Plants of `Rotundifolia' holly (Ilex crenata Thunb.) were grown for 3 weeks with root zones at 30,34,38, or 42C for 6 hours daily to evaluate the effects of supraoptimal root-zone temperatures on various photosynthetic processes. After 3 weeks, photosynthesis of plants grown with root zones at 38 or 42C was below that of plants grown at 30 or 34C. Chlorophyll and carotenoid levels decreased while leaf soluble protein levels increased as root-zone temperature increased. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity per unit protein and per unit chlorophyll responded quadratically, while RuBisCO activity per unit fresh weight increased linearly in response to increasing root-zone temperature. Results of this study suggest that `Rotundifolia' holly was capable of altering metabolism or redistributing available assimilates to maintain CO2 assimilation rates in response to increasing root-zone temperatures.
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