Mathematical modelling of photoinhibition and Photosystem II repair cycle. I. Photoinhibition and D1 protein degradation in vitro and in the absence of chloroplast protein synthesis in vivo.

The kinetics of photoinhibition of Photosystem II and D1 protein degradation were studied by applying mathematical modelling to new and published data. The word 'photoinhibition' refers here only to such inhibition of PS II activity that requires chloroplast protein synthesis for recovery. It is shown that acceptor-side photoinhibition in vitro as well as in vivo photoinhibition in higher plants and cyanobacteria in the presence of prokaryotic translation inhibitors follow first-order kinetics. Degradation of damaged D1 protein also fits in a first-order reaction equation with respect to the concentration of photoinhibited PS II centres. It is shown that photoprotective lowering of the ratio of variable to maximum fluorescence can be distinguished from the lowering of this ratio associated with photoinhibition.