An analysis of photosynthetic response and adaptation to temperature in higher plants: temperature acclimation in the desert evergreen Nerium oleander L*

Abstract. Factors underlying the process of photosynthetic acclimation to temperature were investigated for the shrub Nerium oleander L. Ramets of a single clone were grown under day/night temperature regimes of 20°C/15°C or 45°C/32°C. Plants grown at the lower temperature regime possessed rates of photosynthesis twice that of the high-temperature grown plants when CO₂ fixation was measured at 20°C. In contrast, the plants grown at the high-temperature regime had twice the rate of CO₂ fixation of the 20°C/l 5°C-grown plants at a measurement temperature of 45° C. It was determined that the ability to acclimate to changes in temperature regime was present in fully mature leaves. A reciprocal transfer of plants between the two growth regimes resulted in the appearance of the CO₂ fixation characteristics appropriate to the new growth temperature after 12–14d. The response of CO₂ fixation to light, temperature, and CO₂ partial pressure and the temperature responses of soluble and membrane-bound photosynthetic enzyme systems were analysed to determine which components might be responsible for the superior photosynthetic performance of the 20°C/I5°C-grown plants at 20°C, and the enhanced high-temperature stability of the 45°C/32°C plants. The measured photosynthetic capacity of the 20°C/15°C plants could not be attributed to gross morphological, stomatal, or other physical changes, or to a general increase in the concentration of components of the photosynthetic process. Only a single enzyme, Fru-P₂ phosphatase, was affected to an extent similar to that of photosynthesis. The enhanced thermal stability of the 45°C/32°C plants may be attributed primarily to an enhanced stability of the chloroplast membrane-bound enzymatic activities and the stability of the photosynthetic carbon metabolism enzymes which require lighl for activation.