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

Abstract

After a 5-second exposure of illuminated bermudagrass (Cynodon dactylon L. var. 'Coastal') leaves to "CO2, 84% of the incorporated "4C was recovered as aspartate and malate. After transfer from "4C02-air to 'CO2-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.We conclude from the enzyme and '4C-labeling studies that bermudagrass contains the C4-dicarboxylic acid cycle and that pyruvate-phosphate dikinase does not exist exclusively in C4-dicarboxylic acid cycle plants, and we propose that in Cdicarboxylic acid cycle plants the transfer of carbon from a dicarboxylic acid to 3-phosphoglyceric acid involves a decarboxylation reaction and then a refixation of carbon dioxide by ribulose-1,5-diphosphate carboxylase.Previous experiments with isolated chloroplasts from Cynodon dactvlon L. (bermudagrass, var. 'Coastal') leaves indicated an active cyclic and noncyclic photophosphorylation which might meet the ATP requirements for photosynthetic CO2 metabolism in bermudagrass (8). However, the photosynthetic (3,4,7,9,20). This report presents data to establish the pathway of photosynthetic CO2 metabolism in bermudagrass, and comparative data are presented on several other plants which possess either the C4 cycle or the pentose cycle of photosynthesis.

The Distribution of Carbonic Anhydrase and Ribulose Diphosphate Carboxylase in Maize Leaves

“…Total leaf activity for this enzyme averaged 157 p,moles CO2 fixed per mg chlorophyll per hour. This value is similar to those reported by Bjorkman and Gauhl (2) and Chen et al (6) for maize. Recovery of carboxylase activity in the fractions was greater than 90% for both the progressive and differential grinding techniques.…”

Spectral, Physical, and Electron Transport Activities in the Photosynthetic Apparatus of Mesophyll Cells and Bundle Sheath Cells of Digitaria sanguinalis (L.) Scop.

“…Although this hypothesis for C4 cycle photosynthesis may be correct for crabgrass, it appears that other C4 plants such as bermudagrass may lack sufficient malic enzyme to operate this exact cycle and an alternative pathway involving aspartic acid has been proposed (12). During processing of this manuscript the results of an investigation with isolated chloroplasts from C4 plants by Woo et al (35) were published.…”

The Requirement for Sodium as a Micronutrient by Species Having the C4 Dicarboxylic Photosynthetic Pathway

“…This communication gives results of experiments in which six species from five families (Echinochloa utilis, Cynodon dactylon, Kyllinga brevifolia, A maranthus tricolor, Kochia childsii, and Portulaca grandiflora) with features of C, plants (7,9) were shown to have a sodium requirement whereas Poa pratensis, a species with C3 characteristics, showed no response to sodium. These results in conjunction with previously pub- …”