Abstract
The thermal dissipation of excess light energy requires a pH gradient (ΔpH) across the thylakoid membranes. There are two alternative pathways to form this ΔpH; the cyclic electron flow around PSI (CEF-PSI) and the water-water cycle (WWC). Although the thermal dissipation was enhanced when photosynthesis was suppressed by low-temperature, it is unclear which pathway is mainly driven to form ΔpH.
When rice plants were treated at low-temperature (20oC) during short-term (sec to min) or long-term (day to week) periods, CO2 assimilation rate decreased and NPQ increased. The short-term low-temperature led to a decrease in the ratio of electron transport rate in WWC to PSII (Ja/Jf) and an increase in the ratio of the quantum efficiency in PSI to PSII (ΦPSI/ΦPSII). However, the long-term low-temperature enhanced Ja/Jf and reduced ΦPSI/ΦPSII. Thus, CEF-PSI was driven at short-term low-temperature and WWC was induced during long-term low-temperature.
