Mutants with continuous microcycle conidiation in the filamentous fungus Fusarium solani f. sp. pisi

Summary A method of repeated mutation induction and subsequent selection was used to obtain mutants with microcycle conidiation, mc, in Fusarium solani f. sp. pisi. Wild-type, wt, Fusarium has a filamentous (hyphal) growth in a three-stage, conidium—hypha—conidiophore (phialid) vegetative life cycle. The first major mutation induced (by means of the mutagen MNNG) changed the wild-type strain 1–3^- from producing both macro- and microconidia to the mutant strain 19-P2^-, producing only microconidia but preserving the three-stage life cycle. When strain 19-P2^- was exposed to a similar mutagenic treatment mutants without the hyphal stage were obtained. In these mutants the microconidia germinate to form phialids directly, which in turn produce new conidia, thus accomplishing the life cycle as a two-stage, conidium-conidiophore, microcycle. The mc mutants were stabilized after reisolation through back-crossing to the wt of complementary mating type. Mc growth of the mutants is continuous under stable conditions, proceeding uninterrupted to the stationary stage in liquid as well as on solid medium. Mc colonies on solid medium are small and soft, well suited to replication by means of velvet or paper. Large numbers of mature, synchronized conidia are easily obtained from stationary-stage submerged cultures. Sequential mutations are of interest for studies of morphogenetic evolution. The ahyphal mutants make this group of eukaryotes well suited for genetic engineering and biotechnology.     

How signal sequences maintain cleavage specificity

The specificity of the signal sequence cleavage reaction has been postulated to reside in a signal peptidase active site that can bind only to particular (i, i + 2) pairs of amino acids. In this paper, we present further patterns of non-random amino acid utilization in a region around in vivo cleavage sites, and show that they can be interpreted in terms of selection acting to reduce the number of potential competing sites in the vicinity of the correct one.     

Characterization and physiological variation of estrogen receptors in rabbit corpora lutea throughout pregnancy and pseudopregnancy: the effect of hysterectomy and sustained estradiol treatment

Previous studies suggest that regression of the rabbit corpus luteum is associated with a uterine-induced loss of responsiveness to estradiol. To determine if this is due to loss of estrogen receptor, cytoplasmic and nuclear estrogen receptors were measured in pseudopregnant, hysterectomized-pseudopregnant and pregnant rabbits throughout luteal life. Estrogen receptor levels were higher in corpora lutea than in nonluteal tissue and were generally higher in nuclei compared to cytosol. Estrogen receptor levels were low on Day 3, increased 2- to 3-fold by Day 6-8, reached peak levels by Days 8-10, and then gradually decreased in a pattern similar to the pattern of serum progesterone typical of each group. Hysterectomy was not associated with elevated cytoplasmic or nuclear estradiol receptor levels. When hysterectomized rabbits were treated with estradiol-filled Silastic implant on Day 1, nuclear estradiol receptor levels fell by Day 20 to levels seen in untreated hysterectomized rabbits. Despite substantial losses in nuclear estrogen receptor, serum progesterone remained elevated on Days 16 and 20. Thus, the ability of estradiol to maintain serum progesterone in hysterectomized rabbits did not correlate directly with the level of estrogen receptor.     

Recovery of proteins on a milligram scale from polyacrylamide electrophoresis gels,exemplified by purification of a retinol-binding protein

An apparatus suitable for the recovery of proteins from polyacrylamide gels on a milligram scale by displacement electrophoresis (isotachophoresis) is described along with a buffer system that is suitable for this purpose with most proteins. The technique is illustrated by the recovery of a protein from a 15% polyacrylamide gel. The recovery was almost quantitative and the eluted protein showed little contamination upon quantitative amino acid analysis and automatic Edman degradation.     

Community patterns of nectivorous adult parasitoids (Diptera,Bombyliidae) on their resources

Summary Highly diverse assemblages of nectivorous bee flies (Diptera: bombyliidae) occur at desert sites in California presenting an opportunity to investigate the ecology of this little-known group. This study compared communities of adult bee flies visiting flowers at two sites, one in the Mojave Desert (Darwin Plateau) and one in the Great Basin (Mono Basin), during periods of higher and lower resource abundance. The range of resources used by single species varied inversely with the number of species present, with the greatest number of species and smallest niche breadths occurring at the Darwin Plateau. Adult bee flies did not visit flower resources at random. Rather the two major divisions of the family exhibited contrasting patterns of specialization on plant species. Results of this study support the hypothesis that resources were limiting for adult bee flies in the period of lower food abundance at the Darwin Plateau and not limiting at the Mono Basin during this study. Bee flies at the Mono Basin exhibited lower densities per flower (despite higher densities per unit area), lower frequency of feeding, a lower degree of specialization, and less pronounced phenological changes than bee flies at the Darwin Plateau. The data suggest that episodes of population regulation in the non-parasitic (i.e. adult) stage, due to short supply of the adults' food, contribute to determining the structure of parasitoid communities.     

