Plant Physiol.
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Plant Physiology 70:35-38 (1982)
© 1982 American Society of Plant Biologists

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Differential Effect of Tungsten on the Development of Endogenous and Nitrate-Induced Nitrate Reductase Activities in Soybean Leaves 1

Muhammad Aslam2

Crop Science Section, Agriculture Canada Research Station, Harrow, Ontario, Canada N0R 1G0

The effect of tungsten on the development of endogenous and nitrate-induced NADH- and FMNH2-linked nitrate reductase activities in primary leaves of 10-day-old soybean (Glycine max [L.] Merr.) seedlings was studied. The seedlings were grown with or without exogenous nitrate. High levels of endogenous nitrate reductase activities developed in leaves of seedlings grown without nitrate. However, no endogenous nitrite reductase activity was detected in such seedlings. The FMNH2-linked nitrate reductase activity was about 40% of NADH-linked activity. Tungsten had little or no effect on the development of endogenous NADH- and FMNH2-linked nitrate reductase activities, respectively. By contrast, in nitrate-grown seedlings, tungsten only inhibited the nitrate-induced portion of NADH-linked nitrate reductase activity, whereas the FMNH2-linked activity was inhibited completely. Tungsten had no effect on the development of nitrate-induced nitrite reductase activity. The complete inhibition of FMNH2-linked nitrate reductase activity by tungsten in nitrate-grown plants was apparently an artifact caused by the reduction of nitrite by nitrite reductase in the assay system. The results suggest that in soybean leaves either the endogenous nitrate reductase does not require molybdenum or the molybdenum present in the seed is preferentially utilized by the enzyme complex as compared to nitrate-induced nitrate reductase.

2 Present address: Plant Growth Laboratory, University of California, Davis, CA 95616.

1 During these studies, the author was the recipient of a visiting fellowship from the Natural Sciences and Engineering Research Council of Canada.






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