Observations of in vitro gametangial copulation and oosporogenesis in Lagenidium giganteum

An in vitro liquid culture oospore production method yielding 5 × 10³ oospores/ml was used to follow the sequential events of gametangial copulation and oospore formation in Lagenidium giganteum. Observations were made with Nomarski differential interference microscopy and scanning electron microscopy. After septation and division of fungal thalli into a chain-like series of links, certain individual subthalli differentiated into gametaniga, oogonia, and antheridia. Antheridia issued a fertilization tube which made contact with, and fused to a single oogonium. Copulative behavior was relatively synchronous and necessitated physical contact between thalli. Sexual reproduction was manifested by the migration and condensation of gametes. Plasmogamy was achieved following the introduction of the male gamete into the oogonium. The fused gametes gave rise to a zygote. Small amounts of periplasm remained in the oogonium. Zygote maturation into a fully developed oospore was characterized by the deposition of a multilaminated oospore wall, the coalescence of lipids into a highly refractive central reserve globule surrounded by a layer of fine-grained cytoplasm.     

Ammonia-assimilating enzymes in bryophytes

Ammonia can be incorporated into amino acids by reductive amination of oxoglutarate, or by the glutamate synthase cycle via glutamine. The majority of plants possess the enzymes necessary for the operation of both these pathways although nitrogen is thought to be assimilated via the glutamate synthase cycle in most cases. Measurements of glutamate dehydrogenase, glutamine synthetase, and glutamate synthase activities are presented from a selection of bryophytes. The genus Sphagnum was found to be unique in lacking measurable glutamate dehydrogenase activity. The relevance of this in the nitrogen-poor acid bog is briefly considered.     

Electron microscopy of gametangial interaction and oospore development in Phytophthora capsici

Gametangial development and oospore formation were studied, with emphasis on cell wall morphogenesis, on mated cultures (A¹xA²) of Phytophthora capsici. In this species, the oogonial and antheridial hyphae interact to produce a typical amphigynous antheridium. The following developmental steps were recognized: 1) contact between oogonial and antheridial initials; 2) penetration of the antheridial initial by the oogonial initial; 3) reemergence of the oogonial initial; 4) oogonial expansion; 5) gametangial delimitation and oogonial wall thickening; 6) penetration of the oogonium by the antheridial fertilization tube; 7) oosphere formation; 8) periplasm degeneration and outer oospore wall formation; and 9) inner oospore wall formation. Electron micrographs were obtained of steps 3–9. Steps 1 and 2 were reconstructed from subsequent events. Steps 3–6 are stages of active wall formation with clear indication of intensive dictyosome activity leading to the formation of numerous wall-destined vesicles of two different sizes and electron densities. No vesicles were seen associated with the development of the inner oospore wall; however, by this stage of development the oosphere cytoplasm exhibited an overall intense electron density that obscured fine detail. Cytoplasmic appearance changed enormously during differentiation, from a developing oogonium rich in mitochondria, ribosomes, rough endoplasmic reticulum, dictyosomes and their vesicles, through an oosphere filled with large finger-print vacuoles and lipid-like bodies, to a mature oospore with a large central vacuole (ooplast) surrounded by a cortex of numerous lipid-like bodies; other organelles are confined to the interstitial space between these storage bodies.     

Regulation of endospore formation in Bacillus subtilis

Spore formation in bacteria poses a number of biological problems of fundamental significance. Asymmetric cell division at the onset of sporulation is a powerful model for studying basic cell-cycle problems, including chromosome segregation and septum formation. Sporulation is one of the best understood examples of cellular development and differentiation. Fascinating problems posed by sporulation include the temporal and spatial control of gene expression, intercellular communication and various aspects of cell morphogenesis.     

Oceanic bryophytes in Atlantic oakwoods

Summary

The oceanic bryophyte element of the vegetation of British and Irish Atlantic oakwoods is not only the richest bryophyte flora in Europe, it is also one of the richest bryophyte floras in the world. The oceanic climate and the buffering provided by the tree canopy are critical in maintaining the constant humidity and equable temperatures which provide the basis for this diversity. Though the initial impression of these woodlands is of a homogeneous green carpet over both rocks and trees, most good woodlands will have over 200 different species of moss and liverwort, many of which are very specific as regards micro-habitat. Within the woodlands, a recently glaciated landscape gives much exposed rock of different aspect, texture and chemistry, and also turbulent burns in deep ravines which enhance the humidity. These niches are exploited by different bryophyte communities which may contain a number of species that are very rare in European terms and for which we have a special responsibility. Any management plans for these woodlands should take account of this variety of micro-habitat, and monitoring of the effects on bryophyte populations of any resulting change in the structure of ground vegetation is vital.     

Comparative inhibitory effects of cytochalasins on the gametangial differentiation inAllomyces arbuscula

In contrast to cytochalasin D which selectively prevents differentiation of female gametangia, cytochalasins A, B and E also masculinizeAllomyces arbuscula by preventing septation between female and male gametangia, thereby allowing the dominant expression of the male characteristics.     

