Interactions between light and temperature during the in vitro as well as in situ modulation of phosphoenolpyruvate carboxylase in leaves of a C3 plant Pisum sativum L.

The C4 phosphoenolpyruvate carboxylase (PEPC) is well known for its modulation by light and temperature. We have attempted to address such coordinated effects of light and temperature on C3 PEPC in leaves of Pisum sativum. Experiments were done with dark-adapted leaf discs as well as with leaves collected at different times during the day and in each month during the year. The modulation of C3 PEPC by temperature was much stronger than that by light. The optimum temperature for in vitro activity of C3 PEPC was 25°C while 20°C was sub-optimal and 30°C to 45°C were supra-optimal. The photo-activation of PEPC was more at 25°C than at 45°C. The activation of C3 PEPC by temperature was more in the dark than in the light. In in situ conditions, a diurnal rhythm in the activity and regulatory properties of C3 PEPC was more prominent at colder than at warm temperatures. However, no consistent trends in the seasonal changes in PEPC activity/ regulatory properties were observed. Scatter plots suggested that light had a greater influence on PEPC activity while temperature exerted a much greater effect on its regulatory properties. Thus, C3 PEPC was also modulated by a natural variation in light and temperature under in situ conditions. These observations correlated well with the light and temperature requirements of C3 plants.