Cytochalasin B binding by human platelets

Intact human platelets bind cytochalasin B (CB) with a capacity of 100– 120 p mols CB/mg protein or approximately 7 × 10⁴ molecules/cell and dissociation constants (K_D) ranging from 2 × 10^?8 to 10^?6 M. Up to 85% of this saturable binding is displaced by 10^?5 M cytochalasin E (CE). This CE-sensitive binding also appears heterogeneous with K_D similar to those of the overall binding. The CE-insensitive binding, however, appears as a single component with K_D ≌ 4 × 10^?7 M. The sedimentable constituents from frozen, thawed, and washed cells also bind CB with K_D ranging from 2.4 × 10^?8 to 1.5 × 10^?6 M and a total capacity of approximately 39 p mols/mg protein which accounts for only 4% of the ligand binding to the intact cell. The major portion (60–80%) of this CB binding is displaceable by 500 mM D-glucose and has a K_D of 1.5 × 10^?6M, while only 10–15% is CE-sensitive with a K_D of 2.4 ± 10^?8 M. It is concluded that 95% of the saturable CB binding in platelets is associated with the cytosol of which 80–85% is sensitive to CE and that only 3% of the cellular binding is glucose sensitive, membrane-associated binding. If the CE-sensitive binding associated with the cytosol is entirely to actin, the stoichiometry of this binding is approximately one CB to 30 actin monomers, which is greater by an order of magnitude than that for CB binding to muscle actin.     

Method for growing plants aeroponically

A simple, inexpensive system for growing plants with their roots bathed in nutrient mist is described. The aeroponics system uses a spinner from a home humidifier to propel nutrient solution into a polyethylene-lined plywood box atop which plants are supported on plastic light-fixture “egg crating.” Success in growing a number of herbaceous and woody species, including nodulated legumes and nonlegumes, is reported.     

X-Ray diffraction of oriented amylose fibers. II. Structure of V amyloses

Oriented amylose fibers in the V form were prepared and subjected to x-ray analysis. Unit cells and the probable space group of P2₁2₁2₁ were determined for the V anhydrous and V hydrate forms of amylose; the analysis confirms previous predictions of these structures based on x-ray powder patterns. Chain folding in V amyloses is discussed in view of crystallographic evidence and folding experiments conducted with space-filling models. Reported also is evidence for amylose helices having diameters intermediate between 13.0 and 13.7 A.     

Effects of environment,seedling age,and seed source on leaf resistance of three species of Chamaecyparis and Tsuga chinensis

Summary The objectives of this study were to determine how stomata of Chamaecyparis spp. react to environmental changes and to determine in what ways leaf resistance patterns may have adaptive value for these confers. Leaf resistances were measured of Chamaecyparis taiwanensis, C. formosensis and C. lawsoniana seedlings in a forest nursery, and of saplings of the first two species and Tsuga chinensis growing in natural forest and clearcuts. Light, temperature, humidity, and sometimes xylem pressure potential were measured concurrently.In the nursery, C. lawsoniana, the species from the driest climate, had the lowest resistance, daily means for well-watered yearold plants being 2–5 s cm^-1. Leaf resistances of well-watered C. formosensis and C. taiwanensis from more humid habitats were two and three times greater. Leaf resistance was more sensitive to environment in those nursery populations of C. formosensis from habitats where a dry season is more severe. There were no clear patterns of variation within the other species. Resistance of scale leaves increased with seedling size and age. Primary leaves of C. formosensis had higher average resistance than its scale leaves, and were more responsive to changes in the environment.In the field, C. taiwanensis had higher resistance than C. formosensis. Leaf resistance of Tsuga chinesis was quite similar to that of C. formosensis. Resistance decreased from winter to spring except during a severe dry spell in March.Changes in leaf resistance were most consistently correlated with humidity, which often increased during the day as humid air rose from the lowlands. Stomata opened as humidity rose even when plant xylem pressure potentials were -15 to -23 bars. Stomatal reaction of Chamaecyparis spp. varies in ways apparently adaptive to their environment.     

A whole-system reconsideration of paradigms about photoperiod and temperature control of crop yield

Summary Effects by photoperiod gene(s) and daylength on crop yield and its three major physiological components (aerial biomass, harvest index, and days to harvest maturity) are reviewed for bean (Phaseolus vulgaris L.) and peanut (Arachis hypogaea L.). In these plus many other cited crops, photoperiod sensitive gene(s) delay days to flowering and/or days to maturity in non-promotive daylength while simultaneously lowering the harvest index. Thus, for many crops, earlier maturity is associated with higher harvest index, and/or it has been shown that photoperiod gene(s) control partitioning of photosynthate toward reproductive growth versus toward competitive partitioning to continued vegetative growth. Our conclusion is that photoperiod gene control over this partitioning precedes and is causal of the photoperiodgene control over days to flowering and maturity. This implies shifts from commonly accepted paradigms about effects by photoperiod and about breeding for higher yield. These paradigm shifts suggest more efficient ways to breed for cultivar adaption to the specific growing season duration and environment of each geographical site and for higher crop yield.     

Direct activation of trpl cation channels by G alpha11 subunits.

