Involvement of contractile elements in control of bioluminescence in Northern krill, <Emphasis Type="Italic">Meganyctiphanes norvegica</Emphasis> (M. Sars)

Inside the light organs of the bioluminescent (light-producing) crustacean Meganyctiphanes norvegica (krill), numerous capillaries drain haemolymph into the light-producing structure (lantern). We have investigated the arrangement and function of filamentous material found around the opening of the capillaries. These have been suggested to work as sphincters, controlling the haemolymph (i.e. oxygen) supply to the lantern and thereby the production of light. Electron microscopy shows that the filamentous material consists of thick and thin muscle filaments arranged in perpendicular blocks around the opening of each capillary. The actin probe rhodamine phalloidin has revealed that one component is filamentous actin. Clusters of vesicle-dense nerve profiles surround the cells containing filamentous material and antibodies against 5-hydroxytryptamine (5-HT) reveal that 5-HT containing nerves lead to the filamentous area. When exposed to the muscle-relaxing substances papaverine and verapamil, krill respond with luminescence, suggesting that the sphincter structures are functionally involved in the control of light production. Treatment with the muscle-contracting drugs Bay K8544 and thapsigargin gives no light response. Thus, 5-HT stimulates light production in krill; however, a combination of 5-HT and the muscle-relaxing drugs or Bay K8544 potentiates the effect of 5-HT. Thapsigargin quenches the response to 5-HT. Our results corroborate speculations of earlier authors who have suggested that the sphincter structures are of a muscular nature and important in controlling light production in krill. However, other parameters in addition to the oxygen supply to the lantern are involved in controlling bioluminescence in the light organs of M. norvegica. We acknowledge financial support from the Biodiversity Program of the Swedish Science Research Council and from the Royal Swedish Academy of Science for supporting work at the Kristineberg Marine Research Center. Electron microscopy equipment was granted by the Lundberg Research Foundation.     

Fruit micromorphology and anatomy of Valeriana officinalis s. str. (Valerianaceae)

Fruits of two varieties of Valeriana officinalis s. str. (var. officinalis , var. nitida ) are similar in general construction, but differ in details of external and internal structure. The outer cells of the pericarp form a regularly punctuated surface in both taxa. Scanning electron microscopy demonstrates variation in cuticular sculpturing of the outer epidermal cell walls and the presence of epicuticular wax. The surface of fruit hairs varies from micropapillate in var. officinalis to linear warty in var. nitida . In the mature rericarp there occur three distinct histological zones: an outer exocarp, a central mesocarp, and an inner endocarp. The seed is small, enclosed in the indehiscent fruit, with thin seed coat and a straight embryo. Endosperm is absent. The results of this carpological study, especially the SEM characters of pericarp surface, may provide criteria useful for delimitation of V officinalis varieties.     

Metabolic quenching of <Emphasis Type="Italic">Corynebacterium glutamicum</Emphasis>: efficiency of methods and impact of cold shock

Representative and valid cytoplasmic concentrations are essential for ensuring the significance of results in the field of metabolome analysis. One of the most crucial points in this respect is the sampling itself. A rapid and sudden stopping of the metabolism on a timescale that is much faster than the conversion rates of investigated metabolites is worthwhile. This can be achieved by applying of cold methanol quenching combined with reproducible, fast, and automated sampling. Unfortunately, quenching the metabolism by a sharp temperature shift leads to what is known as cold shock or the cell-leakage effect. In the present work, we applied a microstructure heat exchanger to analyze the cold shock effect using Corynebacterium glutamicum as a model microorganism. Using this apparatus together with a silicon pipe, it was possible to assay the leakage effect on a timescale starting at 1 s after cooling cell suspension. The high turnover rates not only require a rapid quenching technique, but also the correct application. Moreover, we succeeded in showing that even when the required appropriate setup of methanol quenching is not used, the metabolism is not stopped within the required timescale. By applying robust techniques like rapid sampling in combination with reproducible sample processing, we ensured fast and reliable metabolic inactivation during all steps.     

Ureolytic activity of Nitellopsis obtusa (Characeae)

The decomposition of urea by Nitellopsis obtusa from Characeae was investigated. The intact cells were exposed to the inhibition by two typical urease inhibitors: boric acid and fluoride ion, used as a criterion to define if urease or UAL-ase is responsible for the ureolytic activity of the algae. It was found that boric acid and fluoride ion are simple competitive and slow-binding competitive inhibitors of Nitellopsis obtusa enzyme respectively, which is the response characteristic of urease. The inhibition constants equal to 2.3 and 0.1 mM for boric acid and fluoride ion, when compared to those of jack bean urease, indicate that in the observed kinetic behaviour of Nitellopsis obtusa urease partake transport processes taking place in the intact cells.     

Linear Discriminant Functions for Stationary Time Series

Optimal classification rules based on linear functions which maximize the Chernoff distance, or the Morisita distance, or the Kullback-Leibler distance are studied here. We obtain an expression for the optimal linear discriminant function and show that the resulting linear procedure belongs to the Anderson-Bahadur admissible class. For the comparison of discriminant rules we use some index which is the measure of the accuracy of a given class of discriminant procedures. The asymptotic form of the discriminant function is also studied.     

A P-glycoprotein homologue of Plasmodium falciparum is localized on the digestive vacuole

Resistance to chloroquine in Plasmodium falciparum bears a striking similarity to the multi-drug resistance (MDR) phenotype of mammalian tumor cells which is mediated by overexpression of P-glycoprotein. We show here that the P. falciparum homologue of the P-glycoprotein (Pgh1) is a 160,000-D protein that is expressed throughout the asexual erythrocytic life cycle of the parasite. Quantitative immunoblotting analysis has shown that the protein is expressed at approximately equal levels in chloroquine resistant and sensitive isolates suggesting that overexpression of Pgh1 is not essential for chloroquine resistance. The chloroquine-resistant cloned line FAC8 however, does express approximately threefold more Pgh1 protein than other isolates which is most likely because of the increased pfmdr1 gene copy number present in this isolate. Immunofluorescence and immunoelectron microscopy has demonstrated that Pgh1 is localized on the membrane of the digestive vacuole of mature parasites. This subcellular localization suggests that Pgh1 may modulate intracellular chloroquine concentrations and has important implications for the normal physiological function of this protein.