Fluctuations in activity of dehydrogenases in leaves of tobacco genotypes as a function of time day and leaf maturity

Abstract

Summary In our search for an explanation of the developmental behavior of a yellow tobacco mutant, Pale yellow, we surveyed the levels of 8 dehydrogenases selected as representative of three major biochemical pathways in plants. Leaves were harvested at three times during the diurnal cycle from three leaf positions on plants of the pale yellow genotype and its green counterpart NC-95 grown in controlled environment chambers. Regardless of genotype, levels of most of the enzymes oscillated during a standard 8-h day and peaked at midday. On the other hand, enzymes varied with maturity of the leaves in the two genotypes. Pale yellow contained higher specific activities in older than in younger leaves, whereas NC-95 showed highest activity in leaves of intermediate maturity. Photosynthetic, glycolytic and Krebs cycle dehydrogenases showed similar trends. The data suggested that the up-the-stalk uniform ripening of Pale yellow tobacco was due in part to an unusually high retention by older leaves of enzymes involved in intermediary metabolism. How the enzymes in question managed to survive senescence is not known.