Indigenous Arbuscular Mycorrhizal Fungi Associated with Acacia albida Del. in Different Areas of Senegal

The influences of seasons, plant age, and physicochemical properties of the soil on surface and deep biological arbuscular mycorrhizal fungus parameters associated with Acacia albida were assessed in different areas of Senegal. More indigenous arbuscular mycorrhizal propagules were found in the localities of the Sudano-Guinean zone (Djinaki and Kabrousse) than in those of the Sahelian zone (Louga and Diokoul), and species belonging to the genera Glomus, Gigaspora, Acaulospora, and Sclerocystis prevailed. The numbers of total and viable spores increased more during the rainy season than during the dry season (about 108% more total spores and 262% more viable spores). Similarly, both total and viable spores were more prevalent around young Acacia trees than old trees. However, the intensities of root colonization did not differ in each ecoclimatic zone.     

SR141716A, a potent and selective antagonist of the brain cannabinoid receptor

SR141716A is the first selective and orally active antagonist of the brain cannabinoid receptor. This compound displays nanomolar affinity for the central cannabinoid receptor but is not active on the peripheral cannabinoid receptor. In vitro, SR141716A antagonises the inhibitory effects of cannabinoid receptor agonists on both mouse vas deferens contractions and adenylyl cyclase activity in rat brain membranes. After intraperitoneal or oral administration SR141716A antagonises classical pharmacological and behavioural effects of cannabinoid receptor agonists. This compound should prove to be a powerful tool for investigating the in vivo functions of the anandamide/cannabinoid system.     

The Saccharomyces cerevisiae SGE1 gene product: a novel drug-resistance protein within the major facilitator superfamily

Several pleiotropic drug sensitivities have been described in yeast. Some involve the loss of putative drug efflux pumps analogous to mammalian P-glycoproteins, others are caused by defects in sterol synthesis resulting in higher plasma membrane permeability. We have constructed a Saccharomyces cerevisiae strain that exhibits a strong crystal violet-sensitive phenotype. By selecting cells of the supersensitive strain for normal sensitivity after transformation with a wild-type yeast genomic library, a complementing 10-kb DNA fragment was isolated, a 3.4-kb subfragment of which was sufficient for complementation. DNA sequence analysis revealed that the complementing fragment comprised the recently sequenced SGE1 gene, a partial multicopy suppressor of gal11 mutations. The supersensitive strain was found to be a sge1 null mutant. Overexpression of SGE1 on a high-copy-number plasmid increased the resistance of the supersensitive strain. Disruption of SGE1 in a wild-type strain increased the sensitivity of the strain. These features of the SGE1 phenotype, as well as sequence homologies of SGE1 at the amino acid level, confirm that the Sge1 protein is a member of the drug-resistance protein family within the major facilitator superfamily (MFS).     

Effects of gamma irradiation on the plasma membrane of suspension-cultured apple cells. Rapid irreversible inhibition of H+-ATPase activity

The effects of ionizing radiation, used in post-harvest treatment of fruit and vegetables. were investigated on cultured apple cells ( Pyrus malus L. cv. Royal Red) on a short-term period. Irradiation (2 kGy) induced an increase of passive ion effluxes from cells and a decrease of cell capacity to regulate external pH. These alterations are likely due to effects on plasma membrane structure and function and were further investigated by studying the effects of irradiation on plasma membrane H⁺-ATPase activity. Plasma membrane-enriched vesicles were prepared and the H⁺-ATPase activity was characterized. Irradiation of the vesicles induced a dose dependent inhibition of H⁺-ATPase activity. The loss of enzyme activity was immediate, even at low doses (0.5 kGy), and was not reversed by the addition of 2m M dithiothreitol. This inhibition may be the result of an irreversible oxidation of enzyme sulfhydryl moieties and/or the result of changes induced within the lipid bilayer affecting the membrane-enzyme interactions. Further analysis of the H⁺-ATPase activity was carried out on vesicles obtained from irradiated cells confirming the previous results. In vivo recovery of activity was not observed within 5 h following the treatment, thus explaining the decrease of cell capacity to regulate external pH.
This rapid irreversible inhibition of the plasma membrane H⁺-ATPase must be considered as one of the most important primary biochemical events occurring in irradiated plant material.     

Effect of snow removal on leaf water potential,soil moisture,leaf and soil nutrient status and leaf peroxidase activity of sugar maple

Effect of removal of snow cover in winter was investigated in an 80-year-old sugar maple (Acer saccharum Marsh.) stand in southern Quebec. We hypothesized that winter soil frost would induce some of the decline symptoms observed in sugar maple stands in southern Quebec in the early 1980's. Snow was continuously removed from around trees for a one week (partial removal) or for a four-month period (complete removal) during the 1990–1991 winter. Foliage and soils were sampled periodically during the summer of 1991. The complete snow removal treated trees showed decreased leaf water potential and increased peroxidase activity over most of the growing season. Foliar Ca was reduced in both snow removal treatments early in the growing season while foliar N was reduced in the complete snow removal trees late in the growing season. Soil NO ₃ ^– and K⁺ were elevated in both snow removal treatments at various times throughout the growing season. Prolonged soil frost in a sugar maple stand can induce lower leaf water potential, higher leaf peroxidase activity and early leaf senescence during the following growing season. Soil frost may have reduced nutrient uptake without affecting significantly the leaf nutrient status.     