Regulation of new fat cell formation

The formation of new adipocytes occurs either at the stage of multiplication or differentiation or both. It seems possible that the formation of new fat cells is dependent on the average cell weight in a given adipose tissue depot, but there may also be other regional, local regulatory factors. Multiplication of fat cells has been suggested to be stimulated by 17-beta-oestradiol while the differentiation of adipocytes is stimulated by growth hormone, glucocorticoids, insulin, insulin-like growth factor and female sex hormones. There are, probably, other factors acting in circulation or locally. The factors promoting growth of new fat cells with overfeeding are at present unknown. Some hypothetical possibilities are discussed.     

Regulation of nonproteolytic active site formation in plasminogen

Streptokinase may be less effective at saving lives in patients with heart attacks because it explosively generates plasmin in the bloodstream at sites distant from fibrin clots. We hypothesized that this rapid plasmin generation is due to SK's singular capacity to nonproteolytically generate the active protease SK x Pg*, and we examined whether the kringle domains regulate this process. An SK mutant lacking Ile-1 (deltaIle1-SK) does not form SK x Pg*, although it will form complexes with plasmin that can activate plasminogen. When compared to SK, deltaIle1-SK diminished the generation of plasmin in plasma by more than 30-fold, demonstrating that the formation of SK x Pg* plays an important role in SK activity in the blood. The rate of SK x Pg* formation (measured by an active site titrant) was much slower in Glu-Pg, which contains five kringle domains, than in Pg forms containing one kringle (mini-Pg) or no kringles (micro-Pg). In a similar manner, Streptococcus uberis Pg activator (SUPA), an SK-like molecule, generated SUPA x Pg* much slower with bovine Pg than bovine micro-Pg. The velocity of SK x Pg* formation was regulated by agents that influence the conformation of Pg through interactions with the kringle domains. Chloride ions, which maintain the compact Pg conformation, hindered SK x Pg* formation. In contrast, epsilon-aminocaproic acid, fibrin, and fibrinogen, which induce an extended Pg conformation, accelerated the formation of SK x Pg*. In summary, the explosive generation of plasmin in blood or plasma, which diminishes SK's therapeutic effects, is attributable to the formation of SK x Pg*, and this process is governed by kringle domains.     

Regulation of pyrimidine nucleotide formation in Pseudomonas reptilivora

AIMS: To study the regulation of de novo pyrimidine biosynthesis in the pathogenic bacterium Pseudomonas reptilivora ATCC 14836. METHODS AND RESULTS: The pyrimidine biosynthetic pathway enzymes were assayed in extracts of Ps. reptilivora ATCC 14836 cells and of cells from an auxotroph lacking aspartate transcarbamoylase activity. Pyrimidine biosynthetic pathway enzyme activities in ATCC 14836 were influenced by the addition of pyrimidine bases to the culture medium with orotic acid addition inducing dihydroorotase activity. Pyrimidine starvation of the transcarbamoylase mutant strain increased its de novo enzyme activities suggesting that the de novo pathway was also subject to repression by a pyrimidine-related compound. Aspartate transcarbamoylase activity in ATCC 14836 was inhibited in vitro by pyrophosphate and ATP. CONCLUSIONS: Regulation of pyrimidine biosynthesis in Ps. reptilivora was observed at the level of enzyme synthesis and at the level of activity for aspartate transcarbamoylase. Its regulation of enzyme synthesis seemed to be more highly controlled than what was observed in the related species Ps. fluorescens. SIGNIFICANCE AND IMPACT OF THE STUDY: This investigation found that pyrimidine biosynthesis is controlled in Ps. reptilivora. This could prove helpful to future studies exploring its pathogenicity.     

Chromosome studies in some British bryophytes

Abstract

The chromosomes of one moss and thirty liverworts are described and discussed taxonomically. Those of Lepidozia pearsonii (n = 8 + 1m), Telaranea murphyae (n = 9), Leioeolea badensis (n = 8 + 1m), Pleetoeolea paroiea (n = 9), Nardia compressa (n = 8 + 1m), N. geoscyphus (n = 9), Lophoeolea bispinosa (n = 8 + 1m), L. semiteres (n = 8 + 1m), Saccogyna viticulosa (n = 8 + 1m), Scapania curta (n = 16 + 2m), S. compacta (n = 8 + 1m), Porella laevigata (n = 8 + 1m) and P. cordaeana (n = 8 + 1m) are believed not to have been reported previously and, despite references in the literature to the cytology of Riccia crystallina and Gymnocolea inflata, reasons are given for suggesting that the present counts of n = 7 + 1m and n = 8 + 1m, respectively, may also be the first. The remaining species have been recorded cytologically in other parts of the world but not previously for Great Britain, or not with the present karyotype.