Singhamoeba horticola (Singh & Hanumaiah, 1979) N. Comb., Type Species of Singhamoeba N. G.

ABSTRACT. Small cyst-forming amoebae described as Schizopyrenus horticolus Singh & Hanumaiah, 1979, were cultured from sediment samples taken from three sites along the Chester River, Kent County, MD. Morphological studies on cysts and trophozoites showed sufficient differences between Sch. horticolus and the type species, Sch. russelli Singh, 1952, to justify its removal from that genus. A new genus, Singhamoeba is proposed to accommodate the species horticolus .     

Trichomonas vaginalis: Dominant G2 Period and G2 Phase Arrest in a Representative of an Early Branching Eukaryotic Lineage

ABSTRACT. Eukaryotic mitotic cell cycles have been extensively studied in yeasts and vertebrate cells but little is known about cell cycle mechanisms in early branches of the eukaryotic lineage. Trichomonas vaginalis represents one of the earliest branching eukaryotic lineages available for study. In contrast with most yeasts and vertebrate cells, the T. vaginalis G2 period was prolonged, comprising 50 to 58% of the cell population. Hydroxyurea, aphidicolin, and excess thymidine, all of which arrest yeasts and vertebrate cells at the G1/S phase boundary, had no effect on the T. vaginalis cell cycle, probably due to the known absence of synthetic pathways. The antimicrotubule mitotic inhibitors, colchicine and nocodazole, induced G2 phase synchrony. Metronidazole, a therapeutic reagent, also caused G2 phase arrest. These observations suggest that T. vaginalis is similar to yeasts and vertebrate cells in G2 and M phases, but the parasite's G1/S phase transition is distinctive. The results also suggest potentially therapeutic, anti-trichomonad activity of microtubule inhibitors such as nocodazole. The cultured parasite may prove useful as a model for the mitotic cell cycle in the absence of G1/S phase transitional activities universal in yeasts and vertebrate cells.     

A new genus and species of Braconinae from Australia (Insecta, Hymenoptera, Braconidae)

Euurobraconoides gen.n. (type-species: Euurobraconoides longicaudis sp.n.) from Australia is described and illustrated. The relationships of Euurobraconoides gen.n. to the Euurobraconini Ashmead and to the Braconini are discussed.     

Learning in Stentor

SYNOPSIS. When placed in a vertical capillary tube of 0.5 mm inner diameter opening at the bottom end into a reservoir, Stentor coeruleus learns to escape; that is, on the 1st trial it takes a long time to find its way out and much less time on the 2nd and succeeding trials. It was found that learning did not occur in a horizontal tube, or in a vertical tube with the open end above, or in tubes of 1 or 2 mm inner diameter. To explain the results it is suggested that the response is actually a delayed geotaxis released only after a definite period of mechanical stimulation from bumping into the walls of the tube. Possibly the phenomenon is related to the process of habituation to mechanical stimuli which has been elucidated by other authors.     

Aminotransferase and the Production of Alanine During Hyperosmotic Stress in Paramecium calkinsi

When Paramecium calkinsi encounter hyperosmotic stress, intracellular free alanine increases. In vivo assays indicate that the reaction catalyzed by alanine aminotransferase contributes to the build up of alanine in response to hyperosmotic shock. ¹⁴C-pyruvate is converted to ¹⁴C-alanine in cells grown axenically at 200 mosm. When shifted to 600 mosm, the rate of conversion of pyruvate to alanine increases, and conversion at either 200 or 600 mosm is blocked by 1 mM aminooxyacetic acid (AOA), an inhibitor of aminotransferase. Intracellular free alanine increase is partially inhibited by AOA, and AOA prevents cells living in fresh water from acclimating to higher salinities, an indication that the increase in intracellular alanine is physiologically significant.     

Four new genera of the PIesiobracon Cameron group (Insecta, Hymenoptera, Braconinae)

Crinibracon gen.n. (type species: Crinibracon malayensis sp.n. from Malaysia), C. indicus sp.n. from India, C. striatus sp.n. from New Guinea, Lyricibracon gen.n. (type species: Lyricibracon bicolorus sp.n. from Brunei), Rugosibracon gen.n. (type species: Rugosibracon maculithorax sp.n. from S. Africa), R. nigerianus sp.n. from Nigeria and Simplicibracon gen.n. (type species: Simplicibracon maculigaster sp.n. from Taiwan) are described and illustrated. A key to the Plesibracon group of genera is provided, together with specific keys for the new genera Crinibracon and Rugosibracon .