Adaptation of a sliding microtome for sectioning of material embedded in epoxy resins]

The employment of a sliding microtome of sectioning plastic embedded material with glass knives is described. Using a new knife holder and a modificated device for fixing plastic blocks succeeded in cutting sections 1--10 micron thick of relatively large pieces of tissue.     

Immunohistological localization and quantification of IAA in studies of root growth regulation

The content and distribution of auxins were studied in gravistimulated roots of maize (Zea mays L.) and primary roots of 7-day-old wheat (Triticum durum Desf.) seedlings, which branching was enhanced by excision of adventitious roots. IAA localization was observed immunohistochemically, using specific anti-IAA antibody in combination with second (anti-species) antibody labeled with colloidal gold. Differences in the IAA content (staining intensity) were found between upper and lower parts of gravistimulated maize roots. We also observed IAA accumulation in the primary wheat root after adventitious root excision; the cells of lateral root primordia were characterized by more intense IAA staining. The role of auxin redistribution in plants for lateral root initiation and development is discussed.     

PICH regulates the abundance and localization of SUMOylated proteins on mitotic chromosomes

Proper chromosome segregation is essential for faithful cell division and if not maintained results in defective cell function caused by the abnormal distribution of genetic information. Polo-like kinase 1–interacting checkpoint helicase (PICH) is a DNA translocase essential for chromosome bridge resolution during mitosis. Its function in resolving chromosome bridges requires both DNA translocase activity and ability to bind chromosomal proteins modified by the small ubiquitin-like modifier (SUMO). However, it is unclear how these activities cooperate to resolve chromosome bridges. Here, we show that PICH specifically disperses SUMO2/3 foci on mitotic chromosomes. This PICH function is apparent toward SUMOylated topoisomerase IIα (TopoIIα) after inhibition of TopoIIα by ICRF-193. Conditional depletion of PICH using the auxin-inducible degron (AID) system resulted in the retention of SUMO2/3-modified chromosomal proteins, including TopoIIα, indicating that PICH functions to reduce the association of these proteins with chromosomes. Replacement of PICH with its translocase-deficient mutants led to increased SUMO2/3 foci on chromosomes, suggesting that the reduction of SUMO2/3 foci requires the remodeling activity of PICH. In vitro assays showed that PICH specifically attenuates SUMOylated TopoIIα activity using its SUMO-binding ability. Taking the results together, we propose a novel function of PICH in remodeling SUMOylated proteins to ensure faithful chromosome segregation.     

Light and electron microscopic study of rat lung brush alveolocytes

The 52 alveolar brush cells (ABC) were revealed in the semi-thin sections of the rat lung tissue, metachromatically stained with toluidine blue. Characteristic features of the ABC on the light microscope level were the following: pyramidal body shape, basal position of the nucleus, darker stain tinge of the cytoplasm than that of other alveolar cells, the presence of microvilli on the small free cell surface. There is one ABC per 21 alveocytes, type 2, and 15 alveocytes, type 1. 41.1% of the ABC are localized in places of adjacent alveolus walls junction, 32.7%--on the alveolus wall facing the alveolus cavity, 16.8%--near the alveolus entrance; 9.4% of the cells are directed into the cavities of two neughbo ring alveoli or settle down near the pores of Kohn. In parallel electron microscopy there was revealed in ABC a form of granular cytoplasmic reticulum (unusual for other alveolocytes) in the form of blocks made up of 5-8 cysternae as if adherent one to another, bundles of filaments and microtubules, vacuoles in the apical cytoplasm. The ultrastructure of ABC, their topography, and incidence in the alveoli of rats evidenced their chemoreceptor nature.     

Gravi- and Chemotropisms of the Primary Maize Roots when Affected by Lead and Cadmium

Gravity-imposed growth orientation was studied in the roots of three-day-old maize seedlings treated for 3 h with 10^–5to 10^–2-M lead and cadmium nitrate solutions. Cubic agar blocks (1 mm³) containing lead and cadmium nitrate solutions were used to produce unilateral local chemostimulation of roots. Gravistimulation was induced when roots were in the horizontal position or slightly deviated from the initial vertical position at the beginning of chemotropic curvature response. Positive (towards the salt) and negative (away from the salt) chemotropic curvatures were observed most often when meristems of the initially vertical roots were chemostimulated. Negative curvatures were observed most often in response to medium salt concentrations, whereas high concentrations resulted in positive curvatures. Half of the roots with their meristems stimulated by salt solutions still continued growing vertically downward. Most roots exposed to simultaneous gravi- and chemostimulation and exposed to gravistimulation after salt treatment (except at the highest salt concentration) curved downward. It follows that the final growth orientation of these roots depended mostly on gravity. The author concludes that the primary roots of maize seedlings possess high gravitropic and low chemotropic sensitivity.     

Ultrastructure of neurons of the myenteric plexus in the normal cat and after temporary circulatory interruption

Ultrastructural organization of neurons in the myenteric plexus of the cat small intestine has been studied in norm and after the blood stream had been switched off for 4 hours and 1, 3, 7, 30 days after recirculation. Ultrastructural uniformity of perikaryons is noted, therefore it is impossible to reveal electron microscopically neurons with different functional qualities. Four morphological types of preterminal dilatations of axons are revealed. Some neurons demonstrate certain resistance to the four hours' ischemia of the intestine, predominance of reactive processes in most of the cells. Dynamics of destructive and reparative processes are followed in neurons and their processes after recirculation.     

Evidence for the Active and Passive Chemotropisms in Roots

Changes in the elongation of root cells during the negative (away from the salt) or positive (towards the salt) chemotropic bending of roots induced by the unilateral application of agar blocks (1 mm³) with 10^–3and 10^–2M Cd(NO₃)₂solutions to the meristem zone of the root were studied. The root bending was not accompanied by differential changes in the number of cells that elongated during the 3-h period of chemical stimulation. The bending was only due to differential changes in the cell elongation rates. In most chemically stimulated roots, both concentrations of Cd(NO₃)₂solutions inhibited cell elongation at the stimulated and nonstimulated sides. Cell elongation was inhibited by 10^–2M Cd(NO₃)₂mainly on the stimulated side of the roots, hence, the roots bent towards the salt. On the contrary, 10^–3M Cd(NO₃)₂inhibited cell elongation mainly at the nonstimulated side of the roots. As a result, the roots bent away from the salt, i.e., in the direction opposite to that expected in the case of the direct inhibition of cell growth by Cd(NO₃)₂. It is concluded that the root chemotropisms induced by the above two Cd(NO₃)₂concentrations are, correspondingly, of a passive or active nature.