Effect of Temperature on the Activity of Carboxylases in Tropical and Temperate Gramineae

Abstract

Temperate Gramineae show maximal net photosynthesis at 20–5 °C, whereas tropical Gramineae have maxima between 30 and 35 °C. Moreover, it has been suggested that different carboxylation reactions are involved in the two groups. The present study of the temperature dependance of in vitro ribulose-1,5- diphosphate (RuDP), and phosphopyruvate (PEP) carboxylases indicates that the two enzymes have clearly marked differences in temperature sensitivity. RuDP carboxylase, present in the temperate and tropical species studied, showed maximal activity around 20–5 °C except in Zea. By contrast, PEP carboxylase activity in all species was maximal between 30 and 35 °C. The data imply that activity and temperature sensitivity of the relevant carboxylase enzymes may well be a significant limiting factor in leaf photosynthesis, even at light saturation.