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Daily photosynthetic and C-export patterns in winter wheat leaves during cold stress and acclimation
Evangelos D. Leonardos1, Leonid V. Savitch, Norman P. A. Huner
1Department of Plant Agriculture, Division of Horticultural Science, University of Guelph, Guelph, ON, N1G 2W1, Canada Agriculture and Agri-Food Canada, Eastern Cereal and Oilseed Centre, Ottawa, ON, K1A 0C6, Canada Department of Plant Sciences, University of Western Ontario, London, ON, N6A 5B7, Canada Department of Plant Physiology, Umeå Plant Science Centre, Umeå University, Umeå, S-901 87, Sweden.
Abstract:
Diurnal patterns of whole-plant and leaf gas exchange and 14C-export of winter wheat acclimated at 20 and 5 degrees C were determined. The 5 degrees C-acclimated plants had lower relative growth rates, smaller biomass and leaf area, but larger specific leaf weight than 20 degrees C plants. Photosynthetic rates in 20 degrees C and 5 degrees C-acclimated leaves were similar; however, daytime export from 5 degrees C-acclimated leaves was 45% lower. Photosynthesis and export remained steady in 20 degrees C and 5 degrees C-acclimated leaves during the daytime. By comparison, photosynthesis in 5 degrees C-stressed leaves (20 degrees C-acclimated plants exposed to 5 degrees C 12 h before and during measurements) declined from 70 to 50% of the 20 degrees C-acclimated leaves during the daytime, while export remained constant at 35% of the 20 degrees C-acclimated and 60% of the 5 degrees C-acclimated leaves. At high light and CO2, photosynthesis and export increased in both 20 degrees C and 5 degrees C-acclimated leaves, but rates in 5 degrees C-stressed leaves remained unchanged. At all conditions daytime export was greater than nighttime export. Taken together, during cold acclimation photosynthesis was upregulated, whereas export was only partially increased. We suggest that this reflects a requirement of cold-acclimated plants to both sustain an increased leaf metabolic demand while concomitantly supporting translocation of photoassimilates to overwintering sinks.