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Acclimation of spinach plants grown at 25 degrees C to a temperature of 10 degrees C for 10 d resulted in an increased capacity for leaf photosynthesis in saturating light and CO2, but not at ambient CO2 concentrations, Gas exchange and chlorophyll fluorescence measurements indicated that acclimation was accompanied by an increased capacity for the regeneration of ribulose-1,5-bisphosphate. Changes in starch, solubIe carbohydrates and activities of sucrose-P synthase and ADP-glucose pyrophosphorylase were measured during the acclimation process, There was an initial increase in starch and sucrose during the first 2 d, but these then declined, There was an increase in the capacity for sucrose synthesis during low temperature acclimation, evidenced by an increase in the maximum activity of sucrose-P synthase activity and an increase in partitioning of (CO2)-C-14 into sucrose, but there was no increase in the activity of ADP-glucose pyrophosphorylase or carbon partitioning into starch.