Abstract
Light and heat stresses induce damage to Photosystem II (PSII). We investigated relationship between the stress-induced damage to the D1 protein and unstacking of spinach thylakoids. For efficient migration of the damaged PSII complexes from the grana to the stroma thylakoids where the damaged PSII is repaired, the grana should become unstacked. We used digitonin fractionation method to estimate membrane unstacking. During strong illumination light intensity 1,000 μmol photons m-2 s-1 of PSII at 25degree, the thylakoids became markedly unstacked. Heat stress (40 degree) in the dark also induced thylakoid unstacking. Interestingly, the extent of D1 degradation was proportional to the rate of the thylakoid unstacking. By contrast, the thylakoid unstacking did not take place at 4 degree under high light and the D1 degradation was prevented. These results suggest that the thylakoid unstacking is necessary for efficient degradation of the damaged D1 protein.
