title: Rubisco activase is a key regulator of non-steady-state photosynthesis at any leaf temperature and, to a lesser extent, of steady-state photosynthesis at high temperature.
abstract: The role of Rubisco activase in steady-state and non-steady-state photosynthesis was analyzed in wild-type (Oryza sativa) and transgenic rice that expressed different amounts of Rubisco activase. Below 25°C, the Rubisco activation state and steady-state photosynthesis were only affected when Rubisco activase was reduced by more than 70%. However, at 40°C, smaller reductions in Rubisco activase content were linked to a reduced Rubisco activation state and steady-state photosynthesis. As a result, overexpression of maize Rubisco activase in rice did not lead to an increase of the Rubisco activation state, nor to an increase in photosynthetic rate below 25°C, but had a small stimulatory effect at 40°C. On the other hand, the rate at which photosynthesis approached the steady state following an increase in light intensity was rapid in Rubisco activase-overexpressing plants, intermediate in the wild-type, and slowest in antisense plants at any leaf temperature. In Rubisco activase-overexpressing plants, Rubisco activation state at low light was maintained at higher levels than in the wild-type. Thus, rapid regulation by Rubisco activase following an increase in light intensity and/or maintenance of a high Rubisco activation state at low light would result in a rapid increase in Rubisco activation state and photosynthetic rate following an increase in light intensity. It is concluded that Rubisco activase plays an important role in the regulation of non-steady-state photosynthesis at any leaf temperature and, to a lesser extent, of steady-state photosynthesis at high temperature.
authors.affiliation: Department of Applied Plant Science, Graduate School of Agricultural Science, Tohoku University, 1-1 Tsutsumidori-Amamiyamachi, Aoba-ku, Sendai 981-8555, Japan. wataru.yamori@biochem.tohoku.ac.jp
authors.forename: Wataru
authors.initials: W
authors.lastname: Yamori
authors.forename: Chisato
authors.initials: C
authors.lastname: Masumoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Fukayama
authors.forename: Amane
authors.initials: A
authors.lastname: Makino
mesh_terms: D002245:Carbon Dioxide / Q000378:metabolism*; D002734:Chlorophyll / Q000378:metabolism; D004789:Enzyme Activation; D018506:Gene Expression Regulation, Plant; D006358:Hot Temperature; D008027:Light; D012275:Oryza / Q000201:enzymology* / Q000235:genetics / Q000502:physiology / Q000528:radiation effects; D010788:Photosynthesis / Q000502:physiology*; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism / Q000502:physiology / Q000528:radiation effects; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified; D012273:Ribulose-Bisphosphate Carboxylase / Q000235:genetics / Q000378:metabolism*; D013696:Temperature
chemical_list: D010940:Plant Proteins; C054765:rca protein, plant; D002734:Chlorophyll; D002245:Carbon Dioxide; D012273:Ribulose-Bisphosphate Carboxylase