Properties of cell surface carbohydrates in sexual reproduction of the Closterium peracerosum–strigosum–littorale complex (Zygnematophyceae, Charophyta)

Abstract

TheClosterium peracerosum-strigosum-littorale complex is a best characterized zygnematophycean green alga with respect to the process of sexual reproduction. Intercellular communication mediated by two sex pheromones has been well documented in this organism, but information concerning direct cell-cell recognition and fusion of cells involved in conjugation processes has not yet been clarified. In this study, we examined the properties of cell surface carbohydrates in vegetative and reproductive cells using a variety of fluorescein isothiocyanate labeled lectins as probes. Among 20 lectins tested, 10 bound to the Closterium cell surface, and eight of these were specific for the cells involved in sexual reproduction. In addition, some of the lectins inhibited the progress of zygote formation. In particular, Lycopersicon esculentum lectin (LEL) and ConcanavalinA (ConA) considerably inhibited zygote formation (23.6% and 0% of zygotes formed, respectively, compared with the control). LEL mainly accumulated on conjugation papillae and on the surface and lumens of empty cell walls remaining after zygote formation. ConA bound to both vegetative and sexually reproductive cells and strongly accumulated on the conjugation papillae of the latter, indicating ConA binding material(s) are nonspecifically present in Closterium cells but some of the material(s) would be essential for zygote formation. These results suggest that different carbohydrates specifically recognized by these lectins are involved in cell recognition and/or fusion during conjugation processes in the C. psl. complex.

Concanavalin A Disrupts the Release of Fibrous Material Necessary for Zygote Formation of a Unicellular Charophycean Alga, Closterium peracerosum-strigosum-littorale Complex

“…complex are mixed in nitrogen-depleted medium, the following processes of sexual reproduction are observed: (i) mucilage secretion, (ii) sexual cell division to form gametangial cells, (iii) pair formation between opposite mating type gametangial cells, (iv) formation of conjugation papillae, (v) release of protoplasts (gametes) from the cells, and (vi) fusion of the gametes to form a zygote ( Ichimura, 1971 ; Sekimoto et al, 2012 ). We previously reported that Con A completely inhibits the zygote formation ( Hori et al, 2012 ). Even though the results indicated that the target molecule(s) of Con A plays important roles in zygote formation, the details of the stage influenced by Con A have not been clarified.…”

“…In a previous study, we demonstrated that target molecule(s) of Con A mainly localized on the conjugation papillae during conjugation processes in the C. psl. complex ( Hori et al, 2012 ). To monitor the developmental changes on conjugation papillae, Calcofluor White, which stains β- D -glucopyranose polysaccharides in cell walls, was used as a vital staining reagent.…”

“…Generally, carbohydrate plays important roles in biological organization on the cell surface and cell-cell recognition phenomena. Hori et al (2012) examined whether some lectins affected the conjugation processes of the C. psl. complex.…”

“…complex. Hori et al (2012) reported that fluorescein isothiocyanate (FITC)-labeled Con A weekly bound to the surface of vegetative and nitrogen-deprived cells, however, binding of FITC-labeled Con A at conjugation papillae is quite remarkable and the addition of Con A completely inhibited zygote formation, indicating binding molecule(s) of Con A localized on the conjugation papillae is specifically involved in zygote formation and plays important roles during the process of conjugation in the C. psl. complex.…”

Sexual Reproduction of a Unicellular Charophycean Alga, Closterium peracerosum-strogosum-littorale Complex

“…Information concerning physical cell-cell recognition and fusion of cells involved in conjugation processes has not yet been clarifi ed; however, fl uorescein isothiocyanate (FITC)-labeled lectins, Lycopersicon esculentum lectin (LEL) and Concanavalin A (ConA), accumulated on the conjugation papillae and inhibited the progress of zygote formation (Hori et al 2012 ). These results suggest that different carbohydrates specifi cally recognized by these lectins are involved in cell recognition or fusion during conjugation processes in the C. psl.…”