We studied the photooxidative effects of methyl viologen (MV) on PSII in rice (Oryza sativa L.). Leaves were held at either room temperature (RT) or 4$^{circ}C$. In the presence of MV, the photochemical efficiency of PSII, or $F_{v/}$ $F_{m}$, was more depressed at RT than at the low temperature (LT), but the loss of D1 protein that was detected at RT was not observed at LT. However, the decline in the content of functional PSII, 1/ $F_{o}$ - 1/ $F_{m}$, was similar for My-treated leaves at either temperature. These results suggest that, at LT, PSII is not protected from MV-induced photooxidation, although degradation of the D1 protein is delayed. The 1/ $F_{o}$ - 1/ $F_{m}$ decreased by MV treatment at RT was significantly recovered during dark incubation for 2 h. Recovery of a small portion of 1/ $F_{o}$ - 1/ $F_{m}$ was also possible, even for tissues treated with MV at LT. Therefore, we believe that MV-induced reversible photoinactivation may exist. This possibility is further discussed in terms of changes in the de-epoxidation state and the rate of PSII-driven electron transport.sport.t.sport.t.