Plant sample integrity is important for efficient photosystem II repair and thylakoid remodelling in Arabidopsis.

The thylakoid is a dynamic membrane that houses the protein complexes involved in the light-dependent reactions of photosynthesis. Although light provides the energy that drives these reactions, it also damages the photosynthetic apparatus, particularly photosystem II. This damage can be repaired via the photosystem II repair cycle, a process thought to be accompanied by structural rearrangements of the thylakoid membrane. When the light-induced damage exceeds the capacity for repair, photoinhibition occurs, resulting in a decline in photosynthetic capacity. While photoinhibition has been extensively studied using various leaf sample preparations, the effects of sample preparation on photoinhibition and thylakoid structural rearrangements remain largely unknown. Here, we investigated the effects of high-light treatment on photoinhibition and thylakoid architecture across several leaf sample preparations. By analysing the quantum yield of photosystem II and electron transport from photosystem II to photosystem I, we found that the severity of photoinhibition differed between leaf sample preparations exposed to identical high-light conditions. Our results show that excised leaf material accumulates more damage to photosystem II than intact plant material, likely due to impaired photosystem II repair in excised leaf material. Using electron microscopy, we observed changes in the thylakoid architecture after high-light treatment in intact plant material, whereas these changes were absent in excised leaf material. This suggests that thylakoid structural reorganisations may contribute to efficient photosystem II repair. Taken together, our results indicate that leaf sample preparation influences both photosystem II repair and thylakoid structural reorganisations in response to high light.