Control of phosphate turnover as a rate-limiting factor and possible cause of oscillations in photosynthesis: a mathematical model

Abstract

A mathematical model of photosynthetic processes, comprising the primary reactions, the carbon reduction cycle, the phosphate translocator and sucrose synthesis, has been constructed and solved by computer. The aim was to simulate oscillations in photosynthesis generated by changes in CO2concentration and light intensity. The activation of sucrose synthesis by organic phosphates and its inactivation by orthophosphate was taken into account. Slowly dampening oscillations could be generated only if modulation of sucrose synthesis was assumed to proceed with a time-lag of about 15–20 s. It is concluded that the rate of phosphate turnover, as determined by the activity of sucrose synthesis, may be a limiting factor in determining the maximum rate of photosynthesis in saturating CO2concentrations and photon flux densities. The model demonstrates an absolute need for a lag in the feedback loop controlling the rate of photosynthesis if oscillations are to be generated. It also accommodates the possibility that the rate of photosynthesis may be controlled by accumulating sucrose, through modulation of the activity of the sucrose synthesizing system.