C4-metabolism in marine brown macrophytic algae

Abstract

Marine brown macroalgae including Macrocystis integrifolia, Nereocystis luetkeana, Lessoniopsis littoralis, Laminaria saccharina, Fucus serratus and some further representatives of the Laminariales and Fucales (Phaeophyta) have been investigated with respect to their remarkably high potential for β-carboxylation of phosphoenolpyruvate supplementing photosynthetic CO2 fixation. Kinetic tracer studies indicate that 14C-labelling of C4 acids such as aspartate and malate is not restricted to dark periods, but also occurs during photosynthesis. Rates of carbon fixation into C4 compounds are approximately equal in the light and in the dark. Distribution of 14C between C1 and C4 atoms of aspartate suggests carbon flow from early occurring photosynthates such as 3-phosphoglycerate to C4 compounds including aspartate and malate. In brown macroalgae dark carbon fixation via β-carboxylation of phosphoenolpyruvate is therefore assumed to be quantitatively and qualitatively integrated into photosynthetic C02 assimilation thus yielding a preciable 14C-labelling of C4 dicarboxylic acids.The underlying reactions and conversions are basically different from C4 photosynthesis and should preferably be termed as C4 metabolism. © 1981, Walter de Gruyter. All rights reserved.