Cultivar differences in the rate of nitrate uptake by intact wheat plants as related to growth rate

Six Argentinian wheat ( Triticum aestivum L.) cultivars grown in nutrient solutions in controlled environment were compared for their nitrate uptake rates on a root dry weight basis. Up to 3-fold differences were observed among the cultivars at 16, 20 and 24 days from germination, either when measured by depletion from the nutrient solution in short-term experiments, or by total N accumulation in the tissue during 8 days.
No differences in total N concentration in root or shoots were found among cultivars. Although the different cultivars showed significant differences in shoot/root ratio and nitrate reductase activity (EC 1.6.6.1) in the roots, none of these parameters was correlated with the nitrate uptake rate. However, nitrate uptake was found to be positively correlated (r = 0.99) with the shoot relative growth rate of the cultivars. The three cultivars with the highest nitrate uptake rates and relative growth rates showed a positive correlation between root nitrate concentration and uptake. However, this correlation was not found in the cultivars with the lowest growth and uptake rates.
Our results indicate that the difference in nitrate uptake rate among these cultivars may only be a consequence of their differences in growth rate, and it is suggested that at least two mechanisms regulate nitrate uptake, one working when plant demand is low and another when plant demand is high.     

Uptake and metabolism of benzyladenine in the early stage of flower bud development in vitro in tobacco

Benzyladenine (BA) was found to regulate the number of flower buds regenerated in vitro from pedicel tissue of tobacco. Flower bud induction was particularly sensitive to BA levels in the range of 0.45 to 1.0 μ M , where a two-fold increase in concentration caused a threefold rise in the number of buds. When tissues were fed radioactive BA for 24h, only 9–12% of the counts were recovered in the original compound. The rest was present in metabolites, tentatively identified as the mono-, di- and triribotides, 7- and 9-glucosides and 9-riboside of BA. The amount of growth regulator taken up and the quantities of BA and its metabolites in the explants were all linearly related to the concentration of the medium. The internal BA concentration was ca 60% of the level in the medium after 24 h. When the concentration in the medium was raised, relatively more BA remained in the non-conjugated form. However, this change in the equilibrium between BA and the conjugates is too small to account for the steep rise in the curve representing concentration vs effect between 0.45 and 1.0 μ M .     

Total root length as estimated from small sub-samples

A method is proposed for estimating the total length of a root system from sub-samples. This method is based on the measurement of the length and diameter of small pieces of roots, and on the measurements of the bulk density of root sub-samples. It is assumed that roots are cylinders with a given bulk density. The length and diameter of small root pieces are measured by image analysis. A weighted quadratic mean (W.Q.M.) root diameter is then calculated and used in estimating the root length. This W.Q.M. diameter is defined as the real mean diameter of an equivalent single root with the same length and volume as the tested root system. The accuracy of prediction is demonstrated for one theoretical root system. The standard deviation of estimation can be calculated using sampling simulations.     

Purification and characterization of lymphocytic clonal growth factor (LCGF) derived from human-human hybridoma SH-76 cells

Human-human hybridoma SH-76 cells were found to produce a factor that supported the growth of lymphocytic cells at low densities. The factor was purified from serum-free conditioned medium of the hybridoma cells by a successive application of ammonium sulfate precipitation, DEAE-Toyopearl, TSK G3000 SW and DEAE-5PW column chromatograph. The purified factor was a 72K single protein. The factor showed marked growth stimulating effect on lymphocytic cell lines, but had no effect on the growth of human adhesive cancer cell lines. Thus, the factor is a lymphocytic clonal growth factor (LCGF), as found previously in human plasma (Miyata, 1988). The LCGF of SH-76 cells could be produced in growth factor-free RPMI medium and purified easily from the conditioned medium. The factor is inactivated by heating at over 80°C, but is much more stable than the LCGF in human plasma.     

The structure and cytochemistry of the pistil of Hypericum calycinum: the style

Summary A typical style of Hypericum calycinum is solid with a core of transmitting tissue traversing the whole length of the style. This transmitting tissue consists of loosely arranged cells and large intercellular spaces filled with a secretion product. The secretion product is rich in lipids, but poor in proteins and polysaccharides. The intercellular spaces of the transmitting tissue originate partly by a separation of cells as a result of the decomposition of the middle lamella and partly by degeneration of some of the cells of the transmitting tissue. H. calycinum is self-compatible. Both self- and cross-pollinations result in profuse pollen germination on the stigma and pollen tube growth through the style. The data on Hypericum is discussed in relation to information available on other solidstyled systems.     

Endogenous cholesterol synthesis is sufficient for ACTH-induced differentiation of rat adrenocortical cells in primary culture

Summary To define the role of endogenously synthesized cholesterol in the differentiation of adrenocortical cells in primary culture, fetal rat adrenal cells were cultured in the presence of exogenous cholesterol (serum-supplemented medium) or in the absence of it (serum-free medium or lipoprotein-free medium). Ultrastructurally the cells had features of glomerulosa cells: mitochondria were oval or rod shaped with lamellar inner membranes. The amount of smooth endoplasmic reticulum was small, and lipid droplets were few. When the cells were cultured in serum-free medium some intracytoplasmic vacuoles were seen. The undifferentiated zona glomerulosa-like cells secreted low amounts of corticosterone and 18-OH-deoxycorticosterone (18-OH-DOC) in all three media (serum-supplemented medium, serum-free medium, and lipoprotein-free medium). Stimulation of the adrenocortical cells with ACTH induced the ultrastructural features of differentiated zona fasciculata-like cells. Mitochondrial inner membranes were well developed in lipoprotein-free medium, but not in serum-free medium. The amount of intracellular lipids was increased in both media devoid of cholesterol. In the ACTH stimulated cultures the presence of exogenous cholesterol resulted in increased secretions of corticosterone and 18-OH-DOC. In the absence of an exogenous source of cholesterol, the amounts of steroids secreted were only half of that secreted in the presence of serum-supplemented medium. Endogenously synthesized cholesterol is sufficient for the morphologic differentiation of fetal rat adrenocortical cells under ACTH stimulation. However, without exogenously provided cholesterol, the steroid production accounts only for half of the maximal output achieved using serum-supplemented medium. This work was supported by Finnish Culture Foundation.     

