The combination of drought and high light poses a challenge for plant functions. We compared the effect of prolonged drought on desert and Mediterranean ecotypes of wild barley (Hordeum spontaneum L. Koch). Relative water content in leaves of drought treated plants decreased significantly as compared to the control plants. This reduction was accompanied by almost complete inhibition of net CO2 assimilation. Photochemical activity of PSII under high light and drought conditions decreased in the Mediterranean ecotype as compare to the control treatment; surprisingly, we detected an increase of PSII activity under high light in the desert ecotype as compared to the control irrigated plants. In addition total anthocyanin content increased in leaves of desert ecotype under drought by more than two folds as compared to the control plants. The nature of photochemical activity under high light was further examined under low oxygen concentrations (2%), which inhibit photorespiration and other oxygen dependent processes such as the water-water cycle. We have found that low oxygen eliminated the increase of PSII activity in the drought treated desert ecotype. In conclusion we have found that desert ecotypes of wild barely confronts drought stress and high light by O2 dependent increase of photochemical activity, which is accompanied , and by a large increase of anthocyanin. These results suggest an important role for photorespiration and other oxygen related mechanisms, in the adaptation of C3 plants to desert environment.