Abstract
The magnitude and extent of Crassulacean acid metabolism (CAM) activity in two Clusia species was manipulated to investigate the regulation of the distinct CAM phases. First, in response to leaf-air vapor pressure deficit at night, changes in leaf conductance altered on-line carbon-isotope discrimination throughout the theoretical range for dark CO2 uptake during CAM. These ranged from the limit set by phosphoenolpyruvate carboxylase (PEPc) (-6[per mille (thousand) sign], [delta]13C equivalent of -2[per mille (thousand) sign]) to that imposed by diffusion limitation (+4[per mille (thousand) sign], [delta]13C equivalent of -12[per mille (thousand) sign]), but the lowest carbon-isotope discrimination occurred when P[square root]pa was only 0.7. Second, when the availability of external or internal sources of CO2 was reduced for both field- and greenhouse-grown plants, CO2 uptake by day via PEPc during phase II largely compensated. Third, by reducing the dark period, plants accumulated low levels of acidity, and CO2 uptake occurred throughout the subsequent light period. Discrimination switched from being dominated by PEPc (phase II) to ribulose 1,5-bisphosphate carboxylase/oxygenase (phase III), with both enzymes active during phase IV. Under natural conditions, photochemical stability is maintained by extended PEPc activity in phase II, which enhances acid accumulation and delays decarboxylation until temperature and light stress are maximal at midday.
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Selected References
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- Bowman W. D., Hubick K. T., von Caemmerer S., Farquhar G. D. Short-term changes in leaf carbon isotope discrimination in salt- and water-stressed c(4) grasses. Plant Physiol. 1989 May;90(1):162–166. doi: 10.1104/pp.90.1.162. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Holtum J. A., O'leary M. H., Osmond C. B. Effect of Varying CO(2) Partial Pressure on Photosynthesis and on Carbon Isotope Composition of Carbon-4 of Malate from the Crassulacean Acid Metabolism Plant Kalanchoë daigremontiana Hamet et Perr. Plant Physiol. 1983 Mar;71(3):602–609. doi: 10.1104/pp.71.3.602. [DOI] [PMC free article] [PubMed] [Google Scholar]
- Morison J. I., Gifford R. M. Stomatal sensitivity to carbon dioxide and humidity: a comparison of two c(3) and two c(4) grass species. Plant Physiol. 1983 Apr;71(4):789–796. doi: 10.1104/pp.71.4.789. [DOI] [PMC free article] [PubMed] [Google Scholar]