Controlled distribution of electrons between acceptors in chloroplasts: a theoretical consideration

The coupled processes of electron distribution in chloroplasts in the light are quantitatively analyzed by means of a steady-state model. The equation s for electron transport to ferredoxin, nitrite reduction, cyclic electron transport, malate valve, 3-phosphoglycerate reduction, and O-2 reduction ar e developed. Kinetic parameters are derived from known data. Using the kine tic properties of the system and the known metabolite concentrations, the m odel demonstrates that photosynthetically generated electrons can be used e fficiently in photosynthesis. It is shown that the modelled system can main tain the NADPH/NADP(+) ratio constant within a wide range of light intensit ies. The control coefficients for different electron fluxes have been calcu lated. The calculated sum of control coefficients is significantly below un ity, a fact that can be explained by the existence of conserved moieties in this system. The possible role of the electron distribution in leaf cells under normal conditions and during stress is discussed. (C) 1999 Elsevier S cience B.V. All rights reserved.