The influence of sugar synthesis and transport rates on bioenergetics and kinetics of higher plant photosynthesis

We have obtained the theoretical dependences of stromal metabolite steady-state concentrations on external inorganic phosphate (Pi) concentration. For this purpose, the theoretical model of photosynthesis, earlier described in [Ann. Appl. Biol. 138 (2001) 117], was modified to account for the regulation of starch formation by 3-phosphoglycerate (PGA) to Pi ratio. When the rate constant of starch synthesis is taken to be independent on PGA/Pi ratio, the steady-state concentrations of Calvin cycle metabolites and starch were found to change insignificantly as external Pi concentration increases in wide range. However, as external Pi range exceeds a critical value, the steady-state concentrations of all metabolites change abruptly. If the rate constant of starch synthesis depends on PGA/Pi ratio, the steady-state concentrations of stromal metabolites change qualitatively in the same way with the increase of external Pi. However, no abrupt changes of metabolite and starch steady-state levels at high concentration of Pi are observed. These results testify that the control of starch synthesis by PGA/Pi ratio makes the photosynthetic system more stable in wide range of external Pi concentrations.