Different response of photosystem II to short and long-term drought stress in Arabidopsis thaliana.

Short- and long-term drought stress on photosystem II (PSII) and oxidative stress were studied in Arabidopsis thaliana. Under drought stress, chlorophyll (Chl) content, Chl fluorescence, relative water content and oxygen evolution capacity gradually decreased, and the thylakoid structure was gradually damaged. Short-term drought stress caused a rapid disassembly of the light-harvesting complex II (LHCII). However, PSII dimers kept stable under the short-term drought stress and significantly decreased only after 15 days of drought stress. Immunoblotting analysis of the thylakoid membrane proteins showed that most of the photosystem proteins decreased after the stress, especially for Lhcb5, Lhcb6 and PsbQ proteins. However, surprisingly, PsbS significantly increased after the long-term drought stress, which is consistent with the substantially increased non-photochemical quenching (NPQ) after the stress. Our results suggest that the PSII-LHCII supercomplexes and LHCII assemblies play an important role in preventing photo-damages to PSII under drought stress.