Photosystem II oxygen evolution capacity the steady-state level of photosyst II (PSII) reaction center polypeptide DI and its transcript and template levels in Zea mays L (Xinyu No.4) under waler stress and rewatering were studied. The results indicated that PSII and whole chain electron transport capacities decreased slightly under moderate water stress and appreciably under severe water stress and could not recover to control level upon rewatering the resuts of western and northem blots showed that the content of PSII reaction center polypeptide DI changed as a similar pattern to PSII and whole-chain electron transport capacitiesz. Dot blot analysis for DNA showed that there was no obvious response of the template level of Dl to water stress or rewatering. From the results, it was concluded that PSII was the major site affected by water stress, where the functional, loss of PaII could be attributed to the reducion-center polypeptide D1, which may be caused by the decrease in its transcript Ievel. Rewatefing codid only ameliorate slightly under moderate water stress but coutd not recover to control Level under severe water stress.