Leaf C3 Photosynthesis in silico: Integrated Carbon/Nitrogen Metabolism

Abstract

Acomputermodel of C3 photosynthesis comprising light reactions, electron-proton transport, enzymatic reactions and regulatory functions is presented as a system of differential budget equations for interme- diate compounds. Carbon and nitrite reduction systems are linked assuming that nitrite reduction is the dominant proton-coupled alternative electron transport pathway compensating for ATP consumption by starch synthesis and other non-photosynthetic processes. The principal theoretical hypothesis is that the carbon skeletons for the freshly synthesized amino acids are partitioned fromthe pool of phosphoglyceric acid (PGA) before its reduction in photosynthesis. Consequently, the rate of nitrite reduction is controlled by ferredoxin reduction and PGA levels. The latter simultaneously controls the rate of starch synthesis – themajor alternativeATP consumer linking nitrite reductionwith starch synthesis. Themodel reproduces light and CO2 response curves of photosynthesis, chlorophyll fluorescence and 810nm transmittance signals during steady state, as well as during induction and oscillations. The model explains the integral Nitrogen/Carbon (N/C) ratios of plant tissues and predicts that the availability of nitrogen may limit the photosynthetic rate in natural communities.