Stoichiometry of photorespiration during C3-photosynthesis is not fixed: evidence from combined physical and stereochemical methods
The stoichiometry of photorespiration, S, is defined as the fraction of glycolate carbon photorespired. It is postulated that under steady-state conditions there are two determinants of the ratio of photorespiration to net photosynthesis: the partitioning of ribulose bisphosphate between oxidation and carboxylation, and the partitioning of glycolate between reactions leading to complete oxidation to CO/sub 2/ (S . 100%) and those yielding CO/sub 2/ plus serine (S . 25%). S may be calculated using two independent probes of the system. The physical probe, using an infrared gas analyzer, measured photorespiration and net photosynthesis, and hence their ratio PR/NPS . pn(phys). The metabolic probe employed tracer (3R)-D-(3-/sup 3/H1,3-/sup 14/C)glyceric acid to determine r, the fraction of /sup 3/H retained in the triose phosphates leaving the chloroplasts. It is deduced from the postulated model that S . pn(phys) . r/(1 - r). Experiments have been performed with illuminated tobacco leaf discs (inverted) under varying concentrations of O/sub 2/ and CO/sub 2/. Increasing O/sub 2/ at constant CO/sub 2/ increased pn(phys) and decreased r, whereas increasing CO/sub 2/ at constant O/sub 2/ had the opposite effect. S more than doubled at 32 degrees C on going from 16 to 40% O/sub 2/ (340 microliters CO/sub 2//liter) and decreased 40% on going from 200 to 700 microliters CO/sub 2//liter (21% O/sub 2/). For discs in normal air S was somewhat greater than 27%. It is suggested that net photosynthesis, and therefore crop yields, could be increased by selecting for crop plants with reduced photorespiration stoichiometry.
- Research Organization:
- Connecticut Agricultural Experiment Station, New Haven
- OSTI ID:
- 5665908
- Journal Information:
- Arch. Biochem. Biophys.; (United States), Vol. 237:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
PHOTOSYNTHESIS
MEASURING METHODS
RESPIRATION
STOICHIOMETRY
CARBON 14 COMPOUNDS
CARBON DIOXIDE
METABOLISM
NICOTIANA
OXYGEN
TRACER TECHNIQUES
TRITIUM COMPOUNDS
CARBON COMPOUNDS
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
ELEMENTS
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
NONMETALS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PLANTS
SYNTHESIS
550501* - Metabolism- Tracer Techniques