Effects of continuously or discontinuously low temperature and poor light on photosynthesis in pepper leaves

The effects of continuously low temperature(15℃/15℃,5℃/5℃,day/night)or discontin- uously low temperature(15℃/5℃,day/night)and poor light(100μmol/(m~2.s),12 h photoperiod)on photosynthesis in pepper leaves treated under controlled conditions for 15 d were investigated,using CO_2 exchange and chlorophyll fluorescence parameters.The results showed that in 15℃/5℃,and 5℃/5℃treated pepper leaves,F_o increased,and F_m,F_v/F_m decreased,greater in 5℃/5℃treated ones than in 15℃/5℃treated ones,indicating that damages occurred in PSⅡreaction centers of pepper leaves,and more severely in 5℃/5℃treated ones than in 15℃/5℃treated ones.15℃/15℃treatment had little effect on F_o,F_m and F_v/F_m in pepper leaves,suggesting that no damage occurred.TheΦPSⅡ,F′_v/F′_m and chlorophyll contents in all pepper leaves treated by low temperature and poor light decreased,and the lower the temperature,the greater the decrease.Net photosynthetic rate and photosynthetic capacity decreased in 15℃/15℃treated pepper leaves,and that could not be detected in 15℃/5℃and 5℃/5℃treated ones.Membrane permeability and MDA content in 15℃/5℃treated pepper leaves increased remarkably, but that in 15℃/15℃and 15℃/5℃treated ones increased indistinctively.