II.光合成の環境適応機構(光合成とゲノム進化から探る植物の環境適応機構)(2002年度神奈川大学共同研究奨励助成研究成果報告)

概要

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Diatom species of Coscinodiscus centralis Ehrenberg was widely distributed in North Water Polynya in April and May 1998. This species often showed maximum cell densities near to the sea surfaces. Its photosynthetic rates did not show any photoinhibition up to 475 μmol photons m^<-2>s^<-1> and an index of onset of light saturation represented as I_K was 115 μmol photons m^<-2>s^<-1>. Responses of this species to the strong light intensity at low temperature should be supported both by an initial slope of α and by a maximum rates of p_s^b in photosynthetic rate-light intensity curve (P-I curve). Its a and p_s^b at 0℃ were not similar to those estimated in the past studies in polar sea and were 3.35 × 10^<-2> (mgC mgChla^<-1> hour^<-1>)/(μmol photons m^<-2>s^<-1>) and 3.84 mgC mg Chla^<-1> hour^<-1>, respectively. Its higher p_s^b was maintained against suppression of electron transport rates and carboxylation rates by Ribulose bisphosphate carboxylase/oxygenase (RuBisCO) at low temperatures. Relative electron transport rates (ETR) and carboxylation rates by RuBisCO decreased by 60 and 47% with temperature decrease form 10 to 0℃, respectively, although photochemical reactions of quantum yield of photosystem II decreased only by 12%.
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