Km (CO2) values of ribulose-1,5-bisphosphate carboxylase in grasses of different C4 type |
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Authors: | Paul Hattersley |
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Affiliation: | 1. Department of Botany, National University of Singapore, Kent Ridge, Singapore 0511;2. Taxonomy Unit, Research School of Biological Sciences, Australian National University, Canberra, A.C.T. 2601, Australia |
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Abstract: | Statistical analysis of Km (CO2) values of ribulose-1,5-bisphosphate (RuBP) carboxylase from 35 C4 grass species shows that the mean value for PEP-carboxykinase (PCK) type C4 species (41.4±s.e. 2.2 μM CO2) is significantly different from that of NAD-malic enzyme (NAD-ME) type species (55.3±3.1 μM CO2) or NADP-malic enzyme (NADP-ME type species (52.5±s.e. 2.0μM CO2). These C4 type differences remain detectable within both the eu-panicoid and chloridoid grass subfamilies. By contrast, no between-subfamily differences were found within C4 types. Variation in Km (CO2) values of RuBP carboxylase may be related to in vivo differences in CO2 concentration at the enzyme site, mediated perhaps by differences in CO2-leakiness of C4 leaf ‘photosynthetic carbon reduction’ (PCR or ‘Kranz’) tissue. |
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Keywords: | Grasses Gramineae ribulose-1,5-bisphosphate carboxylase photosynthesis systematics. |
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