Studies on 14CO2-assimilation in marine rhodophyceae

Experiments on enzymatic (in vitro) and in vivo CO₂-fixation using a variety of marine Rhodophyceae such as Porphyra umbilicalis (L.) J.Ag., Rhodomela confervoides (Huds.) Silva, Corallina officinalis L. and Chondrus crispus Stackh. revealed that carbon assimilation in the Rhodophyceae is almost exclusively performed by photosynthesis via ribulose-1, 5-di-phosphate carboxylase, whereas light-independent CO₂-fixation via -carboxylation by phosphoenolpyruvate carboxykinase scarcely exceeds 1% of the total carbon fixation potential of the plants. Activity of phosphoenolpyruvate carboxylase could not be detected. With respect to the main accumulation products of photosynthetic CO₂-fixation, the Rhodophyceae investigated are not uniform: Corallina officinalis L., Rhodymenia palmata (L.) Grev., and Gigartina stellata (Stackh.) Batt. have been found to accumulate ¹⁴C in the neutral compound floridoside (=2-O-glycerol--D-galactopyranose), whereas Delesseria sanguinea (Huds.) Lamour., Ceramium cubrum (Huds,) C.Ag., and Rhodomela confervoides (Huds.) Silva, representing members of the Delesseriaceae, Ceramiaceae and Rhodomelaceae, respectively, do not photosynthesize floridoside, but show intense ¹⁴C-labelling in an acidic constituent, mannosidoglycerate (= digeneaside). This compound is reported for the first time as a rapidly ¹⁴C-labelled and accumulated photosynthate in a variety of red algal species exclusively belonging to the Ceramiales.