Nitrate reductase-deficient mutants in barley : immunoelectrophoretic characterization

Area of Science:

• Plant molecular biology
• Biochemistry
• Genetics

Background:

• Nitrate reductase is a key enzyme in plant nitrogen assimilation.
• Molybdenum cofactor is essential for nitrate reductase activity.
• Barley mutants deficient in nitrate reductase provide tools to study enzyme function.

Purpose of the Study:

• To characterize nitrate reductase-deficient barley mutants.
• To determine the genetic basis of nitrate reductase deficiency.
• To investigate the role of molybdenum cofactor in nitrate reductase function.

Main Methods:

• Assay of xanthine dehydrogenase activity to assess molybdenum cofactor presence.
• Measurement of nitrate reductase-associated activities.
• Rocket immunoelectrophoresis to detect nitrate reductase cross-reacting material.

Main Results:

• Mutants exhibited a range of nitrate reductase cross-reacting material levels, correlated with enzyme activity.
• Some nar 1 mutants showed structural homology to wild-type nitrate reductase, while others had modified structures.
• Mutants nar 2a, Xno 18, and Xno 19 lacked xanthine dehydrogenase activity, indicating molybdenum cofactor deficiency.

Conclusions:

• The nar 1 gene is likely the structural gene for nitrate reductase in barley.
• Molybdenum cofactor is essential for nitrate reductase function.
• Nitrate reductase is synthesized de novo in response to nitrate induction.