Distribution of enzymes in mesophyll and parenchyma-sheath chloroplasts of maize leaves in relation to the C4-dicarboxylic acid pathway of photosynthesis

Abstract

1. Mesophyll and parenchyma-sheath chloroplasts of maize leaves were separated by density fractionation in non-aqueous media. 2. An investigation of the distribution of photosynthetic enzymes indicated that the mesophyll chloroplasts probably contain the entire leaf complement of pyruvate,P(i) dikinase, NADP-specific malate dehydrogenase, glycerate kinase and nitrite reductase and most of the adenylate kinase and pyrophosphatase. The fractionation pattern of phosphopyruvate carboxylase suggested that this enzyme may be associated with the bounding membrane of mesophyll chloroplasts. 3. Ribulose diphosphate carboxylase, ribose phosphate isomerase, phosphoribulokinase, fructose diphosphate aldolase, alkaline fructose diphosphatase and NADP-specific ;malic' enzyme appear to be wholly localized in the parenchyma-sheath chloroplasts. Phosphoglycerate kinase and NADP-specific glyceraldehyde phosphate dehydrogenase, on the other hand, are distributed approximately equally between the two types of chloroplast. 4. After exposure of illuminated leaves to (14)CO(2) for 25sec., labelled malate, aspartate and 3-phosphoglycerate had similar fractionation patterns, and a large proportion of each was isolated with mesophyll chloroplasts. Labelled fructose phosphates and ribulose phosphates were mainly isolated in fractions containing parenchyma-sheath chloroplasts, and dihydroxyacetone phosphate had a fractionation pattern intermediate between those of C(4) dicarboxylic acids and sugar phosphates. 6. These results indicate that the mesophyll and parenchyma-sheath chloroplasts have a co-operative function in the operation of the C(4)-dicarboxylic acid pathway. Possible routes for the transfer of carbon from C(4) dicarboxylic acids to sugars are discussed.

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

“…However, the strongest evidence for the C4 cycle has been derived from the demonstration of enzymes activities at levels sufficient for the partial operation of the C4 cycle (2,11,(15)(16)(17)(23)(24)(25)(26) (20-25 C) for photosynthesis (9).…”

Plants under Climatic Stress

“…Previously published methods shown in parentheses were used to assay the following enzymes: pyruvate Pi dikinase (1, assays 1 and 2); P-pyruvate carboxylase, RuDP carboxylase, NADP-malate dehydrogenase, NADP-glyceraldehyde-3-P-dehydrogenase, fructose-1,6-diP aldolase, adenylate kinase and pyrophosphatase (19); alanine aminotransferase and aspartate aminotransferase (2); and carbonic anhydrase (8). Catalase was assayed in centrifuged homogenates of 1 g of leaf lamina in 5 ml of 50 mM phosphate buffer (pH 7.0).…”

“…Temperature of the reaction mixture was regulated by circulating water from a temperature-controlled bath through the cuvette holder and monitored during each assay by a thermocouple inserted into the cuvette. Temperature effects on the activity of PEP-carboxylase and pyruvate Pi dikinase in uncentrifuged Sephadex eluates were assayed using radioactive methods (1,19). The control of temperature required for these assays and measurements of the in vitro activation of pyruvate Pi dikinase and NADP-malate dehydrogenase were achieved using a series of aluminum blocks cooled by circulating chilled water and heated proportionally through silicone controlled rectifiers.…”

Use of Silica Sol Step Gradients to Prepare Bundle Sheath and Mesophyll Chloroplasts from Panicum maximum

“…As shown in Table I Chloroplasts of the upper and lower bands of the Ludox gradient were tested for intactness and distribution of RuDPCase. MC chloroplasts are expected to contain GPDH approximately equivalent to BSC chloroplasts while RuDPCase should be restricted to the BSC chloroplasts (15). As shown in Table I, MC chloroplasts isolated from protoplasts or from Ludox gradients contained no measurable RuDPCase activity but did show greater than a 10-fold increase in GPDH activity after lysis.…”