G proteins of the Gq/11 subfamily functionally couple cell surface receptors to phospholipase C beta (PLC beta) isoforms. Stimulation of PLC beta induces Ca2+ elevation by inositol 1,4,5-trisphosphate (InsP3)-mediated Ca2+ release and store-dependent 'capacitative' Ca2+ entry through Ca(2+)-permeable channels. The Drosophila trp gene, as well as some human trp homologs, code for such store-operated channels. The related trp-like (trpl) gene product also forms a Ca(2+)-permeable cation channel, but is not activated by store depletion. Co-expression of the constitutively active Gq subfamily member G alpha 11 (G alpha 11) with trpl enhanced trpl currents 33-fold in comparison with co-expression of trpl with other G alpha isoforms or G beta gamma complexes. This activation could not be attributed to signals downstream of PLC beta. In particular, InsP3 infusion, modulation of protein kinase C activity or elevation of intracellular calcium concentration failed to induce trpl currents. In contrast, purified G alpha 11 (but not other G protein subunits) activated trpl channels in inside-out patches. We conclude that trpl is regulated by G11 proteins in a membrane-confined manner not involving cytosolic factors. Thus, G proteins of the Gq subfamily may induce Ca2+ entry not only indirectly via store-operated mechanisms but also by directly stimulating cation channels.     

Secondary succession and summer herbivory in a subarctic grassland: community structure and diversity

A field experiment was established in a subarctic grassland in the Finnish Lapland to study the role of summer herbivory in plant community succession Perennial vegetation and moss cover were removed in an area of 324 m² The site was divided into four blocks, of which two were fenced to prevent herbivory by large mammals (reindeer, hare)
Early successional changes in the vegetation were assessed Mean species richness per 3 × 3 m plot was consistently higher in the fenced area, indicating that herbivory can suppress small-scale diversity Herbivory affected the height of several plant species However, there was no correlation between frequency and height of individual species There was a weak indication that taller species were more successful m early succession when grazed Light competition is apparently not a key process determining successional change Thus, in early stage of succession, summer herbivory has little effect on diversity by limiting light competition, and most species are equally successful in grazed and ungrazed plots There was some indirect evidence about competitive interactions in the developing community However, unlike temperate grasslands, large mammal herbivory and competition for light seem not to be important determinants of community change in this subarctic grassland (at least what concernes early successional stages) This may be explained by the harshness of local climate, and abundance of light due to the polar day     

An experimental test of diversity maintenance mechanisms,by a species removal experiment in a species-rich wooded meadow

Most theories of plant species coexistence assume the presence of diversity maintenance mechanisms, i.e. mechanisms enhancing species richness in a community. We wished to determine whether such a mechanism was operating by establishing a field experiment in the species-rich wooded meadow of Laelatu, western Estonia. Ten to seventeen subordinate species were removed periodically (for 4 years) from 10 permanent plots of 1×1 m (each plot had its specific list of excluded species; 10 plots served as control). Since the removed species were all subordinate ones, very little biomass was removed, but at the same time richness was reduced by 25–33%. If some diversity maintenance mechanism was operating, we would expect that immigration of other subordinate species would restore the original species richness. It was not possible to reject the null hypothesis of an identical immigration rate of new species into manipulated and control plots. The rate of small-scale species turnover was not affected by the removal of subordinate species. Interrelations of five richness characteristics were studied, by comparing empirical correlations among them, with those expected from a null model of random migration of species. The immigration rate of new species appeared to be related to the number of constant species, and immigration/extinction balance related to initial richness, more strongly than predicted by the null model. In the manipulated series these relationships matched the expectation from the null model. While the results generally support the so-called species pool hypothesis (and the carousel model), it seems that species small-scale turnover depends on the richness pattern in the studied grassland. In the case of plots with artificially reduced richness no departures can be detected from the random migration hypothesis.     

Novel N-substituted benzimidazole CXCR4 antagonists as potential anti-HIV agents

The lead optimization of a series of N-substituted benzimidazole CXCR4 antagonists is described. Side chain modifications and stereochemical optimization led to substantial improvements in potency and protein shift to afford compounds with low nanomolar anti-HIV activity.     

High diversity of arbuscular mycorrhizal fungi in a boreal herb-rich coniferous forest

* Here, the diversity of arbuscular mycorrhizal (AM) fungi was determined in a boreal herb-rich coniferous forest in relation to environmental variables. * Root samples of five plant species (Fragaria vesca, Galeobdolon luteum, Hepatica nobilis, Oxalis acetosella and Trifolium pratense) were analysed from stands differing in age and forest management intensity. * Thirty-four Glomeromycota taxa (small-subunit ribosomal RNA gene (SSU rDNA) sequence groups) were detected from 90 root samples (911 clones), including eight new taxa. Sequence groups related to Glomus intraradices were most common (MO-G3 and MO-G13). Samples of H. nobilis were colonized by more AM fungal taxa (3.68 +/- 0.31) than those of O. acetosella (2.69 +/- 0.34), but did not differ significantly in this respect from those of F. vesca (3.15 +/- 0.38). Effects of forest management, host plant species (except above) or season on the number or composition of fungal taxa in root samples were not detected, and neither were they explained by environmental variables (vegetation, soil and light conditions). * This is the most taxon-rich habitat described to date in terms of root-colonizing Glomeromycota. The data demonstrate the importance of temperate coniferous forests as habitats for AM fungi and plants. Lack of obvious fungal community patterns suggests more complex effects of biotic and abiotic factors, and possibly no adverse effect of common forest management practices on AM fungal diversity.