Effects of water stress on major photosystem II gene expression and protein metabolism in barley leaves

Although it has long been recognized that water deficit in plants reduces photosystem (PS) II mRNAs and proteins, the detailed mechanisms behind this have not been thoroughly elucidated. In the present study, effects of water stress in barley leaves on degradation of major PSII mRNA and dissociation and migration of PSII proteins were investigated. The results indicated that (1) the steady-state levels of major PSII mRNAs and proteins declined with increasing water stress, as a consequence of increased degradation; under severe water stress, the half-lives of D1 and D2 proteins decreased from 12-14 h to 7-8 h and the half-lives of psbA and psbD mRNA decreased from above 16 to 6-10 h; (2) monomerization of PSII were increased during water stress. Severe water stress accelerated turnover of PSII and inhibited PSII activities.