Abstract
The leaves of rice seedlings show severe visible injury after a few days chilling (10 °C) only when the roots were not chilled and kept at 25 °C (L/H), whereas no such injury is observed when the whole seedlings were chilled at 10 °C (L/L). This High-Root-Temperature-induced (HRT) chilling injury is preceded by the malfunction of photosynthetic election transport between PSII and PSI, and cyclic electron transport of PSI. In order to help elucidate the mechanism of the HRT chilling injury, in this study, photosynthesis analyses were performed in the third leaves of rice seedlings at 10 °C during the dark chilling treatments. In the L/H leaves, PSII lost the ability to transfer electrons from QA and QB independently of light. Light did not induce electron transport from PSII to PSI, cyclic electron transport of PSI, ΔpH across thylakoid membrane, or light-dependent increase in zeaxanthin concentration in the L/H leaves, although they were induced in the L/L leaves. Thus, the electron transfer from QA to QB was blocked as the first event of HRT-chilling injury, and the consequent malfunction of thermal dissipation seems to cause the visible injury under light.
