Previous studies showed that PSI photoinhibition under
chilling–light treatment is mainly due to over-accumulation of
ROS induced by the inhibition of thylakoid-bound APX and SOD
under chilling–light [43–45]. However, in this study, we observed
that the ROS contents in the young and the function leaves were
similar (Fig. 4), which indicates that the difference of PSI chilling
tolerance between young and function leaves was due to the different
sensitivity of PSI to ROS rather than the ROS content in leaves.