The Dark Fixation of CO2 by Succulent Leaves: The First Products.

Abstract

An apparatus which permits intact leaves to be exposed to C14O2 in complete darkness for short periods of time has been devised. Using this apparatus, the major products of the dark fixation of C14O2 by Bryophyllum calycinum have been identified as malate and aspartate during a 6 second fixation period. The kinetics of labeling from these compounds during longer dark periods indicate that they must arise from a common precursor. This precursor has been identified as oxaloacetate. The enzyme mediating the initial fixation, phosphoenolpyruvylcarboxylase, has been identified in homogenates of B. calycinum. A scheme to account for the initial fixation of CO2 by succulents is presented.