The effects of low night temperature (LNT, i.e., 9 and 6 ◦C) stress and rewarming (15 ◦C night temperature)
on the photosynthesis, photosystems I and II (PSI and PSII), and antioxidant system of tomato leaves
were studied. The results showed that 9 d of LNT treatment led to an irreversible reduction in the photosynthetic
rate. This reduction was accompanied by stomatal limitation of CO2 supply and significant
decline in ribulose-1,5-bisphosphate carboxylase/oxygenase activity at the transcription level, as well
as sucrose accumulation. LNT treatment induced the reversible photoinhibition of PSII, decreased PSII
activity, increased the photochemical yield of PSI Y(I), and markedly caused the acceptor side limitation
of PSI. This finding was reflected by the higher value of Y(NA) in the treated plants than in the control. At
the same time, a downregulation of electron transport for photosynthetic carbon reduction under LNT
was mostly compensated by Ja(O2-dependent) driven by the water–water cycle.