title: Photosynthetic activity in winter needles of the evergreen tree Taxus cuspidata at low temperatures.
abstract: Photosystems harvest light energy, yet this energy cannot be efficiently employed for CO(2) assimilation at the below-freezing temperatures to which plants are typically exposed during winter in the temperate and boreal zones. To elucidate the mechanisms whereby this energy is dissipated, I evaluated performance of photosystems in winter needles of the evergreen tree Taxus cuspidata Sieb. et Zucc. Chloroplasts were localized adjacent to plasma membranes in needle cells in summer, whereas they congregated together in the centers of the cells during winter. When winter needles were acclimated to a temperature of 20 degrees C, their chloroplasts gradually dispersed to the edges of the cells, as in the summer. Acclimation-dependent relocalization coincided with changes in CO(2) uptake. Examination of photosystem II fluorescence kinetics in winter needles indicated that the quinone electron acceptor (Q(A)) reduction rate exceeded the Q(A) oxidation rate at low temperatures. The majority of Q(A) remained reduced even when winter needles were subjected to a temperature of -5 degrees C at low irradiance.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, W8 N10, Sapporo 060-0819, Japan. ayumi@pop.lowtem.hokudai.ac.jp
authors.forename: Ayumi
authors.initials: A
authors.lastname: Tanaka
mesh_terms: D000064:Acclimatization / Q000502:physiology; D002245:Carbon Dioxide / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism / Q000528:radiation effects* / Q000648:ultrastructure; D003080:Cold Temperature; D004579:Electron Transport / Q000528:radiation effects; D005453:Fluorescence; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction / Q000528:radiation effects; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000378:metabolism / Q000528:radiation effects; D018515:Plant Leaves / Q000378:metabolism / Q000528:radiation effects* / Q000648:ultrastructure; D011808:Quinone Reductases / Q000378:metabolism; D012621:Seasons; D020946:Taxus / Q000378:metabolism / Q000528:radiation effects* / Q000648:ultrastructure
chemical_list: D045332:Photosystem II Protein Complex; D002245:Carbon Dioxide; D011808:Quinone Reductases