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A new widespread myxomycete species, Physarum pseudonotabile, inhabiting the arid regions of the Eurasia, South and North America is described and illustrated. Tentatively assigned to Ph. notabile T. Macbr., a phylogeny based on the small ribosomal subunit (SSU) and elongation factor 1 alpha (EF1a) genes placed the new species in a clade far from Ph. notabile. Ph. pseudonotabile was found to be frequent in surveys based on the moist chamber culture technique with samples of litter, bark and herbivore dung collected in dry steppe and deserts of the Caspian lowland (Russia), Kazakhstan, Mongolia, China, Spain, Argentina and USA. The main morphological difference between Ph. pseudonotabile and Ph. notabile lies in spore ornamentation. Spores of the former species display irregularly distributed verrucae, whereas the latter species possesses spores with dense and regularly arranged spinulae. In addition, the ecological preferences of the two species differ. Ph. pseudonotabile inhabits the bark of living plants and ground litter in arid regions, whereas Ph. notabile is found on coarse woody debris in boreal and temperate forests. Although the new species appears to be closest to Ph. notabile morphologically, the phylogenetic analysis reveals Ph. pusillum and Ph. nivale as the closest relatives. In addition, the molecular investigations revealed a considerable amount of hidden diversity within species of Physarum with gray lime flakes. Currently we have only sufficient material to assess the morphological variation of Ph. pseudonotabile but expect that more taxa within this clade may emerge within studies combining morphological and molecular analyses.

A new nivicolous species of Physarum was discovered during the study of myxomycetes in the Patagonian Andes of South America. It is described herein under the name Physarum andinum. The species is characterized by stalked sporophores or more rarely sessile sporocarps or short plasmodiocarps. The sporocarps are strikingly large, reaching 2.6 mm tall and 3 mm diam when open, and have a peridium with three layers, the internal layer being clearly visible and opening separately. Physarum andinum was found at five localities in Argentina as well as in herbarium material collected about 100 y ago in Chile. The new species is reminiscent of the non-nivicolous species Physarum brunneolum, but the latter forms smaller sporophores, has darker spores and the three layers of the peridium are adhered and open together. The characters of the new species were examined under stereomicroscope, light microscope and scanning electron microscope and micrographs of relevant details are included.

Myxomycetes are protists whose life cycle depends on aerially dispersed spores that germinate into motile myxamoebae, which then pair and fuse to form a larger, motile plasmodium. The plasmodium seeks out a suitable fruiting site (usually atop vegetative material or detritus) and transforms into fruiting bodies that release the spores. In this paper we report the first known instance of a myxomycete, in this case Physarum pusillum, sporulating on the body of a living animal, the cryptic lizard Corytophanes cristatus, which was collected in eastern Honduras in 2003.

A subcloned portion of the 5' nontranslated sequence from a Physarum alpha-tubulin cDNA is specific for a single alpha-tubulin locus, altB, of Physarum polycephalum. We find that this locus is expressed only in the plasmodium and encodes at least an alpha 1-tubulin isotype, which we have designated alpha 1B. Hybridization patterns of other subclones of this cDNA reveal two sequences for alpha-tubulin at the altB locus.

We have begun a series of studies designed to characterize gene expression during differentiation in the slime mold Physarum polycephalum. This work concerns the starvation phase of the sporulation sequence and describes some of the quantitative changes which occur in plasmodial constituents during the 3-day starvation period and also describes alterations in the transfer ribonucleic acid (tRNA) population. The results show that whereas the plasmodial tRNA content decreased by 75% during starvation, concurrent de novo synthesis of tRNA also occurred, and they also show that overall amino acid acceptor activity of the starvation-phase tRNA population did not differ significantly from that found in the growth phase. Of the 19 starvation-phase tRNA families assayed, however, 6 were found to have consistently lower acceptor activities than did their growth-phase counterparts. Reverse-phase (RPC-5) chromatographic analysis of five of those families failed to reveal any major differences between growth- and starvation-phase isoacceptors. The data suggest that the depletion and resynthesis of tRNA during the starvation phase results in a quantitative alteration in the composition of the tRNA population and that the alteration is tRNA family and not tRNA isoacceptor specific.

Cellular levels of diadenosine tetraphosphate (Ap4A) and adenosine tetraphospho-guanosine (Ap4G) were specifically measured during the cell cycle of Physarum polycephalum by a high-pressure liquid chromatographic method. Ap4A was also measured indirectly by a coupled phosphodiesterase-luciferase assay. No cell cycle-specific changes in either Ap4A or Ap4G were detected in experiments involving different methods of assay, different strains of P. polycephalum, or different methods of fixation of macroplasmodia. Our results on Ap4A are in contrast with those reported previously (C. Weinmann-Dorsch, G. Pierron, R. Wick, H. Sauer, and F. Grummt, Exp. Cell Res. 155:171-177, 1984). Weinmann-Dorsch et al. reported an 8- to 30-fold increase in Ap4A in early S phase in P. polycephalum, as measured by the phosphodiesterase-luciferase assay. We also measured levels of Ap4A, Ap4G, and ATP in macroplasmodia treated with 0.1 mM dinitrophenol. Ap4A and Ap4G transiently increased three- to sevenfold after 1 h and then decreased concomitantly with an 80% decrease in the level of ATP after 2 h in the presence of dinitrophenol. These results do not support the hypothesis that Ap4A is a positive pleiotypic activator that modulates DNA replication, but they are consistent with the hypothesis proposed for procaryotes that Ap4A and Ap4G are signal nucleotides or alarmones of oxidative stress (B.R. Bochner, P.C. Lee, S.W. Wilson, C.W. Cutler, and B.N. Ames, Cell 37:225-232, 1984).

Physarum myxamoebae can be reversibly induced to become flagellates. Physarum flagellates contain a new form of tubulin, alpha 3, that is not found in nonflagellated cells. Evidence is presented that suggests that alpha 3 tubulin arises through posttranslational modification of a preexisting alpha tubulin. Pulse-chase experiments showed that labeled alpha 3 tubulin could be detected when flagellates formed after a chase. RNA was isolated from myxamoebae at different times after induction of flagellum formation. When this RNA was translated in vitro, the resulting products contained no alpha 3 tubulin, also consistent with alpha 3 being made by posttranslational modification. Levels of alpha and beta tubulin RNA increased with the proportion of flagellates in the culture. These elevated tubulin RNA levels declined after the number of flagellates in the population achieved plateau values.