Cowpea aphid performance and behaviour on two resistant cowpea lines

In a series of laboratory and climate chamber tests we compared the growth and behaviour of Aphis craccivora on one susceptible (ICV-1) and two aphid-resistant (ICV-11 and ICV-12) cowpea lines. The aphids' growth rates were much lower on the resistant cowpea lines than on the susceptible one, indicating strong antibiosis. In addition, the aphids invariably settled in higher numbers on the susceptible line than on either of the resistant. Compared to ICV-1, damaged leaves of the resistant line ICV-12 were settled upon to a higher degree than undamaged leaves, and leaf discs from the same line were even less resistant.On resistant lines individual aphids waited a significantly longer time before making their first test probe. Total probing time as well as the time preceding a decision to stay or leave was also longer.These results are discussed in relation to the possible mechanisms involved, and we also consider the effects of previous leaf feeding on the expression of resistance in the field.

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Résumé Au cours d'expériences au laboratoire et en chambres climatisées nous avons comparé la croissance et le comportement de A. craccivora sur une lignée sensible (ICV-1) et deux lignées résistantes (ICV-11 et ICV-12) de V. unguiculata. Les vitesses de croissance des pucerons ont été beaucoup plus lentes sur les lignées résistantes que sur la lignée sensible, ce qui révèle une forte antibiose. De plus, les pucerons atterrissent invariablement en plus grand nombre sur la variété sensible. Par comparaison avec ICV-1, les atterrissages sur lignée résistante ICV-12 étaient plus nombreux sur les feuilles endommagées que sur les feuilles intactes; les disques de feuilles de cette même lignée étaient encore moins résistants.Les pucerons ont séjourné individuellement un temps plus long sur les lignées résistantes avant de faire leur premier sondage. Le temps consacré aux sondages ainsi que le temps précédant de choix entre départ ou maintien sur la feuille étaient plus longs avec les lignées résistantes.Ces résultats ont été discutés en fonction des mécanismes impliqués. Nous avons aussi examiné les effets de la consommation antérieure sur les manifestations de la résistance dans la nature.

     

Phosphorus in sediments — speciation and analysis

Characterization of sediment phosphorus is commonly based on sequential chemical extractions, in which phosphorus is supposed to be selectively removed from different compounds in the sediments. The first extraction schemes were designed to quantify discrete chemical or mineralogical compounds. As extraction schemes have been tested on different sediments, several systematic errors have been detected and the schemes have been modified and simplified accordingly. Other chemical extractions or treatments have attempted to determine phosphorus bound to particles with a certain strength or binding energy, the purpose being to determine the labile, loosely bound, exchangeable, mobile or algal-available fraction of sediment phosphorus. All extraction procedures yield operationally defined fractions and cannot be used for identification of discrete phosphorus compounds. The many methodological modifications make it necessary to be cautious when comparing results from the literature in this field.     

Phosphatases; origin,characteristics and function in lakes

Phosphatases catalyze the liberation of orthophosphate from organic phosphorus compounds. The total phosphatase activity in lake water results from a mixture of phosphatases localized on the cell surfaces of algae and bacteria and from dissolved enzymes supplied by autolysis or excretion from algae, bacteria and zooplankton. External lake water phosphatases usually have pH optima in the alkaline region. Acid phosphatases generally seem to be active in the internal cell metabolism. The synthesis of external alkaline phosphatases is often repressed at high phosphate concentrations and derepressed at low phosphate concentrations. Phosphatase activity has therefore been used as a phosphorus deficiency indicator in algae and in natural plankton populations. The possibilities for this interpretation of phosphatase activity in lake water are limited, however, and this is discussed. The in situ hydrolysis capacity, i.e. the rate by which orthophosphate is released from natural substrates, is unknown. However, we advocate that this process is important and that the rate of substrate supply, rather than phosphatase activity, limits the enzymatic phosphate regeneration.     

