© 2007 Heron Publishing—Victoria, Canada
Photosynthetic activity in winter needles of the evergreen tree Taxus cuspidata at low temperatures
Ayumi Tanaka
Institute of Low Temperature Science, Hokkaido University, W8 N10, Sapporo 060-0819, Japan (e-mail: ayumi@pop.lowtem.hokudai.ac.jp) / Received May 8, 2006; accepted July 12, 2006; published online February 1, 2007
Summary
Photosystems harvest light energy, yet this energy cannot be efficiently employed for CO2 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 °C, their chloroplasts
gradually dispersed to the edges of the cells, as in the summer. Acclimation-dependant relocalization coincided with changes
in CO2 uptake. Examination of photosystem II fluorescence kinetics in winter needles indicated that the quinone electron acceptor
(QA) reduction rate exceeded the QA oxidation rate at low temperatures. The majority of QA remained reduced even when winter needles were subjected to a temperature of –5 °C at low irradiance.
Keywords:
electron transport, fluorescence, frost, gas exchange, photosynthesis.
