The composition and development of cell walls of Fucus embryos.

Changes in the structure and composition of cell walls of Fucus gardneri Silva were related to embryo development. Results of histochemical treatments of walls from embryos of different ages were compared with those of differential extractions and electronmicroscopic examinations of isolated walls. At 24 h after fertilization alginic acid, fucoidin and cellulose were structural constituents of the embryo wall. The distribution of alginic acid and cellulose was uniform over the cell walls of embryos of any age, but fucoidin was concentrated at the rhizoid end of cell walls isolated from germinated embryos. Evidence is presented for the presence of sulfated xylogalactofucoglucuronan and β,1-3 glucan in the embryo cell-wall. Electron micrographs of untreated and differentially extracted cell walls showed that alginic acid comprised the fibrillar material and fucoidin comprised the amorphous material of the wall. Fucus eggs do not have cell walls and the zygotes began wall synthesis within 40 min after fertilization. During the first 2 h there was a rapid deposition of alginic acid. After 4 h the wall thickness increased linearly through 24 h. Embryos treated with cycloheximide ceased wall growth after 6 h. Wall isolated from 24-h-old cycloheximide-treated embryos resembled wall isolated from control embryos 2-4 h old.