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

Abstract

The coupled processes of electron distribution in chloroplasts in the light are quantitatively analyzed by means of a steady-state model. The equations for electron transport to ferredoxin, nitrite reduction, cyclic electron transport, malate valve, 3-phosphoglycerate reduction, and O-2 reduction are developed. Kinetic parameters are derived from known data. Using the kinetic properties of the system and the known metabolite concentrations, the model demonstrates that photosynthetically generated electrons can be used efficiently in photosynthesis. It is shown that the modelled system can maintain the NADPH/NADP(+) ratio constant within a wide range of light intensities. The control coefficients for different electron fluxes have been calculated. The calculated sum of control coefficients is significantly below unity, 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 Science B.V. All rights reserved.