Temperature acclimation of the photosynthetic apparatus in an evergreen shrub, Nerium oleander

Abstract

It is known that temperature dependence of the photosynthetic rate changes with growth temperatures. As one of the causes of this change, changes in thermal tolerance of photosynthetic enzymes have been suggested (Badger et al. 1982, PC&E). However, the photosynthesis-temperature curves still differ at temperatures where the enzymes seem to be stable. We have suggested that changes in the limiting step of photosynthesis with growth temperatures can alter temperature dependence of photosynthesis (Hikosaka 1997, Ann Bot; Hikosaka et al. 1999, PC&E). In the present study, Nerium oleander plants were grown at 20 and 35oC and their gas exchange characteristics and photosynthetic apparatus were analysed. Temperature dependence of the light-saturated rate of photosynthesis at ambient CO2 (P360) differed between plants grown at different temperatures: P360 at 35oC was higher than that at 20oC in 35oC-grown plants, while P360 was similar between 20 and 35oC in 20oC-grown plants. However, initial slope of the CO2 dependence of the photosynthetic rate exhibited similar temperature dependence irrespective of growth temperatures. The ratio of the initial slope to RuBPCase (ribulose-1,5-bisphosphate carboxylase) content was also similar between plants grown at different temperatures. Analyses with gas exchange and chlorophyll fluorescence suggested that the CO2 compensation point and CO2 concentration at chloroplasts were similar between plants grown at different temperatures. These results suggest that P360 was limited by RuBPCase activity except for that at 35oC in 20oC-grown plants. We concluded that changes in the limiting step resulted in the different temperature responses of the photosynthesis between plants grown at different temperatures.