The pH Dependency of Relative Ion Permeabilities in the Crayfish Giant Axon

The dependence of the membrane potential on potassium, chloride, and sodium ions, was determined at the pH's of 6.0, 7.5, and 9.0 for the resting and depolarized crayfish ventral nerve cord giant axon. In normal saline (external potassium = 5.4 mM), the dependence of the membrane potential on the external potassium ions decreased with lowered pH while that for chloride increased. In contrast, in the potassium depolarized axon (external potassium = 25 mM), the dependence of the membrane potential on external potassium was minimum around pH 7.5 and increased in either more acidic or basic pH. In addition, the dependence of the membrane potential on external chloride in the depolarized axon was maximum at pH 7.5 and decreased in either more acidic or basic pH. The sodium dependency of the membrane potential was small and relatively unaffected by pH or depolarization. The data are interpreted as indicating a reversible surface membrane protein-phospholipid conformation change which occurs in the transition from the resting to the depolarized axon.     

Buteo albigula Philippi erstmals in Argentinien gefunden

Zusammenfassung In dem großen Hochwaldgebiet, das sich am Fuße der Anden von Jujui bis Orán erstreckt, erbeutete der Verf. am 3. Januar 1969 ein junges Weibchen vonButeo albigula, erster Nach-weis dieser Art aus Argentinien. In dem gleichen Waldkomplex und in annähernd gleicher Höhenlage ist auchButeo brachyurus gesammelt worden. Daraus wird gefolgert, daß diese beiden Bussarde nicht subspezifisch verschieden sind (wieRand urteilte), sondern als zwei Spezies zu gelten haben.

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Sinopsis Una hoven hembra deButeo albigula Philippi fué cazada en Orán del 3 de Energo 1969 por el autor. La especie es nueva para la fauna Argentina. Como la posición sistematica de esta forma era dudosa, el hallazgo es interesante, porque en la misma región ya es conocidaButeo brachyurus Vieillot. La región de las selvas del Noroeste, al pie de los Andes, incluye áreas grandes de bosque humedos, con alturas variables, desde la frontera con Bolivia hasta el sudeste de la provincia de Jujuy. Como ahora las dos formas,albigula y brachyurus son habitantes de la misma región, parecería que son especies y no subespecies.

     

Human arterial smooth muscle cells in culture: Inverse relationship between proliferation and expression of contractile proteins

Summary Human arterial smooth muscle cells (hASMC) from explants of the inner media of uterine arteries were studied in secondary culture. We had previously found that these cells depend on exogenous platelet-derived growth factor (PDGF) for proliferation in vitro. Deprivation of the serum mitogen(s) by culture in plasma-derived serum or bovine serum albumin (BSA) caused a true growth arrest that was reversible upon reexposure to the mitogen(s). When added to serum-containing medium, heparin caused a reversible growth arrest which could be competed for by increasing concentrations of serum. In the current study we used a set of smooth muscle-specific actin and myosin, antibodies to study the expression of contractile proteins in stress fibers under indirect immunofluorescence on hASMC in culture. Even in sparse culture, grwoth-arrested hASMC expressed stress fibers containing these actin and myosin epitopes. This was true irrespective of whether growth arrest was achieved by culture in media containing only BSA or a combination of heparin and whole blood serum. hASMC proliferating in whole blood serum in sparse culture did not express such strees fibers, as judged by immunofluorescent staining. This was true also for cells that were restimulated to proliferate in serum after a growth arrest. Utilizing a monoclonal antibody against a nuclear antigen expressed in proliferating human cells, we were able to demonstrate an inverse relationship between the expression of this antigen and the SMC-specific contractile proteins, respectively. Under these culture conditions, the reversible transition between defifferentiated and differentiated hASMC was almost complete and terminated about 1 wk after the change in culture condition. We conclude that hASMC in vitro respond, to exogenous PDGF by proliferation and dedifferetiation as a single population of cells. We also conclude that this modulation is reversible, because the cells become uniformly quiescent and differentiated when the mitogenic stimulus is blocked or removed. This study was supported by grants from the Swedish Medical Research Council (Project no. 4531 and 6816), the Swedish Association against Heart and Chest Diseases, the King Gustaf V and Queen Victoria Foundation, the National Institutes of Health, Bethesda, MD (grant HL 29873) and the Swedish National Board for Laboratory Animals.