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Articles

Synthesis and Degradation of Barley Nitrate Reductase ¹

Department of Agronomy and Soils and Program in Genetics and Cell Biology, Washington State University, Pullman, Washington 99164-6420

Nitrate and light are known to modulate barley (Hordeum vulgare L.) nitrate reductase activity. The objective of this investigation was to determine whether barley nitrate reductase is regulated by enzyme synthesis and degradation or by an activation-inactivation mechanism. Barley seedling nitrate reductase protein (cross-reacting material) was determined by rocket immunoelectrophoresis and a qualitative immunochemical technique (western blot) during the induction and decay of nitrate reductase activity. Nitrate reductase cross-reacting material was not detected in root or shoot extracts from seedlings grown without nitrate. Low levels of nitrate reductase activity and cross-reacting material were observed in leaf extracts from plants grown on nitrate in the dark. Upon nitrate induction or transfer of nitrate-grown etiolated plants to the light, increases in nitrate reductase activity were positively correlated with increases in immunological cross-reactivity. Root and shoot nitrate reductase activity and cross-reacting material decreased when nitrate-induced seedlings were transferred to a nitrate-free nutrient solution or from light to darkness. These results indicate that barley nitrate reductase levels are regulated by de novo synthesis and protein degradation.

³ To whom reprint requests should be addressed.

⁴ Department of Biology, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1 Canada.

¹ Supported in part by National Science Foundation grant PCM 81-19096 and United States Department of Agriculture Competitive Research Grants Office grant 79-00536. Scientific Paper No. 6385, College of Agriculture Research Center, Washington State University, Pullman, WA. Project Nos. 0430 and 0233.

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