A Freeze-Fracture Electron Microscope Study of Trichomonas vaginalis Donné and Tritrichomonas foetus (Riedmüller)1

Two strains of Trichomonas vaginalis, JH162A, with low pathogenicity, and Balt 44, with high pathogenicity, as well as one highly pathogenic strain, KV-1, of Tritrichomonas foetus were studied by freeze-fracture electron microscopy. The protoplasmic faces (PFs) of the cell membranes of all three strains of both species had similar numbers of intramembranous particles (IMPs); however, the particles in the external faces (EFs) of these membranes were least abundant in Trichomonas vaginalis strain Balt 44 and most numerous in those of strain JH162A of this species. In Tritrichomonas foetus strain KV-1 the number of IMPs in the EF was close to but somewhat lower than that in the mild strain of the human urogenital trichomonad. In both species, the anterior, but not the recurrent, flagella had rosette-like formations, consisting of ～9 to 12 IMPs on both the PFs and EFs. The numbers and distribution of the rosettes appeared to vary among different flagella and in different areas of individual flagella of a single organism belonging to either species. The freeze-fracture electron micrographs provided a more complete understanding of the fine structure of undulating membranes of Trichomonadinae, as represented by Trichomonas vaginalis, and of Tritrichomonadinae (the Tritrichomonas augusta-type), as exemplified by Tritrichomonas foetus, than was gained from previous transmission and scanning electron microscope studies. Typically three longitudinal rows of IMPs on the PF of the recurrent flagellum of Trichomonas vaginalis were noted in the area of attachment of this flagellum to the undulating membrane. The functional aspects of the various structures and differences between certain organelles revealed in the two trichomonad species by the freeze-fracture method are discussed.     

Floral development of Bougainvillea spectabilis Willd., Boerhaavia diffusa L. and Mirabilis jalapa L. (Nyctaginaceae)

Three morphological problems were investigated in three species of the Nyctaginaceae: epiphylly, phyllotaxis and placentation. Epiphylly, which occurs in Bougainvillea spectabilis , is the result of ontogenetic displacement resulting from the activity of an intercalary meristem at the base of the floral bract and the floral bud. Floral development of Bougainvillea spectabilis was compared with that of Boerhaavia diffusa and Mirabilis jalapa . Considerable variation occurs with regard to the number and arrangement of stamens. Five stamens are initiated simultaneously, alternate to the petals, in Mirabilis . In Bougainvillea , eight stamens arise sequentially at divergence angles suggestive of a 3/8 spiral. No developmental evidence was found to support the derivation of the eight stamens from a two whorled pentamerous androecium. Boerhaavia normally has only two stamens which most frequently are initiated toward opposite sides of the floral apex, but may also be formed in a 2/5 to 3/8 divergence. In some flowers only one or three stamens are formed. The gynoecium is formed in the same way in all three species: growth occurs in a crescent-shaped zone at the periphery of the floral apex thus producing the gynoecial wall. The single ovule, which is basal in the mature gynoecium, is formed from the gradual upgrowth and transformation of the floral apex and is developmentally terminal. Even the two-layered tunica is maintained as the floral apex is transformed into the ovule primordium. If 'carpel' is defined traditionally as a folded megasporophyll which bears and encloses ovule(s) then carpels are not present in the gynoecia of the three species studied. If 'carpel' is re-defined as an appendage which encloses ovule(s), then the gynoecia of the Nyctaginaceae are carpellate. However, the ovules remain cauline regardless of which definition is adopted.     

Evidence for NADH- and NADPH-linked Glutamate Dehydrogenases in Trypanosoma cruzi Epimastigotes*

SYNOPSIS Two glutamate dehydrogenases, NADH-linked (EC 1.2.1.2) and NADPH-linked (EC 1.2.1.4.) were isolated from the epimastigote forms of Trypanosoma cruzi and purified. Both enzymes exist as hexamers. The molecular weights of the native NADH-and NADPH-linked glutamate dehydrogenases were estimated to be 360,000 and 265,000, respectively, and those of the subunits to be 58,000 and 43,000, respectively. The isoelectric point of the NADH-linked dehydrogenase is at pH 5.25 and that of the NADPH-linked enzyme at pH 5.1. The activities of both enzymes are regulated by product inhibition. In addition, purine nucleotides were shown to be potent inhibitors of the NADH-linked glutamate dehydrogenase.     

The male postabdomen and reproductive system of Bibio marci Linnaeus, 1758 (Hexapoda: Diptera: Bibionidae)

The male postabdomen and the internal parts of the male genital system of Bibio marci (Bibionomorpha) were examined and reconstructed 3‐dimensionally. Several features differ from the presumptive dipteran groundplan. The bases of the gonopods are fused with each other and with tergite IX. The penis is not tube‐shaped and only sclerotized on the ventral side. The vasa deferentia are S‐shaped, and two pairs of accessory glands are present. In contrast to these characteristics, the arrangement of the internal parts is probably close to the ancestral condition. With its specific shape, the penis is well suited for the transfer of a spermatophore. The dorsal sclerite of the copulatory organ probably represents the medially fused parameres. A cladistic analysis of 27 characters of the postabdomen yielded two most parsimonious trees, with the strict consensus as follows: Nannochoristidae (outgroup) + (Culicidae [Culicomorpha] + ((Nymphomyiidae + (Tipulidae + Trichoceridae)) + (Tabanidae [Brachycera] + (Bibionidae, Anisopodidae, Axymyiidae [Bibionomorpha])))). Potential synapomorphies of Bibionomorpha (including Axymyiidae) and Brachycera are the fusion of sternum IX with the gonocoxites, the fusion of the parameres forming the dorsal sclerite and the presence of an entire series of postabdominal muscles (M4, M20, M23, M26, M27, M31, M35 and M37). The results of the analysis are preliminary as it is based on a single‐character system with a limited taxon sampling. However, the main result – a clade Bibionomorpha + Brachycera – is fully compatible with current hypotheses on dipteran phylogeny.     

