Inorganic carbon uptake during photosynthesis. II. Uptake by isolated Asparagus mesophyll cells during isotopic disequilibrium. [Asparagus sprengeri]

Journal Article · Tue Apr 01 04:00:00 EST 1986 · Plant Physiol.; (United States)

OSTI ID:7024324

Espie, G S; Owttrim, G W; Colman, B

The species of inorganic carbon (CO/sub 2/ or HCO/sub 3//sup -/) taken up as a source of substrate for photosynthetic fixation by isolated Asparagus sprengeri mesophyll cells is investigated. Discrimination between CO/sub 2/ or HCO/sub 3//sup -/ transport, during steady state photosynthesis, is achieved by monitoring the changes (by /sup 14/C fixation) which occur in the specific activity of the intracellular pool of inorganic carbon when the inorganic carbon present in the suspending medium is in a state of isotopic disequilibrium. Quantitative comparisons between theoretical (CO/sub 2/ or HCO/sub 3//sup -/ transport) and experimental time-courses of /sup 14/C incorporation, over the pH range of 5.2 to 7.5, indicate that the specific activity of extracellular CO/sub 2/, rather than HCO/sub 3//sup -/, is the appropriate predictor of the intracellular specific activity. It is concluded, therefore, that CO/sub 2/ is the major source of exogenous inorganic carbon taken up by Asparagus cells. However, at high pH (8.5), a component of net DIC uptake may be attributable to HCO/sub 3//sup -/ transport, as the incorporation of /sup 14/C during isotopic disequilibrium exceeds the maximum possible incorporation predicted on the basis of CO/sub 2/ uptake alone. The contribution of HCO/sub 3//sup -/ to net inorganic carbon uptake (pH 8.5) is variable, ranging from 5 to 16%, but is independent of the extracellular HCO/sub 3//sup -/ concentration. The evidence for direct HCO/sub 3//sup -/ transport is subject to alternative explanations and must, therefore, be regarded as equivocal. Nonlinear regression analysis of the rate of /sup 14/C incorporation as a function of time indicates the presence of a small extracellular resistance to the diffusion of CO/sub 2/, which is partially alleviated by a high extracellular concentration of HCO/sub 3//sup -/.

• Research Organization: York Univ., Downsview, Ontario
• OSTI ID: 7024324
• Journal Information: Plant Physiol.; (United States), Journal Name: Plant Physiol.; (United States) Vol. 80:4; ISSN PLPHA
• Country of Publication: United States
• Language: English

Related Subjects

550501* -- Metabolism-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
CARBON 14 COMPOUNDS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON DIOXIDE FIXATION
CARBON OXIDES
CARBONIC ACID
CHALCOGENIDES
CHEMICAL REACTIONS
HYDROGEN COMPOUNDS
INORGANIC ACIDS
ISOTOPE APPLICATIONS
LABELLED COMPOUNDS
MATHEMATICS
MEASURING METHODS
OXIDES
OXYGEN COMPOUNDS
PH VALUE
PHOTOCHEMICAL REACTIONS
PHOTOSYNTHESIS
PLANT CELLS
REGRESSION ANALYSIS
SOLUTES
STATISTICS
SYNTHESIS
TRACER TECHNIQUES
UPTAKE