Localization of aluminium in the leaves of some aluminium-accumulating species

Summary Transverse sections of leaves of some aluminium-accumulating and nonaccumulating species of the cerrado vegetation of central Brazil were coloured using aluminon to identify the tissues where aluminium occurs or is deposited. None of the tissues of the nonaccumulating species showed evidence of high concentrations of Al. All of the aluminium accumulating species showed high concentrations of Al in all of the elements of the phloem of the midrib and the secondary veins and total absence of it in the vessel members, xylem fibres and the palisade parenchyma. Walls and contents of the collenchyma of the midrib, epidermal cells, guard cells of the stomata and spongy parenchyma showed evidence of high concentrations of Al in the accumulating species.     

The effect of H-21J disparity on induction of allotransplantation tolerance by Lentil Lectin

The effect of an H-21J disparity on skin graft survival was studied in 18 mouse donor-recipient strain combinations, in which the recipients were treated with an efficient immunosuppressant, lentil lectin (LCA). The simultaneous I-J disparity essentially had no (or a slightly adverse) effect on the graft survival times in strain combinations differing at the K and I-A loci or in the entire H-2 complex. In two strain combinations incompatible at the D locus, the simultaneous I-J disparity promoted graft survival. The disparity at the I-J locus therefore seems to have only a marginal effect on the survival of allografts in most of the LCA-treated recipients, but it may promote graft survival in some animals. A similar tolerance-promoting effect was also observed with D disparity.     

Ethanol and the γ-Aminobutyric Acid-Benzodiazepine Receptor Complex

Abstract: Ethanol appears to enhance γ-aminobutyric acid (GABA)-mediated synaptic transmission. Using radioligand binding techniques, we investigated the possibility that the GABA-benzodiazepine receptor complex is the site responsible for this effect. Ethanol at concentrations up to 100 m M failed to alter binding of [³H]flunitrazepam (FNZ), [³H]Ro 15-1788, or [³H]methyl-γ-carboline-3-carboxylate (MBCC) to benzodiazepine receptors, or of [³H]muscimol to GABA receptors in rat brain membranes. Scatchard analyses of the binding of these radioligands at 4°C and 37°C revealed no significant effects of 100 m M ethanol on receptor affinity or number. A variety of drugs as well as chloride ion increased binding of [³H]FNZ and/or [³H]muscimol, but these influences were not modified by ethanol. These findings indicate that ethanol probably potentiates GABAergic neurotransmission at a signal transduction site beyond the GABA-benzodiazepine receptor complex.     

Peculiarities of influenza infection caused by highly and poorly immunogenic strains of influenza virus

The authors studied the peculiarities of the course of experimental influenza infection induced by the administration of highly and poorly immunogenic strains of influenza virus to mice. Influenza viruses with varying immunogenic activity were obtained from the vaccine strain A/Victoria/35/72/50 (H3N2) by immunoselection modelling the process of natural selection. The administration of strains with high and poor immunogenicity to mice of the F1 (CBA X C57B1) line led to the development of acute influenza infection accompanied by reproduction of viruses in the tissue of the lungs and other internal organs. The poorly immunogenic strain 5/II-Victoria, unlike the initial virus A/Victoria/35 and its highly immunogenic variant 2/I-Victoria, is able to circulate for a long time in the organism of the infected animal causing development of chronic inflammatory processes and stimulating the formation of neoplasms. Immunogenicity is thus one of the factors determining the character of the course of experimental influenza infection. A conclusion was drawn concerning the epidemiological and aetiological importance of viruses with reduced immunogenicity and their role in the evolution of influenza virus. It is presumed that reduced immunogenicity is one of the adaptation mechanisms of aggression permitting the population of influenza virus to escape control by specific humoral immunity.     

Hybrids between tobacco crown gall cells and normal somatic cells of Atropa belladonna

Protoplast fusion of Nicotiana tabacum (B6S3) crown gall cells and Atropa belladonna leaf mesophyll cells was carried out. Hybrids were selected for their capacity to grow on hormone-free media and to green in light. Shoots incapable of rhizogenesis were regenerated on the same media and grafted onto normal plants of different species. 57 hybrid cell lines differing in their genetic constitution were produced. Analysis of hybrid lines involved the determination of the lysopine dehydrogenase (LpDH) activity and the molecular forms of esterase and amylase, a restriction analysis of chloroplast DNA and a cytogenetic study.Abbreviations LS-H Linsmaier and Skoog (1965) hormone-free medium - LpDH lysopine dehydrogenase     

Analysis of characters coded for by T-DNA using hybridization between tumorous and normal plant cells

In somatic hybrids between tumourous Nicotiana tabacum (B6S3) and normal mesophyll Atropa belladonna cells, the following traits, directly or indirectly connected with T-DNA gene expression and tumourous growth, were analysed: lysopine dehydrogenase activity (LpDH), shoot suppression, root suppression, ability to grow on media with D-lactose as a sole carbon source and resistance to 2-aminoethylcysteine, 5-bromodeoxyuridine and 5-methyltryptophan. Dominant (semidominant) expression was observed for all but one trait studied, e.g. shoot suppression which behaved as a recessive character.Abbreviations LS-H Linsmaier and Skoog (1965) hormone-free medium - NAA Naphtaleneacetic acid - BAP 6-Benzylaminopurine - 2,4-D 2,4-Dichlorophenoxyacetic acid - 5-BUdR 5-Bromodeoxyuridine - 2-AEC 2-Aminoethylcysteine - 5-MT 5-Methyltryptophan     

Sedimentation and resuspension in a New England salt marsh

Particulate matter in a salt marsh can undergo repeated sedimentation and resuspension. Sedimentation measured with sediment traps, increases with tidal amplitude in areas with fast tidal currents, but is unaffected by tidal amplitude in areas with slow currents. The total sedimentation of particulate nitrogen in areas with slow tidal currents is three times as large as the gross tidal exchanges of particulate nitrogen between the marsh and coastal waters. Net tidal export of particles by the marsh suggests that sedimentation is more than offset by resuspension. Resuspension of fine (4–40 µm) particles occurs early in the flood tide in tidal creeks with slow currents. This resuspension does not increase with tidal amplitude, suggesting that it is not caused by tidal currents.     

Memory model based on the plasticity of inhibiting neurons

A stochastic memory model based on the net of excitatory and inhibitory neurons is considered. Its learning ability is due to a decrease of the reactivity of inhibitory elements. Information capacity of such neuron net was estimated in relation to its structure parameters. It has been shown that in the definite range of their change the information capacity of the net under consideration significantly exceeds that of the neuron net with the memory based on the plasticity of excitatory elements.