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 C4 or C3 pathway

Raghavendra, Agepati S. (1980) 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 C4 or C3 pathway Physiologia Plantarum, 49 (4). pp. 405-409. ISSN 0031-9317

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Official URL: http://onlinelibrary.wiley.com/doi/10.1111/j.1399-...

Related URL: http://dx.doi.org/10.1111/j.1399-3054.1980.tb03325.x

Abstract

The pattern of photosynthetic carbon fixation by leaves of Amaranthus paniculatus L. (a C4 plant) and Oryza sativa L. (a C3 plant) varied with age. Younger leaves of A. paniculatus incorporated 14CO2 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 C4 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 C4 or C3. The high rate of 14CO2 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 CO2 directly to RuBP carboxylase in the bundle sheath.

Item Type:Article
Source:Copyright of this article belongs to John Wiley and Sons.
Keywords:Amaranthus; C3; C4 Photosynthesis; Oryza; Leaf Age; Primary Carboxylation Variation
ID Code:40248
Deposited On:23 May 2011 08:54
Last Modified:23 May 2011 08:54

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