Sulfation of fucoidin in focus embryos: III. Required for localization in the rhizoid wall

Abstract

Zygotes of the brown alga Fucus distichus L. Powell accumulate a sulfated polysaccharide (fucoidin) in the cell wall at the site of rhizoid formation. Previous work indicated that zygotes grown in seawater minus sulfate do not sulfate the preformed fucan (an unsulfated fucoidin) but form rhizoids. Under these conditions, we determined whether sulfation of the fucan is required for its localization in the rhizoid wall. This was accomplished by developing a specific stain for both the fucan and fucoidin. Using a precipitin assay, we demonstrated in vitro that the lectin ricin (RCAz) specifically complexes with both the sulfated and desulfated polysaccharide. No precipitate is observed when either is incubated in 0.1 M o-galactose or when RCAI is mixed with laminarin or alginic acid, the other major polysaccharides in Fucus. RCA~ conjugated with fluorescein isothiocyanate (FITC) is also shown to bind specifically to fucoidin using a filter paper (DE81) assay. When added to zygotes, RCArFITC binds only to the site of fucoidin localization, i.e., the rhizoid cell wall. However, RCArFITC is not observed in the rhizoid wall of zygotes grown in the absence of sulfate. This observation is not due to the inability of RCAI-FITC to bind to the fucan in vivo. Chemically desulfated cell walls that contained fucoidin in the rhizoid wall bind RCAI-FITC only in the rhizoid region. Also, the concentration of fucose-containing polymers and polysaccharides that form precipitates with RCA~ is the same in embryos grown in the presence or absence of sulfate. If sulfate is added back to cultures of zygotes grown without sulfate, fucoidin is detected at the rhizoid tip by RCA[-FITC several hours later. These results support the conclusion that the enzymatic sulfation of the fucan is a modification of the polysaccharide required for its localization and/or assembly into a specific region of the cell wall. KEY WORDS Fucus distichusricin 9 fluorescence microscopy fucoidin sulfation cell wall cytoplasmic localization rhizoidThe localization of subcellular components into specific regions of a variety of plant and animal cells is a common and important aspect of cellular differentiation (c.f. reference 17). However, the mechanism by which macromolecules are sequestered into localized regions or structures of cells is not well understood. The rhizoid of the Fucus zygote provides a model system to investigate the regulation of intracellular localization. Previous reports indicated that a new and different sulfated polysaccharide is deposited in only that region of the zygote cell wall that forms the rhizoid (4, 20).

EFFECTS OF BROMIDE AND IODIDE ON STALK SECRETION IN THE BIOFOULING DIATOM ACHNANTHES LONGIPES (BACILLARIOPHYCEAE)1

“…This implies that sulfate plays an integral role in polymer assembly and/or secretion and gel formation, not only in stalk secretion but also in insoluble EPS production. Sulfation of fucan is required for adhesion (Crayton et al 1974) and localized insertion of polysaccharides into the rhizoid wall of Fucus zygotes (Hogsett andQuatrano 1978, Quatrano 1982). Binding between neighboring sulfated oligosaccharide side chains on glycoproteins is attributed to cell wall assembly or attachment to the cell membrane in Chlamydomonas reinhardii and Lobomonas piriformis (Roberts et al 1980).…”

Sulfation of a cell surface glycoprotein correlates with the developmental program during embryogenesis of Volvox carteri.

“…Sulfated polysaccharides were also implicated in embryogenesis of sea urchins; it is assumed that synthesis of sulfated polysaccharides is an indispensable step for postgastrular development (24)(25)(26). Studies on the embryogenesis of the brown alga Fucus led to the conclusion that the sulfation of polysaccharides (fucan) is a modification required for its localization into a specific region of the cell wall (27,28).…”

Fucoidans of brown algae: Biosynthesis, localization, and physiological role in thallus

“…When embryos were grown in a sulfateless medium, in which the synthesis of sulfated polysac charides is impossible, zygotes and embryos lost the ability to attach to the substrate and floated freely in the water. When sulfates were added to the water, sul fated fucoidans were detected histochemically in the rhizoids of 2 cell embryos 6 h later; young plantlets successfully attached to the substrate [41,52].…”