CARBOHYDRATES IN IRIDEAE LAMINARIOIDES (RHODOPHYCEAE)

Abstract

Iridaea laminarioides plants were collected at 4 times of the year, extracted with alcohol and analysed for soluble sugars. No free reducing or total sugars were found, but crystalline dulcitol was isolated from the alcoholic extract of the plant. A water soluble carbo-hydrate consisting of galactose units and containing a S group was isolated from the alcohol-extracted material. This carbohydrate proved to be a Na sulfuric acid ester of galactan. Contrary to the theory held by investigators that starch is never found in red algae, it was found to be present in Iridaea laminarioides. The plant does not contain any cellulose, and since the content of galactan is about 30% of its dry weight and constitutes the main bulk of the plant, it appears that this substance plays the same part in building up its cell wall as does cellulose in that of the higher plants. Since there are no free sugars in this plant, other than dulcitol, it is conceivable that the polysaccharide galactan is built up from this substance by a mechanism anal-ogous to that of cellulose from glucose in the higher plants.