A nuclear mutant of Arabidopsis thaliana selected for enhanced sensitivity to light-chill stress is altered in PSII electron transport activity

Chilling in the light imposes a considerable level of stress on the photosynthetic apparatus, resulting in a decrease of photosystem II activity and the quenching of maximum and variable florescence, We selected in a fah-1 mutagenized population of Arabidopsis thaliana, which permits a direct visible evaluation of the intensity of chlorophyll (Chl) fluorescence, a monogenic recessive nuclear mutant hypersensitive to photoinhibition induced bg light and cold, The major phenotypic trait of the mutant is the appearance of chlorotic areas on developed leaves, Photochemical analyses indicate that the mutant is hypersensitive to photoinhibition in excess light in the cold but also at room temperature. The susceptibility to photoinhibition is a consequence of perturbations in photochemistry already present in unstressed plants, Such perturbations result in a greater fraction of the primary acceptor Q(A) remaining in the reduced state even at low light fluxes, From estimates of the number of total and functional PSII units and measurements of PSII quantum yield and Q(A)(-) reoxidation kinetics, the basic lesion of the mutant seems restricted to PSII photochemistry likely affecting the rate of electron transport from Q(A)(-) to Q(B).