Abstract:Chilling (1 ℃ or 5℃, 16 h) treatment inhibited PSⅡ but not PSⅠ of photosynthesis in cucumber, a chilling sensitive plant. Oxygen evolution, variable fluorescence, and DCIP photoreduction were inhibited significantly, and the latter two could be recovered to the control level by adding artificial electron donors. These results suggest that chilling temperature damages PSⅡ of cucumber only on the oxidizing side and does not affect its reaction center.