Electron and proton transfer in chloroplasts in silico. 2.Effect of diffusion restrictions on photosynthetic processes in spatially heterogenous thylakoids

In the present work, we theoretically studied the impact of diffusion limitations that determine the degree of lateral mobility of protons and the mobile electronic carriers (plastoquinone, plastocyanin), on the kinetics of photoinduced changes in pHi in the metabolic state 3 (conditions of intensive synthesis of ATP) and 4 (the state of photosynthetic control). Numerical experiments have been conducted using our previously developed mathematical model of photosynthetic electron and proton transport in chloroplasts, taking into account the non-uniform distribution of the electron-transport and ATP-synthase complexes in thylakoid membranes of granal and stromal thylakoids. The kinetics of interthylakoid pHi variations and lateral profiles of mobile electron carriers concentrations in granal and intergranal thylakoids were studied. The model predicts the establishment of non-uniform lateral profiles of pHi under the conditions of intensive ATP synthesis, when the acidification of the lumen in the centre of grana occurs considerably slower than inside the stromal thylakoids. The variation of the diffusion coefficients of protons inside the thylakoids and the mobile electron carriers may result in a significant impact on the lateral profiles of pHi and the redox state of the mobile electron carriers.