Alteration of the cell surface during the vegetative cell cycle of the unicellular green alga Chlamydomonas reinhardtii
Voigt, J. | Hinkelmann, B. | Liebich, I. | Mix, M.
Alterations of the cell surface during the vegetative cell cycle of the unicellular green alga Chlamydomonas reinhardtii were investigated using polyclonal antibodies against the purified and subsequently deglycosylated insoluble cell wall component and against a 100 kDa polypeptide of the deglycosylated, chaotrope-soluble wall fraction, respectively. Both antibodies recognized epitopes within the non-glycosylated domains of a '150 kDa' chaotrope-soluble glycoprotein (= GP3B) localized in the outer layers of the C. reinhardtii cell wall. Immunofluorescence studies indicated that both antibodies reacted with the surface of 'late' sporangia (harvested 1 h before liberation of the zoospores), but not with the cell surfaces of released zoospores, growing cells and young sporangia, respectively. After pretreatment with aqueous LiCl, however, the cell surfaces of zoospores, growing cells and young sporangia became accessible to these particular antibodies. Highly purified preparations of the insoluble wall fraction revealed strong immunofluorescence with both antibodies but not with the corresponding preimmune sera. Based on these data, we concluded that the antigenic sites of the insoluble glycoprotein framework of the C. reinhardtii wall are masked by LiCl-soluble glycoproteins in single cell stages and young sporangia, but not or to a lesser extent in the case of the mother walls of 'late' sporangia. The conclusion was supported by findings that (I) the multilayered structure of the mother-cell wall was disturbed in 'late', but not in young sporangia and that (II) the amounts of chaotrope-soluble cell wall glycoproteins present in the LiCl-extracts from intact sporangia decreased during ripening of the sporangia.
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