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Plant Physiology 58:224-231 (1976) © 1976 American Society of Plant Biologists Cell Wall Assembly in Fucus ZygotesI. Characterization of the Polysaccharide Components 1,2a Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon 97331, b Marine Biological Laboratories, Woods Hole, Massachusetts 02543
Fertilization triggers the assembly of a cell wall around the egg cell of three brown algae, Fucus vesiculosus, F. distichus, and F. inflatus. New polysaccharide polymers are continually being added to the cell wall during the first 24 hours of synchronous embryo development. This wall assembly involves the extracellular deposition of fibrillar material by cytoplasmic vesicles fusing with the plasma membrane. One hour after fertilization a fragmented wall can be isolated free of cytoplasm and contains equal amounts of cellulose and alginic acid with no fucose-containing polymers (fucans) present. Birefringence of the wall caused by oriented cellulose microfibrils is not detected in all zygotes until 4 hours, at which time intact cell walls can be isolated that retain the shape of the zygote. These walls have a relatively low ratio of fucose to xylose and little sulfate when compared to walls from older embryos. When extracts of walls from 4-hour zygotes are subjected to cellulose acetate electrophoresis at pH 7, a single fucan (F1) can be detected. By 12 hours, purified cell walls are composed of fucans containing a relatively high ratio of fucose to xylose and high levels of sulfate, and contain a second fucan (F2) which is electrophoretically distinct from F1. F2 appears to be deposited in only a localized region of the wall, that which elongates to form the rhizoid cell. Throughout wall assembly, the polyuronide block co-polymer alginic acid did not significantly vary its mannuronic (M) to guluronic (G) acid ratio (0.33-0.55) or its block distribution (MG, 54%; GG, 30%; MM, 16%). From 6 to 24 hours of embryo development, the proportion of the major polysaccharide components found in purified walls is stable. Alginic acid is the major polymer and comprises about 60% of the total wall, while cellulose and the fucans each make-up about 20% of the remainder. During the extracellular assembly of this wall, the intracellular levels of the storage glucan laminaran decreases. A membrane-bound
3 A portion of this research constitutes parts of a dissertation presented to The Graduate School of Oregon State University in partial fulfillment for the degree of Doctor of Philosophy. 1 This research was supported by Grant GB 37149 from the National Science Foundation and Grant GM 19247 from the Public Health Service and a fellowship from the Royal Norwegian Society of Science and Technology to R. S. Q. during a stay at the Institute of Marine Biochemistry, Trondheim, Norway. 2 This paper and subsequent ones in this series are dedicated to the outstanding pioneering work in the field of algal polysaccharide chemistry by Professor Arne Haug (deceased May 1975) of the Institute of Marine Biochemistry in Trondheim, Norway. This article has been cited by other articles:
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-1, 3-exoglucanase is found in young zygotes which degrades laminaran to glucose. It is postulated that hydrolysis of laminaran by this glucanase accounts, at least in part, for glucose availability for wall biosynthesis and the increase in respiration triggered by fertilization. The properties and function of alginic acid, the fucans, and cellulose are discussed in relation to changes in wall structure and function during development. 