Evidence that residues −15 to −46 of the haemolysin secretion signal are involved in early steps in secretion, leading to recognition of the translocator

We previously identified three well-dispersed mutations, E⁹⁷⁸-K, F⁹⁸⁹-L and D¹⁰⁰⁹-R within the haemolysin A signal region, located at positions –46, –35 and –15, with respect to the C-terminus, respectively. Each mutation reduces the efficiency of secretion two- to threefold leaving 30–45% of the wild-type activity. We have constructed by in vitro manipulations double mutants of HlyA carrying all combinations of these mutations and a triple mutant carrying all three mutations. The effects on secretion were determined and the results, including residual levels of secretion with the triple mutant of only 0.6%, compared with the wild type, indicated that these residues may interact to form a single function in the wild-type signal. To test this further, we developed a secretion competition assay in order to classify signal mutations. We demonstrated that a CIZ-HlyA fusion protein, containing the C-terminal 81 kDa of HlyA fused to virtually the whole LacZ protein, strongly inhibits the secretion of the wild-type HlyA co-expressed In the same cell. The properties of the fusion indicate that it blocks the translocator. The three mutations singly and in combinations were recombined in vitro into the 3′-end of the hybrid gene. In every case, the presence of a mutation in the secretion signal of the hybrid protein alleviated the inhibition of secretion of the co-expressed HiyA. All the mutations are therefore essentially recessive and we propose that they all affect an early function, probably recognition of the translocator, rather than a subsequent step involved in translocation or final release of the toxin to the medium. This would indicate that residues involved in recognition for steps     

Simple sequences

Simple sequences (or microsatellites) are stretches of monotonous repetitions of short (1–5 bp) nucleotide motifs that are distributed across the whole genome in eukaryotes. They are probably generated by slippage during replication and their primary mutation rate seems to be controlled predominantly by the efficiency of the mismatch repair system. Although most mutations in simple sequence loci appear to be neutral, some mutations in particular stretches have been implicated as having a role in human genetic diseases.     

Freshwater fish zoogeography in west Africa: faunal similarities between river basins

Synopsis Similarities between the freshwater fish faunas of 52 west African rivers have been investigated and three main zoogeographic regions recognized. The Sudanian region includes all rivers from Senegal to the Omo, as well as coastal basins from Ivory Coast to the Cross and the Wouri. The Upper Guinean region comprises the coastal basins from Guinea to Liberia and the Lower Guinean one, the coastal rivers of Cameroon and Gaboon. The Sudanian region can be sub-divided into a Sudanian region sensu stricto, including the Sahelo-Sudanese rivers, and the Eburneo-Ghanean region corresponding to coastal basins from the Cess (or Nipoué, Ivory Coast) to the Pra (Ghana). These delimitations give an highly significant within region faunal homogeneity, even if the effect of geographical proximity between rivers is removed. 21 to 71% of the fish species in each region are endemics. The present patterns of distribution are the result of past climatic and geological events affecting west Africa and, given this framework, the role of alternating wet and dry periods during the early Quarternary is emphasized as well as the importance of mountains as dispersal barriers. Role of recent river connections and links via lagoon is emphasized in explaining river faunal similarities within biogeographical regions.     

Tyrosine attack by free radicals derived from catalytic decomposition of carbon tetrachloride

The interaction between free radicals derived from the catalytic decomposition of carbon tetrachloride and tyrosine (the N-acetyl tyrosine ethyl ester, ATEE) under anaerobic and aerobic conditions was studied. The structure of the reaction products formed was desciphered by the GLC/MS analysis of their trimethylsilyl derivatives. Under anaerobic conditions the formation of the following products was found: (1) an unsaturated derivative of the amino acid; (2) the trimethylsilyl derivative of N-acetyl chloro tyrosine ethyl ester; (3) a hydroxyl adduct of ATEE ; (4) an ATEE adduct having a chlorine and a CCl₃ group in the molecule (it is suggested that CCl₃ is attached to the benzyl carbon and the chlorine located in the benzene ring); (5) an ATEE adduct having only a CCl₃ group tentatively assigned to be located on the benzyl carbon; and (6) and (7) were found to be two isomers of an ATEE having one CCl₃ on the aromatic ring. Under aerobic conditions the following reaction products were identified: Two products which were similar to those numbered (1) and (2) and formed anaerobically; (8) and (11) two isomeric dichlorinated adducts of ATEE; (9) and (10) two isomeric dichlorinated monohydroxylated derivatives of ATEE. Concerning the potential relevance of these findings, we consider that if similar interactions to those here reported occurred during CCl₄ poisoning, the activity of enzymes having tyrosine in their active center might result in impairment. Further, enzymes operating on tyrosine moieties in proteins might be perturbed in their action if tyrosine groups were attacked by the free radicals arising from catalytic decomposition of CCl₄ evidenced here.