Analytical determination of orthophosphate in water

Methods for orthophosphate determination and the problems of interferences are reviewed.An important group of methods utilizes the phosphomolybdate complex. The complexation step, the reduction step and the extraction step are treated separately and alternative procedures compared.Another group of methods uses ion association complexes; they are primarily used in physiology and not commonly used in water analyses today.Enzymatic methods for orthophosphate analysis in natural waters have been developed lately and are ready for application in selected waterbodies.Flame spectroscopic, fluorometric, gas chromatographic, ion exclusion chromatographic, inductively coupled plasma and other methods are also shortly presented.Radiobiological bioassays for orthophosphate are also available.In conclusion it was emphasized that the most common and reliable technique still is the molybdenum blue method as modified by Murphy & Riley (1962).The need for more specific and sensitive methods is particularly strong in investigations of phosphorus turnover and phosphorus limitation in natural waters. For these purposes the enzymatic phosphatase methods has advantages due to their specificity for orthophosphate and they might offer an alternative to the molybdenum blue method.     

Acute volume expansion as a physiological stimulus for the release of atrial natriuretic peptides in the rat

The concentration of immunoreactive atrial natriuretic peptide(s) (ANP) was measured in normovolemic conscious rats and 15 min after 10% and 20% blood volume expansion. A 20% blood volume expansion caused a 2-fold increase in plasma ANP. While plasma ANP increased linearly, atrial levels of ANP remained unaltered. The increase in plasma ANP parallelled increases of central blood volume and central venous pressure. It is concluded that acute blood volume expansion is a major physiological stimulus for the release of atrial natriuretic peptides into the circulation.     

Studies of the cellulolytic system of Trichoderma reesei QM 9414. Reaction specificity and thermodynamics of interactions of small substrates and ligands with the 1,4-beta-glucan cellobiohydrolase II

The 1,4-beta-glucan cellobiohydrolase II (CBH II) from Trichoderma reesei QM 9414 catalyses the hydrolysis of the 4-methylumbelliferyl beta-D-glycosides derived from cellotriose, cellotetraose and cellopentaose [MeUmb(Glc)n; n = 3 - 5]. The reaction has been followed by quantitative high-performance liquid chromatography. Specific activity for cellobiose removal at apparent substrate saturation were determined as (0.8 +/- 0.2) min-1 for MeUmb(Glc)3 and (9 +/- 2) min-1 for MeUmb(Glc)4. The enzyme showed a deviant specificity with MeUmb(Glc)5 as substrate. Two chromophoric products were formed simultaneously [MeUmb(Glc)3 and MeUmb(Glc)2] with turn-over numbers (17 +/- 4) min-1 and (21 +/- 6) min-1, respectively. Methylumbelliferyl beta-glucoside (MeUmbGlc) and the corresponding cellobioside [MeUmb(Glc)2] were used in equilibrium binding experiments. Both ligands yielded one binding site per molecule of Mr = 54000 upon forced flow dialysis (diafiltration). The association constants found were in fair agreement with those determined from MeUmb fluorescence quenching titrations. Quenching was total at all temperatures investigated for MeUmb(Glc)2, whereas for MeUmbGlc it increased from 80% to 100% between 2 degrees C and 20 degrees C. The association constants fitted linear van't Hoff plots in both cases. MeUmb(Glc)2 and MeUmbGlc were also used as indicator ligands to determine the association constants and thermodynamic parameters of several non-chromophoric ligands of CBH II. The binding of glucose increased the affinity for MeUmb(Glc)2 whereas it displaced MeUmbGlc from its complex. A putative binding site of the CBH II containing four subsites can be proposed. The thermodynamic data for methyl beta-D-glucopyranoside and cellobiose as ligands also point at an extended binding site.     

Pitfalls in the Dextran-coated charcoal assay of estrogen receptors in breast cancer tissue

This study investigated the influence of the degree of concentration of breast tumor cytosols on the apparent estrogen receptor content as measured by the Dextran-charcoal assay. It was found that the dilution of cytosols to 1-2 mg protein/ml frequently but not always causes highly underestimated receptor concentrations. This could not be explained by the protein loss through adsorption to the charcoal. The effect was also studied in the presence of gelatin, sodium molybdate or with limited trypsinization of the incubation mixture. Addition of 1 mg/ml gelatin in the Dextran-charcoal suspension was very useful in most cases in preventing dilution induced losses in receptor sites. Both trypsinization and addition of sodium molybdate produced increases in receptor concentrations that were not as susceptible to inactivation through dilution of the cytosol. These data suggest that the observed high variability in the dilution induced receptor losses can be explained by receptor heterogeneity: some receptor form(s) are either readily absorbed to or "stripped" by the charcoal particles. As a conclusion we recommend that in order to optimize the estrogen receptor assay as regards both binding sites and affinities the cytosol concentrations should be maintained as high as possible and a protein expander be included in the Dextran-charcoal suspension. Though sodium molybdate frequently gives considerable increases in estrogen binding sites it occasionally has an opposite effect. For this reason we hesitate to recommend its use in routine assays of estrogen receptors.     

