In conclusion, the lower chilling–light tolerance of photosystems
in young cucumber leaves was due to: 1, the higher sensitivity
of PSI to ROS; and 2, the higher PSII excitation pressure caused
by the severer PSI photoinhibition in young leaves. But it was independent
of the ROS content, the sensitivity of PSII to excitation
pressure and the development of photosystem function and carbon
assimilation capacity.