Graduate Thesis Or Dissertation
 

Cell wall formation in Fucus zygotes : cellulose synthesis and deposition after fertilization

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  • Under defined cultural conditions, large populations of zygotes of the brown algae Fucus vesiculosus L. and F. distichus L. Powell synchronously form a cell wall shortly after fertilization. Intact cell walls, free of cytoplasm and maintaining shape properties of early stages of embryo development, have been isolated from these zygotes. Removing components of the wall soluble in 0.25 N HC1, 3% Na₂CO₃ and 10% KOH at 110° C does not affect the shape properties of these isolated walls. Chromatography of acid and enzymatic hydrolysates of the remaining cell wall material identified the component which maintains cellular shape as the β -1, 4-glucan, cellulose. Neither β-1, 3- linkages nor protein are detectable in this cellulose fraction. Cellulose is not detectable in eggs but is present in zygotes within 20 minutes following fertilization. Incorporation of radioactivity from the precursors NaH¹⁴CO₃ and ³H-glucose confirmed that at least a portion of this cellulose is newly synthesized after fertilization with the highest rate of synthesis occurring in this first 20 minute period. During the first 24 hours of development the greatest amount of cellulose accumulates during the first four hours after fertilization, and most, if not all, of this cellulose is found associated with the cell wall and not the cytoplasm. This evidence suggests that the assembly, and possibly the synthesis of cellulose, occurs at the plasmalemma or extracellularly. Use of specific inhibitors indicated that cellulose synthesis requires cellular energy and neither cellulose synthesis nor cellulose deposition is regulated by genetic controls at transcription or translation. The evidence is consistent with the hypothesis that cellulose-synthesizing enzymes are pre-formed in the egg and activated upon fertilization. A particulate β-1,3-glucanase which is solubilized by Triton-X was isolated from zygotes and shown to release only glucose from the storage β-1,3-glucan (laminarin) purified from eggs and zygotes. Breakdown of laminar in by this exo-β- 1, 3-glucanase may provide substrates used for cellulose synthesis at the time of cell wall formation. Cellulose synthesis and deposition into a completely new cell wall formed synchronously in a single-cell population of Fucus zygotes can now serve as a model system to study mechanisms and regulation of cell wall biogenesis.
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