MODELING C3-PHOTOSYNTHESIS - A SENSITIVITY ANALYSIS OF THE PHOTOSYNTHETIC CARBON-REDUCTION CYCLE

A model of the C3 photosynthetic system is developed which describes t he sensitivity of the steady-state rate of carbon dioxide assimilation to changes in the activity of several enzymes of the system. The mode l requires measurements of the steady-state rate of carbon dioxide ass imilation, the concentrations of several intermediates in the photosyn thetic system, and the concentration of the active site of ribulose 1, 5-bisphosphate carboxyalse/oxygenase (Rubisco). It is shown that in su nflowers (Helianthus annuus L.) at photon flux densities that are larg ely saturating for the rate of photosynthesis, the steady-stete rate o f carbon dioxide assimilation is most sensitive to Rubisco activity an d, to a lesser degree, to the activities of the stromal fructose 6-bis phosphatase and the enzymes catalysing sucrose synthesis. The activiti es of sedoheptulose 1,7-bisphosphatase, ribulose 5-phosphate kinase, A TP synthase and the ADP-glucose pyrophosphorylase are calculated to ha ve a negligible effect on the flux under the high-light conditions. Th e utility of this analysis in developing simpler models of photosynthe sis is also discussed.