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Title: RESPONSES OF PHOTOSYNTHESIS AND PHOSPHORYLATION OF THE LIGHT-HARVESTING COMPLEX OF PHOTOSYSTEM II TO CHILLING IN ECOLOGICALLY DIVERGENT CULTIVARS OF RICE.

Author
item Gesch, Russell - Russ
item HEILMAN, JAMES - TEXAS A&M UNIVERSITY

Submitted to: Environmental and Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/19/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Rice, one of the most important food crops in the world, is sensitive to cold but non-freezing temperatures at all stages of development. However, the degree of sensitivity among different varieties may be quite substantial in light of the fact that rice is grown in many different parts of the world. This study was conducted to address the effects of cold temperatures on photosynthesis in several varieties of rice. The varieties chosen for the study came from geographical areas differing in their climates. Both the light transduction and atmospheric carbon dioxide fixation pathways of photosynthesis were found to be sensitive to cold, but the responses differed significantly among the varieties tested. Further testing showed that the dissipation of light energy under cold-stress during the day, which appeared to be greatest in varieties which were least sensitive to cold temperature, may be an important way for rice to alleviate certain problems associated with cold. By better understanding the physiological mechanisms controlling tolerance to cold temperatures in rice, breeders and geneticists will be able to carefully select for improved cold- tolerant varieties of rice. Increased cold-tolerance in rice will help producers in areas where periodic cold weather during rice production can be a problem.

Technical Abstract: Rice (Oryza sativa L.), which is susceptible to chilling damage, is cultivated in diverse environments ranging from tropical to temperate regions. The present study was conducted to evaluate the photosynthetic responses of five different cultivars of rice to chilling over several days, and to test the hypothesis that their capacity for phosphorylation of the light-harvesting protein complex of PSII (LHCII) is differentially effected. Seedlings were grown to the three-leaf stage at 28/22oC day/night temperature and then transferred to 10/8oC day/night for 6 d, followed by 3 d of recovery at higher temperatures. Among the cultivars studied, photosynthesis decreased by 40 to 89% within 3 d after transfer to 10/8oC. Photochemical efficiency of PSII, measured by FV/FM, followed a similar trend. During recovery, photosynthesis and photochemistry fully recovered in two temperate Japonica cultivars studied, while only partial recovery was observed for Indica and tropical Japonica cultivars. 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. Inhibition and recovery from chilling, of both the light and dark processes of photosynthesis, differed significantly among the cultivars studied. Results indicate that 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.