A method of rapid examination of meiosis in fruit-trees

Vypracování nové metody rychlého vy?et?ování meiose u jádrového ovoce bylo vynuceno rozsáhlostí materiálu, který bylo nutno zpracovat p?i cytologickém zhodnocení 40 soret ?eskoslovenského základního hru?ňového sortimentu. Metoda umo?ňuje během t?í dn? získat trvalé ?ezané preparáty p?ibli?né z 1800 pra?ník?. Této metody je mo?no pou?ít u v?ech rostlin, které mají v době pr?běhu reduk?ního dělení v pylovýeh mate?ských buěkách dostate?ně velké pra?níky k extirpaci.     

Fine structure of ureteric duct epithelium in the North Atlantic hagfish (Myxine glutinosa L.)

Summary The epithelial cells lining the ureteric duct in the cyclostome, Myxine glutinosa, have a brush border and show specializations of their apical cytoplasm similar to those observed in absorptive proximal tubule cells in higher vertebrate species. These features and the presence of large and numerous cytosomes, presumed to contain lysosomal enzymes, indicate that the ureteric epithelium has taken over some of the functions of the proximal tubule in the atubular kidney of Myxine. Sparsity of basal cytoplasmic processes and mitochondria in the ureteric duct cells appears to correlate with an inability for active, energy-dependent secretory and ion transport functions.This study has been supported by a grant from the Karolinska Institutet Medical School, Stockholm, Sweden (Therese och Johan Anderssons Minne). The author is indebted to Doctor Bertil Swedmark for permission to use the facilities of Kristineberg Marine Biology Station, Fiskebäckskil, Sweden, where hagfish were caught.     

Some features of oscillatory flow in a model bifurcation

Oscillatory flow in the lung is studied using an order-of-magnitude analysis and flow visualization experiments in a single bifurcation with lung-like geometry. The results are used to obtain a classification scheme that identifies three major flow regimes, distinguished on the basis of whether the flow is dominated by unsteadiness, viscous effects, or the effects of convective acceleration. The unsteady regime is found to exist for values of a dimensionless stroke length (L/a, i.e., stroke volume/local cross-sectional area) less than or equal to 3 and for values of a dimensionless frequency (alpha 2 = alpha 2 omega/nu, where alpha is airway radius, omega the oscillatory frequency, and nu the kinematic viscosity) less than or equal to 10 in basic agreement with previous studies. The viscous regime is found when alpha 2(L/a)(a/R)1/2 less than 10 and alpha 2 less than 10 where R is the local radius of curvature in the bifurcation; the convective regime is found when alpha 2(L/a)(a/R)1/2 greater than 10 and L/a greater than 3. This same approach yields scaling laws for the magnitude of secondary flow velocities and shows that the ratio of secondary-to-axial velocity is small everywhere outside of the convective regime where it scales with (a/R)1/2. Comparison of these results to related simple flows shows that many of the features observed can be attributed to the effects of curvature, suggesting that the influence of the flow divider and of area change may be of lesser importance than previously thought.     

Detection and identification ofPodophyllotoxin produced by cell cultures derived from podophyllum hexandrum royle

The phenylpropanoid derived lignan podophyllotoxin, occurring inPodophyllum species, is used as a starting compound for the chemical synthesis of the antitumour agents etoposide (VP-16-213) and teniposide (VM-26). At present, the availability of this lignan becomes increasingly limited. As an alternative source, cell cultures originating fromPodophyllum hexandrum Royle were initiated. Analysis of the cell extracts using different HPLC systems as well as TLC, indicated the presence of podophyllotoxin. After prepurification of the extracts by means of ITLC, the identity was confirmed by mass spectrometric analysis. Dark-grown cultures accumulated considerable higher amounts of podophyllotoxin in comparison with the light-grown cultures.     

Spider toxins selectively block calcium currents in Drosophila

Toxins from spider venom, originally purified for their ability to block synaptic transmission in Drosophila, are potent and specific blockers of Ca2+ currents measured in cultured embryonic Drosophila neurons using the whole-cell, patch-clamp technique. Differential actions of toxins from two species of spiders indicate that different types of Drosophila neuronal Ca2+ currents can be pharmacologically distinguished. Hololena toxin preferentially blocks a non-inactivating component of the current, whereas Plectreurys toxin blocks both inactivating and non-inactivating components. These results suggest that block of a non-inactivating Ca2+ current is sufficient to block neurotransmitter release at Drosophila neuromuscular junction.