Regeneration of Vitamin A Deficient Rat Tracheal Epithelium After Mild Mechanical Injury

Mild mechanical abrasion of tracheal epithelium of Vitamin A deficient rats removed the superficial cells and spared basal cells which divided to repopulate the damaged area. The proliferative cells passed through a period of DNA synthesis with the greatest numbers of thymidine incorporating cells in samples labelled 22 h after injury. A peak of cell division occurred at 32 h and there was no further DNA synthesis or cell division. The area of wounding exhibited squamous metaplasia while normal pseudostratified muco-ciliary structure was retained by adjacent epithelium which had not been injured. The data indicates that squamous metaplasia in the respiratory epithelium in longstanding Vitamin A deficiency is due to redirected differentiation of basal cells and is seen only after mitotic activity has occurred.     

Macromolecules in brachiopod shells: characterization and diagenesis

An immunological investigation was conducted of soluble intra-crystalline macromolecules isolated from living and fossil brachiopod shells, which had previously been used for an immunologically based study of phylogeny (serotaxonomy). The soluble intra-crystalline macromolecules comprised 0.03% by weight of the extant shell material. Bulk analysis and gel electrophoresis indicated that the organic material is predominantly glycoprotein, and contains up to 30% by weight carbohydrate. Treatment of the macromolecules with periodate and proteinase K revealed that antibodies were raised predominantly against the carbohydrate moieties. Using a specially adapted dot blot immunobinding assay (DIBA) the decay in immunological signal over geological time was determined. Pleistocene shells have lost between 99 and 99.9% of immunological reactivity, and original antigenic determinants form a declining proportion of total organic matter. It is suggested that condensation reactions between amino acids and sugars account for the rapid destruction of determinants; this has important implications for the direction of future studies on fossil macromolecules. □ Serotaxonomy, biomolecular palaeontology, glycoproteins, melanoidins, brachiopods.     

Encephalitozoon cuniculi: Light and Electron Microscopic Evidence for Di-, Tetra-, and Octosporous Sporogony and a Note on the Molecular Phylogeny of Encephalitozoonidae

We demonstrate, based on the light, electron microscopic, and immunofluorescence studies carried out on two isolates of Encephalitozoon cuniculi established in culture, that E. cuniculi exhibits di-, tri-, tetra- and octosporous sporogony. We therefore propose that the generic characters of Encephalitozoon should be amended to include tetra-sporous sporogony as generic features. Additionally, the molecular phylogenetic analysis indicates that E. cuniculi, E. hellem, and E. (Septata) intestinalis form a cohesive group.     

The Strategy of Carbon Utilization in Uniculm Barley: II. THE EFFECT OF CONTINUOUS LIGHT AND CONTINUOUS DARK TREATMENTS

After a photoperiod of 8.25 h during which the youngest fullyexpanded leaf of uniculm barley plants was allowed to assimilate¹⁴CO₂ for 30 min, groups of plants were transfered either tocontinuous light or to continuous dark. Plants were harvestedover a 72 h period to examine the effect of the treatments (comparedwith control plants growing in normal light/dark cycles) onthe transport of ¹⁴C from the exposed leaf, the distributionof ¹⁴C assimilates to the rest of the plant, and the chemicalfate of assimilated ¹⁴C. In continuous light a substantial quantity (22% at 72 h) ofthe ¹⁴C assimilated by the leaf remained in that leaf in theform of starch and neutral sugars compared with only 4% in thecontrol fed leaf. Also the total amount of ¹⁴C respired fromplants maintained in continuous light was significantly less(c. 18% of the total originally fixed by 24 h) than that respiredfrom control plants (c. 36%). The result was that approximatelyequal amounts of ¹⁴C were accumulated in the growing leavesand roots of plants given continuous light or normal light/darkcycles. In continuous dark the fate of ¹⁴C was similar to that of controlplants. This is probably because the two treatments shared acommon light/dark environment for the first 22 h, during whichtime almost complete distribution and utilization of ¹⁴C occurred.     

Calcium Antagonist TMB-8 Inhibits Cell Wall Formation and Growth in Pea

The effects on auxin-stimulated growth and cell wall formationof 8-(N, N-diethylamino)-octyl-3, 4, 5-trimethoxybenzoate.HCI(TMB-8), an intracellular Ca²⁺ antagonist, were investigatedin abraded stem segments from aetiolated seedlings of Pisumsativum L. cv. Alaska. Incubation of segments at pH 6.0 with200 mmol m^–3 TMB-8 resulted in a 50% inhibition of auxin-stimulatedgrowth. Added Ca²⁺ did not restore normal auxin-stimulated growth,presumably because of its well-known stiffening effect on thecell wall. In segments incubated at a pH (7–2) which preventedelongation, auxin promoted the incorporation of [³H]glucoseinto the cell wall relative to total uptake of label. TMB-8abolished about 60% of the total incorporation of label intocell walls in the presence of auxin, but was not effective inthe absence of auxin. Exogenous CaCl₂ reversed the inhibitoryeffect of TMB-8 on relative cell wall incorporation in a parabolicmanner, with a 50% reversal at about 100 mmol m^–3 andcomplete reversal at 1.0 mol m^–3 Ca²⁺. Other ions tested(Mg²⁺, Mn²⁺, Cu²⁺, Zn²⁺) were without substantial effect atconcentrations of 0.5 mol m^–3. Both apparent uptake ofCa²⁺ and consequent reversal of TMB-8 inhibition of cell wallincorporation were blocked by the Ca²⁺ channel blockers verapamiland La³⁺. The data provide further evidence that auxin-stimulatedgrowth is dependent upon continued cell wall incorporation,and suggest that a Ca²⁺ messenger system may be involved inthe promotory actions of auxin on cell wall synthesis and long-termgrowth. Key words: Auxin, calcium, cell wall synthesis