High Light-Induced Unstacking of Thylakoids and Randomization of Pigment-Protein Complexes of Chloroplast

Using absorbance changes at 540 nm and the per cent chlorophyll in 10K pellet after digitonin fractionation as the criteria of thylakoid stacking, high light induced unstacking of thylakoids and randomization of pigment protein complexes of chloroplast was characterized. Cation-induced increase in absorbance at 540 nm was abolished when chloroplasts were exposed to high light. Also, the high light induced decrease in absorbance at 540 nm was more pronounced in low salt chloroplasts as compared to the decrease in 540 nm absorbance in chloroplasts isolated in high salt. The decrease in the fraction of chlorophyll in digitonin fractionated 10K pellet was much more than the decrease in chlorophyll in 10K pellet from high salt chloroplasts exposed to high light. These results suggest that high light causes unstacking of thylakoids.