Regulation of Alginate Gelation During Wall Development in Fucus Embryos

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Alginate synthesis and de novo assembly into a cell wall by the fertilized egg of the brown alga. Fucus provides a simple system for studying plant cell wall formation. Alginate is a linear polymer of the two acidic sugars, mannuronate and guluronate, arranged in nongelling and gelling subunits. Recent work identified the intracellular site of synthesis of the gelling subunits as the Golgi apparatus. Alginate molecular size and the subunit length distributions of intracellular and extracellular alginate will be examined by electrophoresis after cleavage by specific enzymes. The ability of zygote alginate to gel in a seawater environment will be studied by labelling zygote sections with fluorescent hybridization probes of known chain length. The activities of two enzymes, one regulating alginate gelation (epimerase converts nongelling subunits to gelling subunits) and one causing its cleavage (lyase cuts alginate chains for wall expansion) will be correlated with wall development by enzyme microassays. Antisera to the purified enzymes will be prepared for immunogold ultrastructural localization during wall development. In vitro translation products of messenger RNA prepared form zygotes during development will be immunoprecipitated. This project will provide information on enzyme and mRNA controls of the synthesis, assembly, structure and modification of a gelling wall carbohydrate. %%% This project will provide detailed information on the control of a gelling plant cell wall polymer at the carbohydrate, protein and mRNA levels of control. This gelling/nongelling allows the cell wall components to adapt to growth while maintaining the integrity of the organism.