催化吲哚生成靛蓝的细胞色素P450BM-3 定向进化研究

以催化吲哚产生的靛蓝在 630 nm 处具有特殊的吸收峰为高通量筛选指标,将来源于 Bacillus megaterium 的细胞色素 P450BM-3 单加氧酶的基因序列用易错聚合酶链式反应进行定向进化,通过多轮突变,在原有的能产靛蓝的高活力突变酶的基础上成功获得了三个高于亲本酶的突变酶,突变酶的酶活分别是亲本酶的 6.6 倍 (hml001) , 9.6 倍 (hml002) 和 5.3 倍 (hml003) ,并对突变酶的动力学参数进行了分析 . 突变酶 DNA 测序的结果表明, hml001 含有一个有义氨基酸置换 I39V , hml002 含有三个有义氨基酸置换 D168N , A225V , K440N , hml003 含有一个有义氨基酸置换 E435D ,这些突变位点有些远离底物结合部位,有些位于底物结合部位 .     

Cultivation of Leishmania donovani and Leishmania braziliensis in Defined Media: Nutritional Requirements

SYNOPSIS Nutritional requirements of promastigotes of Leishmania donovani and Leishmania braziliensis were studied in modifications of a simple defined culture medium. "Continuous growth," considered as propagation through 10 successive passages, was supported by inorganic salts, 14 l -amino acids (arginine, cysteine, glutamine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, tryptophan, tyrosine, valine), glucose, adenosine, and a mixture of 11 vitamins and related growth factors. Purified defatted bovine serum albumin proved beneficial. The nutritional needs of the above species of Leishmania differ from those of 2 other hemoflagellate species, Leishmania tarentolae and Crithidia fasciculata , for which glucose, proline and glutamine were found to be nonessential. It is suggested that lower hemoflagellates may be capable of synthesizing these substrates de novo. Leishmania donovani and L. braziliensis required higher levels of folic acid than L. tarentolae , probably due to the fact that folates are involved as cofactors in the biosyntheses of pyrimidines and serine. Although the mixtures reported here cannot be regarded as "minimal essential" media, they are considerably less complex than the ones employed so far for cultivating hemoflagellates, and are therefore well suited for studies related to nutrition and biosynthetic capabilities of Trypanosomatids.     

Cyclic AMP and Calcium in Relaxation in Intestinal Smooth Muscle

WE have studied the role of cyclic AMP in relaxation of smooth muscle and elucidated the mechanism of its action.     

Effect of water availability on leaf water isotopic enrichment in beech seedlings shows limitations of current fractionation models

Current models of leaf water enrichment predict that the differences between isotopic enrichment of water at the site of evaporation (Δ_e) and mean lamina leaf water enrichment (Δ_L) depend on transpiration rates ( E ), modulated by the scaled effective length ( L ) of water isotope movement in the leaf. However, variations in leaf parameters in response to changing environmental conditions might cause changes in the water path and thus L . We measured the diel course of Δ_L for ¹⁸O and ²H in beech seedlings under well-watered and water-limited conditions. We applied evaporative enrichment models of increasing complexity to predict Δ_e and Δ_L, and estimated L from model fits. Water-limited plants showed moderate drought stress, with lower stomatal conductance, E and stem water potential than the control. Despite having double E , the divergence between Δ_e and Δ_L was lower in well-watered than in water-limited plants, and thus, L should have changed to counteract differences in E . Indeed, L was about threefold higher in water-limited plants, regardless of the models used. We conclude that L changes with plant water status far beyond the variations explained by water content and other measured variables, thus limiting the use of current evaporative models under changing environmental conditions.     

Spatially patterned guild structure in larval parasitoids of cyclically outbreaking winter moth populations

1. Wide temporal fluctuations in host abundance are a potential source of instability and stochasticity in the spatiotemporal population dynamics of associated parasitoid species. Within parasitoid guilds (i.e. parasitoids with similar modes of host utilisation), a conceivable outcome is guild organisation according to a lottery model, in which guild members attain local dominance by colonising previously emptied habitats during increasing host density, before other guild members. In the spatial dimension, an expected manifestation of such dynamics is variable guild structure even across homogeneous habitats. 2. We examined the extent of large‐scale spatial patterning of guild characteristics in larval parasitoid wasps associated with cyclically outbreaking populations of the geometrid moth Operophtera brumata in northern Fennoscandia. The study was performed at the onset of the crash‐phase of the geometrid's outbreak cycle, along a 70‐km transect in costal northern Norway, characterised by largely homogeneous environmental conditions, except for a small climatic gradient. 3. There was a distinct large‐scale spatial turnover in dominance among the major parasitoid groups (i.e. guild structure) in O. brumata along the transect, whereas the total prevalence rate of the guild and its diversity showed no consistent variation. Guild structure was unrelated to host density. 4. Although group‐specific responses to a slight spatial climatic gradient cannot be rejected as a causal mechanism, we conclude that our results are consistent with the expectation from large‐scale stochastic extinction‐recolonisation dynamics among functionally equivalent parasitoids relying on a host with strongly cyclic population fluctuations.