Trypanosoma brucei gambiense and T. b. rhodesiense: Concanavalin A Binding to the Membrane and Flagellar Pocket of Bloodstream and Procyclic Forms1

ABSTRACT We have measured binding of fluorescein-conjugated succinyl-concanavalin A (Fl-s-Con A) to bloodstream and procyclic forms of Trypanosoma brucei gambiense and to bloodstream forms of T. b. rhodesiense by flow cytofluorimetry. Bloodstream forms bound an order of magnitude less lectin than procyclic forms. Trypsin-treating cells enhanced binding of Fl-s-Con A to bloodstream forms 3–16-fold depending on the strain and the length of trypsinization but had little effect on Fl-s-Con A binding by procyclics. The trypsinization protocol used did not remove major common glycoproteins detected on lectin blots of either life cycle form but removed >95% of the variant specific glycoprotein and fragments derived from this protein of bloodstream forms. Microscopically detectable Fl-s-Con A binding to bloodstream forms was confined to the flagellar pocket. Trypsinized bloodstream forms and procyclics bound Fl-s-Con A in the flagellar pocket, on the flagellum, and on the cell surface. Lectin remained cell associated but appeared to redistribute towards the flagellum and pocket when cells that had bound lectin on ice were subsequently incubated at physiological temperatures. The Fl-s-Con A binding had specificity characteristic of the interaction between the lectin and oligosaccharides. These results are consistent with the hypothesis that the variant specific surface glycoprotein blocks binding of the lectin to surface glycoproteins of bloodstream forms and suggest that concanavalin A-binding glycoproteins are abundant in the flagellar pocket of both life cycle forms.     

Impact of a natural enemy overwintering refuge and its interaction with the surrounding landscape

1. Egg parasitoids in the genus Anagrus (Hymenoptera: Mymaridae) are important mortality factors for grape leafhoppers ( Erythroneura elegantula ; Homoptera: Cicadellidae) in California vineyards, yet must overwinter in habitats external to these vineyards. Existing evidence suggests that French prune trees, which harbour the overwintering host Edwardsiana prunicola , planted adjacent to vineyards may enhance early-season abundance of Anagrus.
2. Anagrus overwintering in French prune tree refuges were labelled with the trace element rubidium in four separate experiments. Rubidium-labelled Anagrus were captured in adjacent vineyards in two of the experiments, confirming that French prune trees contribute to early-season Anagrus populations. Anagrus from refuges were captured at the most distant sampling positions, 100 m from refuges.
3. Use of rare element labelling has, for the first time, enabled the relative contribution of different sources to early-season colonization by this parasitoid to be quantified. Refuges contributed 1% and 34% of Anagrus colonizing two of the experimental vineyards, respectively. The remainder originated from overwintering habitats external to the French prune/vineyard system.
4. The spatial patterns of Anagrus originating from external overwintering habitats suggest that the French prune trees are generating a 'windbreak effect'. Anagrus dispersing within the windstream colonized vineyards at a higher-than-average rate immediately downwind of refuges.
5. The amount of colonization by Anagrus from external overwintering habitats was apparently related to the distance to presumed overwintering habitats. These findings demonstrate that both the number of natural enemies emerging from a refuge and the composition of the surrounding landscape are important in determining the impact of local, small-scale habitat manipulations.     

Catchment- and site-scale influences of forest cover and longitudinal forest position on the distribution of a diadromous fish

1. The hydrologic connectivity between landscape elements and streams means that fragmentation of terrestrial habitats could affect the distribution of stream faunas at multiple spatial scales. We investigated how catchment‐ and site‐scale influences, including proportion and position of forest cover within a catchment, and presence of riparian forest cover affected the distribution of a diadromous fish. 2. The occurrence of koaro (Galaxias brevipinnis) in 50‐m stream reaches with either forested or non‐forested riparian margins at 172 sites in 24 catchments on Banks Peninsula, South Island, New Zealand was analysed. Proportions of catchments forested and the dominant position (upland or lowland) of forest within catchments were determined using geographical information system spatial analysis tools. 3. Multivariate analysis of variance indicated forest position and proportion forested at the catchment accounted for the majority of the variation in the overall proportion of sites in a catchment with koaro. 4. Where forest was predominantly in the lower part of the catchments, the presence of riparian cover was important in explaining the proportion of sites with koaro. However, where forest was predominantly in the upper part of the catchment, the effect of riparian forest was not as strong. In the absence of riparian forest cover, no patterns of koaro distribution with respect to catchment forest cover or forest position were detected. 5. These results indicate that landscape elements, such as the proportion and position of catchment forest, operating at catchment‐scales, influence the distribution of diadromous fish but their influence depends on the presence of riparian vegetation, a site‐scale factor.     

