The chemical composition and structure of the cell wall of Hydrodictyon africanum Yaman

Abstract

Cell-wall preparations of the coenocytes-of H. africanum have been obtained. The walls are approximately 5.5 u thick and represent 39.2% of the dry weight of the whole cell. An analysis of the wall has been made with respect to the following fractions a-cellulose fraction (69%), hemicellulose fraction (16%), protein (4%), lipid (7%) and ash (0.3%), which accounts for over 96% of the material. The cell wall appears as a transparent colorless membrane and 2 pairs of thin circular pads, approximately 110 [mu] in diameter, can be seen at opposite poles corresponding to the position of neighboring cells in the intact colony. The walls stain with the normal histochemical tests for cellulose. The wall is made up of 3 layers, thin inner and outer layers and a thick middle layer. The middle layer is a 2-phase system in which microfibrils approximately 30-40 A in diameter are closely packed and enclosed in a continuous matrix. This layer is further divided by very thin lamellae which run parallel to the cell surface, and the microfibrils in any one section of it lie mainly in 1 direction around the wall. The hemicellulose fraction contains glucose, mannose and traces of xylose and arabinose. It is probably present as a glucomannan. The [alpha]-cellulose fraction is composed of polymers containing glucose and mannose. The occurrence of the mannose in the [alpha]-cellulose fraction with respect to the composition of the microfibril is discussed. Pores seen as oval in shape (1 [mu] x 0.4 [mu] in diameter) which are bounded by a dark-staining membrane traverse the wall.