Organization of early region 1B of human adenovirus type 2: identification of four differentially spliced mRNAs.

The mRNAs from early region 1B of adenovirus type 2 have been studied by Northern blot, S1 nuclease, and cDNA analysis. Two novel mRNAs, designated 14S and 14.5S, have been observed in addition to the previously identified 9S, 13S, and 22S mRNAs. They are 1.26 and 1.31 kilobases long and differ from the 13S and 22S mRNAs in being composed of three exons instead of two. Their two terminal exons are the same as those present in the 13S mRNA, whereas the middle exon is unique to each of the two novel mRNA species. The structures of the 14S and 14.5S mRNAs allow the prediction of their coding capacities: both mRNA species, like the 22S and 13S mRNAs, contain an uninterrupted translational reading frame encoding a 21,000-molecular-weight (21K) polypeptide. The 14S mRNA can, in addition, encode a 16.5K polypeptide which shares N-terminal and C-terminal sequences with the 55K polypeptide, known to be encoded by the 22S mRNA. The 14.5S mRNA species encodes a hypothetical 9.2K polypeptide which has the same N terminus as the 55K polypeptide but a unique C terminus. The two mRNAs differ in their kinetics of appearance; the 14.5S mRNA is preferentially expressed late after infection in contrast to the 14S mRNA, which is present in approximately equal amounts early and late after infection. Taken together with previously published information the results suggest that early region 1B of adenovirus type 2 encodes five proteins in addition to virion polypeptide IX. These have predicted molecular weights of 55,000, 21,000, 16,500, 9,200, and 8,100.     

Nuclease S1-sensitive sites in multigene families: human U2 small nuclear RNA genes.

We show here that human U2 small nuclear RNA genes contain a 'strong nuclease S1 cleavage site' (SNS1 site), a sequence that is very sensitive to digestion by nuclease S1. This site is located 0.50-0.65 kb downstream of the U2 RNA coding region. It comprises a 0.15-kb region in which (dC-dT)n:(dA-dG)n co-polymeric stretches represent greater than 90% of the sequence. Nuclease S1 is able to excise unit length repeats of the human U2 RNA genes both from cloned fragments and total human genomic DNA. The precise locations of the cleavage sites are dependent on the superhelicity of the substrate DNA. In negatively supercoiled substrates, cleavages are distributed over the entire 0.15-kb region, but in linearized substrates, they occur within a more limited region, mainly at the boundary of the SNS1 site closest to the human U2 RNA coding region. Nuclease S1 cleavage of negatively supercoiled substrates occurs at pHs as high as 7.0; in contrast, cleavage of linearized substrates requires a pH less than 5.0, indicating that supercoiling contributes to the sensitivity of this site. Mung bean nuclease gives results similar to that observed with nuclease S1.     

Splicing of the adenovirus-2 E1A 13S mRNA requires a minimal intron length and specific intron signals.

The adenovirus E1A region encodes three overlapping mRNAs, designated 9S, 12S and 13S. They differ from each other with regard to the length of the intron which is removed by RNA splicing. We have constructed E1A genes with deletions and insertions in the intervening sequence that is common to all three E1A mRNAs, in a search for signals which influence splicing of the 13S mRNA. Mutant plasmids were transfected into HeLa cells and the transiently expressed E1A mRNAs characterized by the S1 protection assay. The results show that five upstream and 20 downstream nucleotides are sufficient to allow for a correct utilization of the 5'-splice junction for the E1A 13S mRNA. Moreover, we show that a minimal intron length of 78 nucleotides is required for efficient 13S mRNA splicing. The ability of mutants with large intron deletions to maturate a 13S mRNA could partially be restored by expanding the intron length with phage lambda sequences. However, in no case was the normal splicing efficiency obtained with these mutants. In contrast, one mutant in which sequences from the authentic 13S mRNA intron were used to expand the intron expressed almost normal levels of 13S mRNA, thus suggesting that signals which specifically promote 13S mRNA splicing exist.