Responses of photosynthesis and phosphorylation of the light-harvesting complex of photosystem II to chilling temperature in ecologically divergents cultivars of rice

Rice (Oryza sativa L.). which is susceptible to chilling damage, is cultivated in diverse environments ranging from tropical to temperate regions. In the present study photosynthetic responses to long-term chilling were evaluated for five rice cultivars differing in their ecological origins. Furthermore, the hypothesis was tested that when chilled over several days, rice adapted to temperate climates may maintain a greater capacity for phosphorylation of the light-harvesting protein complex of PSII (LHCII) than rice bred for tropical environments. Seedlings were grown at 28/22 degrees C day/night temperature and PPFD of 550 micromol m(-2) s(-1) until the third leaf was fully expanded, at which time they were transferred to 10/8 degrees C day/night temperature under the same light intensity for 6 d, followed by recovery at 18/15 degrees C and 25/21 degrees C, for 1 and 2 d, respectively. Leaf photosynthesis decreased by 40-89% within 3 d after transfer to 10/8 degrees C for the cultivars studied, with significant differences developing within 2 d. Photochemical efficiency of PSII, measured by F(v) F(m), followed a similar trend. After rewarming plants, photosynthesis and photochemistry fully recovered in two temperate Japonica cultivars studied, while only partial recovery was observed for Indica and tropical Japonica cultivars. Long-term chilling led to only a slight reduction in the capacity for LHCII phosphorylation in a temperate Japonica rice, while it was inhibited by 45% in a tropical Japonica type. The results indicate that the responses of CO(2) assimilation rate and photochemical efficiency significantly vary among ecologically divergent cultivars of rice to chilling, as does their rate of recovery from chilling. Additionally, maintenance and/or development of resistance to the loss in capacity for the phosphorylation of LHCII, and other thylakoid proteins associated with PSII, may help to prevent photodamage.