Temperature responses of ribulose bisphosphate carboxylase and photosynthetic capacity in arctic and tropical phytoplankton

Abstract

When assayed near respective in situ temperatures, ribulose bisphosphate carboxylase (RuBPC) exhibits a greater response to increasing temperature in arctic than in tropical phytoplankton. This was also true when the Arrhenius activation energy (E sub(a)) was compared for a range of intermediate temperatures. This difference in temperature response and E sub(a) for RuBPC is consistent with the temperature response of photosynthetic capacity, but is contrary to the general observation that cold-environment ecotherms (organisms whose internal temperature conforms to that of the environment) have physiological processes with lower E sub(a)'s. Analysis suggests that the genotypic adaptation of qualitative enzyme temperature responses in marine phytoplankton is related to the vertical structure of the environment and to a suite of variables of which temperature is only one. Quantitatively, however, arctic phytoplankton do not appear to adapt to cold by increasing RuBPC levels per unit pigment biomass.