Mitosis and cytokinesis in Chroomonas africana Meyer & Pienaar (Cryptophyceae)

Mitosis and cytokinesis have been examined in a recently described species of Chroomonas, viz. Chroomonas africana Meyer & Pienaar. A comparison between this species and the three other species in which cell division has been studied (Chroomonas salina and two Cryptomonas spp.) has revealed certain common characteristics such as an open spindle, a chromosomal plate at metaphase and similar types of spindle microtubules with indistinct kinetochores. However, the cell division process in C. africana differs from that in the above mentioned species in that (i) the spindle microtubules maintain their association with the flagellar bases throughout mitosis, (ii) the movement of the chromatin masses at anaphase is synchronous but unequal, i.e. parts of the chromatin masses move at different rates, (iii) in late anaphase and early telophase the chromatin masses arch around the flagellar bases forming cup-shaped structures and (iv) cytokinesis is accomplished by an extension of the anterior vestibular region forming a cleavage furrow which extends posteriorly. The formation of the branched vestibular region is also described. Die mitose en sitokinese van ’n Chroomonas-spesie wat onlangs beskryf is, Chroomonas africana Meyer & Pienaar, is ondersoek. ’n Vergelyking tussen hierdie spesie en die drie ander spesies waarin selverdeling reeds ondersoek is, naamlik Chroomonas salina en Cryptomonas spp. wys op sekere gemeenskaplike eienskappe soos ’n oop spoel, ’n chromosomale plaat tydens metafase en vergelykbare mikrotubuul-tipes met onduidelike kinetochore. Die seldelingsproses in C. africana verskil egter in die volgende opsigte van dié wat in bogenoemde drie spesies voorkom: (i) Die spoel mikrotubule behou dwarsdeur mitose hul assosiasie met die basis van die flagellum, (ii) die beweging van die chromatien-liggame tydens anafase vind gelyktydig maar oneweredig plaas, m.a.w. dele van die chromatienliggame beweeg teen verskillende tempo’s, (iii) gedurende laat anafase en vroeë telofase buig die chromatien-liggame om die flagellum-basis en vorm sodoende koppie-vormige strukture en (iv) sitokinese word deur ’n uitsteeksel van die anterior vestibulêre streek bewerkstellig wat ’n kliewingsinsnoering vorm wat na agter verloop. Die vorming van die vertakte vestibulêre streek word ook beskryf.