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. 1992 Oct;100(2):939–946. doi: 10.1104/pp.100.2.939

Degree of C4 Photosynthesis in C4 and C3-C4Flaveria Species and Their Hybrids 1

I. CO2 Assimilation and Metabolism and Activities of Phosphoenolpyruvate Carboxylase and NADP-Malic Enzyme

George T Byrd 1,2,3, R Harold Brown 1,2,3, Joseph H Bouton 1,2,3, Carole L Bassett 1,2,3, Clanton C Black 1,2,3
PMCID: PMC1075647  PMID: 16653079

Abstract

The degree of C4 photosynthesis was assessed in four hybrids among C4, C4-like, and C3-C4 species in the genus Flaveria using 14C labeling, CO2 exchange, 13C discrimination, and C4 enzyme activities. The hybrids incorporated from 57 to 88% of the 14C assimilated in a 10-s exposure into C4 acids compared with 26% for the C3-C4 species Flaveria linearis, 91% for the C4 species Flaveria trinervia, and 87% for the C4-like Flaveria brownii. Those plants with high percentages of 14C initially fixed into C4 acids also metabolized the C4 acids quickly, and the percentage of 14C in 3-phosphoglyceric acid plus sugar phosphates increased for at least a 30-s exposure to 12CO2. This indicated a high degree of coordination between the carbon accumulation and reduction phases of the C4 and C3 cycles. Synthesis and metabolism of C4 acids by the species and their hybrids were highly and linearly correlated with discrimination against 13C. The relationship of 13C discrimination or 14C metabolism to O2 inhibition of photosynthesis was curvilinear, changing more rapidly at C4-like values of 14C metabolism and 13C discrimination. Incorporation of initial 14C into C4 acids showed a biphasic increase with increased activities of phosphoenolpyruvate carboxylase and NADP-malic enzyme (steep at low activities), but turnover of C4 acids was linearly related to NADP-malic enzyme activity. Several other traits were closely related to the in vitro activity of NADP-malic enzyme but not phosphoenolpyruvate carboxylase. The data indicate that the hybrids have variable degrees of C4 photosynthesis but that the carbon accumulation and reduction portions of the C4 and C3 cycles are well coordinated.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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