Photosynthetic 14CO2 Fixation Products and Activities of Enzymes Related to Photosynthesis in Bermudagrass and Other Plants 1

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After a 5-second exposure of illuminated bermudagrass (Cynodon dactylon L. var. `Coastal') leaves to 14CO2, 84% of the incorporated 14C was recovered as aspartate and malate. After transfer from 14CO2-air to 12CO2-air under continuous illumination, total radioactivity decreased in aspartate, increased in 3-phosphoglyceric acid and alanine, and remained relatively constant in malate. Carbon atom 1 of alanine was labeled predominantly, which was interpreted to indicate that alanine was derived from 3-phosphoglyceric acid. The activity of phosphoenolpyruvate carboxylase, alkaline pyrophosphatase, adenylate kinase, pyruvate-phosphate dikinase, and malic enzyme in bermudagrass leaf extracts was distinctly higher than those in fescue (Festuca arundinacea Schreb.), a reductive pentose phosphate cycle plant. Assays of malic enzyme activity indicated that the decarboxylation of malate was favored. Both malic enzyme and NADP+-specific malic dehydrogenase activity were low in bermudagrass compared to sugarcane (Saccharum officinarum L.). The activities of NAD+-specific malic dehydrogenase and acidic pyrophosphatase in leaf extracts were similar among the plant species examined, irrespective of the predominant cycle of photosynthesis. Ribulose-1, 5-diphosphate carboxylase in C4-dicarboxylic acid cycle plant leaf extracts was about 60%, on a chlorophyll basis, of that in reductive pentose phosphate cycle plants.

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