Photosynthesis, photoinhibition, and antioxidant system in tomato leaves stressed by low night temperature and their subsequent recovery.

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. Crown