative effect on stability. Factors I and III can each overcome the instability-promoting effect of II; however, this was apparently not due to a direct effect on factor II.

Both factors I and III have been subjected to further purification. Factor I can be separated into at least four fractions, each with stability-promoting activity. Factor III appears to be a single factor.

The in vitro activity and stability of nitrate reductase in crude extracts were found to vary diurnally. Stability and activity were highest 4 hours after the start of the light period and both were minimal 1 to 3 hours after the end of the light period. When crude extract was fractionated as described above and an assessment made of the relative amounts of I, II, and III, there appeared to be a distinct diurnal variation in their levels. Factors I and III were highest when in vitro nitrate reductase activity and stability were highest. Factor II was apparently out of phase in that maximum activity coincided with the time of minimum in vitro nitrate reductase activity and stability.

2 Present address: Department of Agronomy, University of Illinois, Urabana Illinois 61801.

1 This work was supported by the Wheat Industry Research Council of Australia and the Australian Research Grants Committee D2 74/15052.






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ASPB Publications PLANT PHYSIOLOGY THE PLANT CELL
Copyright © 1979 by the American Society of Plant Biologists