We have established an experimental system for mimicking the phenomenon of cool-temperature-induced chlorosis (CTIC) in rice plants (Oryza sativa L.). Rice seedlings were initially grown in darkness under cool-temperature conditions and then exposed to light and warm conditions to follow the expression of CTIC. Induction of CTIC in the sensitive cultivar (cv Surjamukhi) was bimodally dependent on the temperatures experienced during the initial growth in darkness. CTIC was maximally induced between 15 and 17°C. A positive correlation was demonstrated between induction of CTIC and the growth activity of shoots during growth in darkness. Electrophoretic and immunoblot analysis revealed that accumulation of NADPH-protochlorophyllide oxidoreductase in plastids was also bimodally dependent on the temperatures during the growth in darkness with minimum accumulation between 15 and 17°C, suggesting that the reduction of NADPH-protochlorophyllide oxidoreductase accumulation in plastids might be closely linked to a disturbance in transformations of plastids to etioplasts during the dark growth under the critical temperatures and thereby to the CTIC phenomenon. This was corroborated by electron microscopic observations. These results suggest that growth is one of the determining factors for the expression of CTIC phenotype in rice under cool temperature.
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