Authors: Renee A Lopez Karen S Renzaglia
Publish Date: 2016/01/06
Volume: 243, Issue: 4, Pages: 947-957
Abstract
Both male and female gametes of archegoniates are highly specialized cells surrounded by an extraprotoplasmic matrix rich in AGPs which are speculated to facilitate development and gamete fusion through Ca 2+ oscillations An additional layer the egg envelope forms around the egg periphery except at the fertilization pore and contains arabinoserich polymers that presumably impart flexibility for the rapidly growing zygote and embryo The abundant AGPs and arabinan pectins associated with the eggs of C richardii not only are integral to development fertilization and early embryogenesis but also may be involved in desiccation tolerance important to the survival of the reproductive gametophyteA defining feature of gametogenesis in archegoniates is the deposition of a special matrix outside of the plasmalemma of both egg and sperm cells that displaces the primary cell wall away from the protoplasm It is within this matrix that gamete differentiation occurs In leptosporangiate ferns maturation of the egg cell involves the deposition of a second specialized wall the socalled egg envelope that surrounds the cell except at the fertilization pore a narrow site where gamete fusion takes place We provide the first conclusive evidence of the macromolecular constituents in the unique structures surrounding fern egg cells before and after fertilization To test the hypotheses that the egg extracellular matrix contains arabinogalactan proteins AGPs as does the sperm cell matrix and that cell wall polysaccharides especially pectins are components of the egg envelope we examined the expression patterns of AGPs and cell wall constituents during oogenesis in Ceratopteris richardii Utilizing histochemical stains for callose cellulose and AGPs coupled with immunogold localizations employing a suite of monoclonal antibodies to cell wall components JIM13 JIM8 LM2 LM5 LM6 LM19 LM20 and anticallose we demonstrate that AGPs but not pectins are abundant in the matrix around egg cells and degrading neck canal and ventral canal cells during archegonial development A striking finding is that both AGPs and 15αlarabinan pectin epitopes are principle components of the egg envelope before and after fertilization suggesting that they are important in both egg maturation and gamete fusionWe thank Les Hickok for the Ceratopteris spores used in this study We also thank Bryan Piatkowski Amelia Merced Nicholas Flowers and Jason Henry for technical support and comments on the manuscript This work was supported by the National Science Foundation Grants DEB0423625 DEB0521177 DEB0638722
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