The effects of chloramphenicol, cycloheximide and kinetin on the changes in activity of glutamate dehydrogenase (GDH), glutamate pyruvate transaminase (GPT), glutamate oxaloacetate transaminase (GOT) and nitrite reductase were studied during the senescence of detached barley leaves in the light and dark. The four enzymes seemed to be synthesized at least during the first hours of senescence. The rate of synthesis of GDH was clearly higher than that of its degradation, thus continuously increasing during senescence. Chloramphenicol and kinetin delayed the enzyme degradation processes of senescence in the dark. However, chloramphenicol accelerated senescence in the light. Kinetin had no significant effect on the enzyme activities in the light. Cycloheximide treatments produced lower enzyme levels than their respective controls in both the light and dark, but the enzyme levels were higher in cycloheximide treated leaves in the light than in the controls in water in the dark. The results are discussed with reference to the requirement for protein synthesis in the different processes of senescence.
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