A computerized mechanical cell stimulator for tissue culture: Effects on skeletal muscle organogenesis

Summary A tissue culture system has been developed which can mechanically stimulate cells growing on a highly elastic plastic substratum in a 24-well cell growth chamber. The collagen-coated substratum to which the cells attach and grow in the Mechanical Cell Stimulator (Model I) can be repetitively stretched and relaxed by stepper motor with linear accuracy of 30 μm. The activity controlling unit is an Apple IIe computer interfaced with the cell growth chamber via optical data links and is capable of simulating many of the mechanical activity patterns that cells are subjected to in vivo. Primary avian skeletal myoblasts proliferate and fuse into multinucleated myotubes in this set-up in a manner similar to normal tissue culture dishes. Under static culture conditions, the muscle cells differentiate into networks of myotubes which show little orientation. Growing the proliferating muscle cells on a unidirectional stretching substratum causes the developing myotubes to orient parallel to the direction of movement. In contrast, growing the cells on a substratum undergoing continuous stretch-relaxation cycling orients the developing myotubes perpendicular to the direction of movement. Neither type of mechanical activity significantly affects the rate of cell proliferation of the rate of myoblast fusion into myotubes. These results indicate that during in vivo skeletal muscle organogenesis, when substantial mechanical stresses are placed on skeletal muscle cells by both continuous bone elongation and by spontaneous contractions, only bone elongation plays a significant role in proper fiber orientation for subsequent functional work. Supported by grants NS16753, AR36266, and RR05818 from the National Institutes of Health, Bethesda, MD.     

Preservation of the diffusible cations for secondary ion mass spectrometry. II. Artefacts in material embedded in araldite or melamine.

Flotation on hot water (about 60 degrees C) which is frequently employed to stretch semithin sections on substrates for SIMS (secondary ion mass spectrometry) microscopy, is the cause of numerous artefacts. In the case of epoxy resin-embedded tissue, one observes loss of potassium and sodium and accumulation of calcium. The relative contrast of cell nuclei in the ionic images, is rapidly affected by these ion migrations. After prolonged contact with hot water, tissue becomes uniformly emissive. In the case of hydrosoluble resin-embedded tissue, potassium and sodium do not appear to be affected by the action of water, which suggests that they are covalently bound with chelating sites buried beneath the layer of water bound to the surface of the macromolecules. Calcium accumulates, probably on widely exposed anionic sites. Moreover, the domains observed in hydrosoluble resin-embedded tissue shrink differently according to the proportion of water removed by melamine; this can provide interesting information on the initial equilibrium between water, ion sand macromolecules. Our results seem to support the assumption that bound water should play an important role in the preservation of both macromolecular architecture and ion distributions.     

Low incidence of bronchus-associated lymphoid tissue (BALT) in chronically inflamed human lungs

The relevance of bronchus-associated lymphoid tissue (BALT) in man is still under discussion. Animal experiments indicate that the development of BALT is dependent on microbial stimulation. Therefore, the incidence of BALT was investigated retrospectively in specimens removed during surgical procedures on patients with chronic pulmonary inflammation. All these patients had severe chronic bronchitis and bronchiectasis, but BALT was found in only 8%. In patients with BALT and a malignant tumor, occlusion of a bronchus with poststenotic pneumonia was always present and BALT was observed exclusively in areas peripheral to the occlusion. In man other compartments of the lung must be responsible for the immune function of BALT found in animals. Partly presented at the Congress of the Eur. Respir. Soc, 21.- 26.9.1991 in Brussels. (Abstract: Eur Respir J. 4, Suppl. 14:217p)     

The organotypic culture of human skin keratinocytes and fibroblasts to achieve form and function

We describe an organotypic model of human skin comprised of a stratified layer of human epidermal keratinocytes and dermal fibroblasts within a contracted collagen lattice. Feasible and reproducible production of the skin construct has required the use of traditional as well as specialized culture techniques. The configuration of the construct has been engineered to maintain polarity and permit extended culture at the air-liquid interface. Morphological, biochemical and kinetic parameters were assessed and functional assays were performed to determine the degree of similarity to human skin. Light and ultrastructural morphology of the epidermis closely resembled human skin. The immunocytochemical localization of a number of differentiation markers and extracellular matrix proteins was also similar to human skin. Kinetic data showed a transition of the epidermal layer to a morein vivo-like growth rate during the development of the construct at the air-liquid interface. The barrier properties of the construct also increased with time reaching a permeability to water of less than 2%·h after approximately 2 weeks at the air-liquid interface which is still on average 30-fold more water-permeable than normal human skin. The construct is currently used forin vitro research and testing and is also being tested in clinical applications.