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Genetic Variation in Enzyme Activity of Tall Fescue Leaf Blades¹

Plants show genetic variation in several physiological responses that involve enzymes. Our objective was to determine if genetic variation existed in some representative metabolic enzymes of tall fescue (Festuca arundinacea Schreb.). Fully developed leaves from 12 genotypes selected from six diverse populations growing in the field were sampled for activity of eight enzymes. Genetic differences were found for activities of all enzymes studied and often between genotypes from the same population. Expressing enzyme activity on a fresh weight, dry weight, or leaf area basis gave better discrimination between genotypes than expressing on a Lowry protein basis.

Activities of ribulose 1, 5-diphosphate carboxylase (RuDPc), phosphoenolpyruvate carboxylase (PEPc), and alanine aminotransferase (GPT) were positively correlated among genotypes. Phosphoglyceryl kinase (PGK) activity was correlated with RuDPc, GPT, and glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Also, activities of malate dehydrogenase (MDH) and GAPDH were positively correlated with those of RuDPc and PEPc. Isocitrate dehydrogenase had a lower relative activity, but was positively correlated with MDH and GAPDH, two other respiratory enzymes. Activity of glucose 6-phosphate dehydrogenase, an enzyme of the oxidative pentosephosphate pathway, was not correlated with that of any other enzyme studied. It is apparent that genetic variation exists, and that genetic studies of enzyme activity will become increasingly more important as rate-limiting steps in growth and metabolism of crop plants become clarified.

Key Words: Photosynthetic enzymes • Respiratory enzymes • Transaminase • Base of expression • Festuca arundinacea Schreb.

² Associate professor, Dept. of Agronomy, Univ. of Missouri, Columbia, MO 65201; principal scientific officer (now plant physiologist, International Institute of Tropical Agricultural, Ibadan, Nigeria); and scientific officer, Welsh Plant Breeding Stn., Aberystwyth, U. K., respectively.

Received for publication November 14, 1974.