A new ballistosporous species of Protostelium.

During surveys of the protostelids of the Hawaiian Islands and the South Island of New Zealand, an undescribed species of Protostelium was discovered fruiting on collections of substrates found in several sites on the southern and western parts of the island of Hawaii and from one site near Port Elizabeth, New Zealand. The new species, P. okumukumu, has a sporocarp with a bipartite stalk that supports a single, spherical spore. The basal portion of the stalk is straight and rigid. The upper part of the stalk is a nearly spherical apophysis. The junction between the stalk base and the apophysis is flexible such that the spore and apophysis swing back and forth as a unit. Spores are forcibly discharged from the stalk, and only the straight base of the stalk is left behind. Amoebae typical of the taxon Protostelium germinate from the spores, and when an amoeba differentiates into a prespore cell, it becomes lozenge shaped (nearly ellipsoid) in top view, as is typical for species of Protostelium. This represents the seventh species of protostelids described to have forcible spore discharge, and the possibility of forcible discharge needs to be examined in several other species.

Evidence for mating between isolates of Colletotrichum gloeosporioides with different host specificities.

Individual isolates of the ubiquitous plant pathogen Colletotrichum gloeosporioides (teleomorph Glomerella cingulata) can have very restricted host ranges. Isolates that share the same host range are considered to be genetically discrete units, and sexual compatibility has been reported to be limited to individuals that share the same host range. However, we have recently observed that some isolates of C. gloeosporioides that are specifically pathogenic to different, distantly-related hosts are sexually compatible. Ascospore progeny from one such cross were randomly isolated and outcrossing was verified by the reassortment of several RFLP markers among the progeny. In addition, the progeny were analyzed for pathogenicity to parental hosts. The implications of sexual compatibility between C. gloeosporioides isolates with different host specificities on the evolution of Colletotrichum species are discussed.

A proposed phylogeny of the flagellated protostelids.

The flagellated members of the group of mycetozoans known as protostelids have been recognized for some time to be members of a monophyletic group which also includes the myxomycetes. This inference was based primarily upon comparisons of the flagellar apparatus of the amoeboflagellate state. However, more detailed comparisons based on the whole life history and comparisons with an outgroup were necessary to have information sufficient to determine the interrelationships within the group. Recent studies of the other states of the life history of protostelids have provided a wealth of additional morphological and developmental characters such that an in depth phylogenetic analysis is possible. The results show that the group can be resolved into two major clades, one of which contains the myxomycetes and the myxomycete-like protostelid genera, Protosporangium, Clastostelium, and Ceratiomyxa, and another which contains the protostelid genera Planoprotostelium, Cavostelium, and Ceratiomyxella. As the myxomycetes appear to be part of the ingroup, and not a sister group to the protostelids, L.S. Olive's subclass Protostelia must be considered paraphyletic.

Spatial patterns in the fruiting bodies of the cellular slime mold Polysphondylium pallidum.

During morphogenesis in the slime mold Polysphondylium pallidum cell masses are periodically pinched off from the base of the developing sorogen. These masses round up and differentiate into secondary sorogens, which become radially ordered arrays of secondary fruiting bodies called whorls. Here we describe the morphogenesis of P. pallidum and characterize the spacing of whorls along the central stalk of the fruiting body and the spacing of sorocarps within whorls. We find both are highly regular. We propose that the linear spacing of whorls can be accounted for satisfactorily by a model that views the periodic release of cell masses from the base of the developing sorogen as the consequence of an imbalance between forces that orient amoebae toward the tip of the culminating sorogen, and cohesive forces between randomly moving cells in the basal region of the sorogen, which act as a retarding force. The orderly arrangement of fruiting bodies within whorls can be explained most easily by models that employ short-range activation and lateral inhibition.

Obligate amoebae of the protostelids: significance for the concept of Eumycetozoa.

Most flagellate Eumycetozoa have a non-flagellate, or obligately amoeboid, trophic state which differentiates from the amoebo-flagellate state and gives rise to the fruiting body. This study examines the morphology, general ultrastructure, and microtubular systems of the obligate amoebae of three flagellate protostelids with typical amoebo-flagellate states. The obligate amoebae of all three species are morphologically distinct indicating that the obligately amoeboid state has evolved independently in the history of each species. Therefore, obligate amoebae may be useful for defining separate evolutionary groups within the Eumycetozoa.

Phylogenetic significance of the flagellar apparatus in protostelids (Eumycetozoa).

The ultrastructure of the flagellar apparatuses of four species of protostelids is described. All four species have the same three major groups of rootlet microtubules in common, microtubule arrays (MTA) 2, 3, and 4. Variation is found in the number of centrioles per flagellar apparatus, presence or absence of two other microtubule arrays, MTA 1 and MTA 5, types of connectives linking the centrioles to the MTAs, nature of the transitional elements of the flagella, and the association of the flagellar apparatus with the nucleus. It is concluded on the basis of this study and comparison with earlier studies on protostelids, myxomycetes, and other amoeboflagellates that the flagellate species of protostelids are monophyletic. The significance of this to the phylogeny of protostelids and related mycetozoans is discussed.

Roles of actin during sporocarp culmination in the simple mycetozoan Planoprotostelium aurantium.

Developing unicellular fruiting bodies of the protostelid Planoprotostelium aurantium examined by electron microscopy are shown to have a cortical zone of microfilaments that surrounds the lower portion of the sporogenic cell and extends into a cytoplasmic plug that fills the lumen of the tubular, microfibrillar stalk. Labeling with the S-1 fragment of myosin indicates that the microfilaments are actin. A model is proposed in which the actin is involved both in a contractile process that serves to raise the sporogen off the substrate at the tip of the stalk and in a cytoskeletal role by either directly or indirectly localizing the synthesis and orientation of the stalk tube microfibrils. The process of culmination in protostelids is compared to that of the multicellular dictyostelid cellular slime molds.