Unusual amoebal strains of the MyxomycetePhysarum polycephalum possessing two pro-flagellar apparatuses

Abstract

The microtubules structure of two stable diploid amoebal strains, each resulting from the fusion of two haploid amoebae has been studied by electron microscopy. Tridimensional reconstructions showed that these diploid amoebae-typically possessed two proflagellar apparatuses,i.e., two microtubule organizing centers 1 (mtoc 1) and two pairs of centrioles with their associated microtubular arrays. These observations account for the high frequency of biflagellated amoebae in these two strains. The presence of two mtoc 1 may account for the high percentage of mitotic abnormalities which was observed under phase contrast microscopy and electron microscopy and is in agreement with a role of the mtoc 1 as a mitotic center during mitosis. However, the presence of numerous normal mitotic apparatuses raises the question of the regulations which play a role in the mitotic process. The unusual distribution of centrioles and the unusual pro-flagellar apparatuses which were produced suggest that in interphase the anterior centriole is a necessary structure for the morphogenesis of the microtubular arrays 2 and 3 and that the posterior centriole is a necessary structure for the morphogenesis of the microtubular arrays 4 and 5.