Downregulation of PSII activity and increased cyclic electron transport in cotton prevents PSI from photoinhibition due to night chilling

The objective of this experiment was to study the effects of night chilling on the photosynthetic characteristics of cotton (Gossypium hirsutum L.) at a boll-forming stage. The results suggest that overreduction of PSII after night chilling (≤ 10°C) led to excess excitation energy in cotton leaves. The night chilling (compared to 22°C) reduced PSI acceptor side limitation under moderate and high light intensity and increased maximum photooxidizable P700. This suggests that in contrast to PSII, PSI was protected from photoinhibition due to night chilling. However, PSII activity and linear electron transport were not significantly affected by the 30/16°C treatment. In addition, the night chilling (≤ 10°C) increased the quantum yield of cyclic electron transport. This suggests that cyclic electron transport around PSI might be important to prevent photoinhibition of PSI and PSII in cotton under night chilling stress.