Protein Uptake and Digestion in Bloodstream and Culture Forms of Trypanosoma brucei*

SYNOPSIS. The mechanisms of ferritin uptake and digestion differ in bloodstream and culture forms of Trypanosoma brucei. Ferritin enters bloodstream forms from the flagellar pocket by pinocytosis in large spiny-coated vesicles. These vesicles become continuous with straight tubular extensions of a complex, mostly tubular, collecting membrane system where ferritin is concentrated. From the collecting membrane system the tracer enters large digestive vacuoles. Small spiny-coated vesicles, which never contain ferritin, are found in the Golgi region, fusing with the collecting membrane system, and around the flagellar pocket. Acid phosphatase activity is present in some small spiny-coated vesicles which may represent primary lysosomes. This enzymic activity is also found in the flagellar pocket, pinocytotic vesicles, the collecting membrane system, the Golgi (mature face), and digestive vacuoles of bloodstream forms. About 50% of the acid phosphatase activity of blood forms is latent. The remaining nonlatent activity is firmly cell-associated and probably represents activity in the flagellar pocket. The structures involved in ferritin uptake and digestion are larger and more active in the short stumpy than in the long slender bloodstream forms. The short stumpy forms also have more autophagic vacuoles. No pinocytotic large, spiny-coated vesicles or Golgi-derived, small spiny-coated vesicles are seen in culture forms. Ferritin leaves the flagellar pocket of these forms and enters small smooth cisternae located just beneath bulges in the pocket membrane. The tracer then passes through a cisternal collecting membrane network, where it is concentrated, and then into multivesicular bodies. In the culture forms, acid phosphatase activity is localized in the cisternal system, multivesicular bodies, the Golgi (mature face), and small vesicles in the Golgi and cisternal regions. The flagellar pocket has no acid phosphatase activity, and almost all the activity is latent in these forms. The culture forms do not release acid phosphatase into culture medium during 4 days growth. Uptake of ferritin by all forms is almost completely inhibited by low temperature. These differences among the long slender and short stumpy bloodstream forms and culture forms are undoubtedly adaptive and reflect different needs of the parasite in different life cycle stages.     

Thick Filaments in Unstretched Mammalian Smooth Muscle

THE controversy concerning the organization of myosin in mammalian smooth muscle was reviewed (Nature New Biology, 231, 225; 1971) at a time when the studies of Rice's laboratory and our own demonstrated a regular, quasi-rectangular array of thick filaments in guinea-pig taenia coli (TC) and rabbit portal-anterior mesenteric vein (MV), and, further, that, by excessive stretch and by the use of hypertonic incubation solutions, the thick filaments in this lattice could be aggregated into ribbon-like structures^1,2. These observations were made on muscles stretched to approximately 1.5 times their excised length. Both the TC³ and the rabbit MV^2,4 are spontaneously active smooth muscles, which shorten to less than their in vivo length when excised from the body: stretching by approximately 1.5 times brings these muscles close to their in vivo length. Nevertheless, recent reports^5,6, indicating that thick filaments were more readily visualized (but see Figs. 2 and 3 in ref. 5) in stretched smooth muscles, prompted the editorial writer of Nature (231, 423; 1971) to consider it a debatable question whether thick filaments are present in unstretched muscle. Thick filaments have been observed in relaxed muscles^1,5,6 and we now show that an array of thick filaments can also be observed in completely unstretched guinea-pig and rabbit MV smooth muscle (excised and dropped into the fixative) and that such arrays are present after two different modes of fixation.     

The reproductive biology of a distylous tree, Sarcotheca celebica (Oxalidaceae) in Sulawesi, Indonesia

Sarcotheca celebica is a tree endemic lo Sulawesi (and Kabaena Island). Kike many species in the Oxalidaceae it is heterostylous (here distylous). The small red flowers, which last less than one day, are produced in loose inflorescences which bloom over a long flowering season (several months). There are two whorls of stamens in each plant, which overlap in length, perhaps indicating a tristylous origin. Long–styled and short–styled plants differed in the measurements of stamens, styles and pollen grains. Only a small amount of pollen was produced by long–styled plants. Effective insect pollinators were mainly large Hymenoptcra, especially Xylocopa species, which visited many flowers and different trees in rapid succession. A wide diversity of insects visited flowers of both morphs, and numbers visiting each morph were approximately equal. The only successful experimental pollinations were from pollen of short–styled plants onto stigmas of long–styled plants. Automatic self–pollination did not occur. In nature not all flowers produced fruit, some fruits were set with no seeds and a low number of seeds was set in all fruits. The differences in seed set per fruit between short–styled, long–styled and experimental crosses indicate that pollinator visits were insufficient for maximum seed set in some fruits, but selective abortion of seeds must also be occurring. We suggest that S. celebica may represent an intermediate stage in the evolution of dioecy from distyly, with the short–styled flowers making their major genetic contribution through pollen and long–styled flowers through ovules.