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Variation with age in the photosynthetic carbon fixation pattern by leaves of Amaranthus paniculatus and Oryza sativa: Change in the primary carboxylation but no shift from C 4 or C 3 pathway
Author(s) -
RAGHAVENDRA AGEPATI S.
Publication year - 1980
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1980.tb03325.x
Subject(s) - photosynthesis , oryza sativa , c4 photosynthesis , carbon fixation , sugar phosphates , phosphoenolpyruvate carboxylase , carboxylation , ribulose , botany , rubisco , biology , pyruvate carboxylase , vascular bundle , sugar , malic acid , phosphoenolpyruvate carboxykinase , chemistry , biochemistry , phosphate , enzyme , citric acid , gene , catalysis
The pattern of photosynthetic carbon fixation by leaves of Amaranthus paniculatus L. (a C 4 plant) and Oryza sativa L. (a C 3 plant) varied with age. Younger leaves of A. paniculatus incorporated 14 CO 2 into malate and aspartate while senescent leaves fixed predominantly into phosphoglycerate (PGA) and sugar phosphates. Only developing leaves of O. sativa formed malate/aspartate whereas mature and senescent leaves produced PGA/sugar phosphates as the initial labelled products. Correspondingly the ratio of phosphoenolpyruvate/ribulose bisphosphate (RuBP) carboxylase activities was higher in younger leaves of A. paniculatus and developing leaves of O. sativa than in older leaves. However, pulse chase experiments revealed that the main donors of carbon to end products, irrespective of leaf stage, were C 4 acids and PGA in A. paniculatus and O. sativa respectively. The results suggest that although an apparent change from initial β‐carboxylation to RuBP carboxylation occurs during leaf ontogeny in both the plants, the overall leaf photosynthesis remains C 4 or C 3 . The high rate of 14 CO 2 incorporation into PGA/sugar phosphates by senescent leaves of A. paniculatus is suggested to be partly due to the increased intercellular spaces in their mesophyll, allowing greater access of CO 2 directly to RuBP carboxylase in the bundle sheath.