Seasonal Variation of Phosphoenolpyruvate Carboxylase Specific Activity in Fifteen Species Exhibiting Facultative or Obligate Crassulacean Acid Metabolism

Abstract

For 16 months the specific activity of the CAM key-enzyme PEP carboxylase (PEP-C) was determined monthly in twelve Sedum species previously shown to exhibit facultative or obligate CAM, as well as in Aeonium castello-paivae, Sempervivum nevadense and Kalanchoe daigremontiana. In all species examined the PEP-C activity showed a seasonal fluctuation with maxima during the summer from 8- to 30-fold higher than winter values. For most species the seasonal fluctuation correlated significantly with temperature and, to a lesser extent, with irradiation; no correlation was present with precipitation in garden-grown plants. Plants grown in greenhouse and garden showed corresponding seasonal fluctuations. Specific PEP-C activity, however, was restored to the summer level upon transfer to a growth chamber (21/15 °C, LD) in October. To determine the controlling climatic factor for this growth room-induced increase in PEP-C activity, the influence of light intensity, photoperiod and temperature on PEP-C activity was investigated in Sedum rupestre. Daytime temperature appeared to be the most influential factor, whereas light intensity had a small but significant effect.