Abstract
Two Phaseolus vulgaris L. cultivars were grown at 20/15, 25/20, and 30/25 °C day/night tem peratures in growth chambers with a 16 h thermoperiod corresponding to the photoperiod. When the first trifoliolate leaf was fully expanded rates of CO2 exchange (CER) were measured at 27 °C and saturating light using infrared gas analysis. Stomatal (rs) and mesophyll resist ances, CO2 compensation points, activities of the enzymes ribulose bisphosphate carboxylase (RuBPCase), glycolate oxidase (GAO), malate dehydrogenase (MDH), and fructose-1,6 diphosphate (FDP), chlorophyll content, Hill activities, and leaf anatomy at both the light and electron microscope level were also investigated in these leaves. Rates of CO2 exchange in the light, transpiration rate, and chlorophyll content increased with increasing growth temperature while leaf thickness, specific leaf weight, RuBPCase activity, compensation point, and stomatal resistance decreased. Mesophyll resistance also decreased when calculated assuming zero chloroplast CO2 concentration (rmjo), but not when calculated assuming a chloroplast CO2 concentration equal to the CO2 compensation con centration (rm,g). Average leaf size was maximal in 25/20 °C plants while dark respiration, MDH activity, stomatal density, and starch were minimal. The activities of GAO and FDP and Hill activity were not affected by temperature pretreatment.
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