Soil Suppressiveness to Fusarium Wilt of Melon, Induced by Repeated Croppings of Resistant Varieties of Melons

A field soil, artificially infested with pathogenic isolates of Fusarium oxysporum f. sp. melonis was continuously used for screening resistant varieties of melon to Fusarium wilt. After 9–10 years of continuous cropping with resistant varieties, the soil had developed induced suppressiveness. Seven to 9 experimental replantings of the induced suppressive soil with the susceptible cultivar of melon, ‘Ein-Dor', nullified its suppressiveness. This was expressed by 90 % disease incidence. Only 2 replantings were required to obtain the same disease incidence in an adjacent field of a conducive soil. Nonpathogenic isolates of F. oxysporum, isolated from the rhizospheres of melon seedlings, induced various degrees of soil suppressiveness when added to soil at various ratios to the pathogenic isolate.     

Lactose malabsorption in Polynesian and white children in the south west Pacific studied by breath hydrogen technique.

Lactose malabsorption was studied by a breath hydrogen technique in 139 Samoan and 68 white schoolchildren. The Samoans were studied in four locations, two in Western Samoa and two in New Zealand, and the white children in both the Cook Islands and New Zealand. The prevalence of malabsorption varied with location: for Samoans it ranged from 41% to 60% in Western Samoa and 0% to 35% in New Zealand; white children had rates of 27% in the Cook Islands and 5% in New Zealand. Environmental factors rather than genetic factors are likely to play the main part in initiating if not perpetuating lactose malabsorption. In both races lactose malabsorption had no effect on the acceptance of, consumption of, and number of gastrointestinal symptoms caused by milk and milk biscuits. Children who had symptoms after consuming a particular dairy product were more likely to say they disliked it than those who reported no symptoms.     

Stimulation of the hypothalamic-pituitary-adrenal axis and inhibition of growth hormone release via increased central noradrenaline neuronal activity by urethane anaesthesia in the rat: blockade by clonidine

Computerized gas chromatography-mass spectrometry was used to measure precisely the hypothalamic levels of noradrenaline (NA), dopamine and serotonin together with those of their major neuronal metabolites 3,4-dihydroxyphenylethyleneglycol (DHPG), 3,4-dihydroxyphenylacetic acid and 5-hydroxyindoleacetic acid in normal male rats 45 min after stimulation of hypothalamic-pituitary-adrenal function by urethane (1.3 g/kg) administration. Urethane treatment resulted in a significant elevation of central noradrenergic neuronal activity (NNA) as assessed from marked rises in hypothalamic DHPG concentrations and the ratio (DHPG/NA). At the same time there was significant stimulation of ACTH and corticosterone release and inhibition of growth hormone release. These hormonal and central effects of urethane (but not anesthesia) were inhibited when the alpha 2-agonist clonidine (150 micrograms/kg) was co-administered. Urethane had no major effect on hypothalamic dopamine or serotonin status. We propose that the release of ACTH and the suppression of growth hormone release following urethane anaesthesia is a result of activation of central NNA and suggest that the hormonal responses are mediated via hypothalamic noradrenergic facilitation of corticotrophin releasing factor and somatostatin release to the anterior pituitary.     

Effects of net blotch on growth and yield of spring barley

The effect of net blotch on the growth and yield of cv. Beatrice spring barley was examined in a greenhouse experiment. Separate inoculations at growth stages 21 and 34 reduced green leaf area, root weight, leaf sheath and stem weight and tiller number. The early inoculated plants, which responded and recovered more rapidly than later treated ones, suffered a loss in grain yield and this was related to the amount of disease, the loss in green leaf area and the reduction in unit leaf rate.     

Metabolic activity of bacterial cells enumerated by direct viable count.

The direct viable count (DVC) method was modified by incorporating radiolabeled substrates in microautoradiographic analyses to assess bacterial survival in controlled laboratory microcosms. The DVC method, which permits enumeration of culturable and nonculturable cells, discriminates those cells that are responsive to added nutrients but in which division is inhibited by the addition of nalidixic acid. The resulting elongated cells represent all viable cells; this includes those that are culturable on routine media and those that are not. Escherichia coli and Salmonella enteritidis were employed in the microcosm studies, and radiolabeled substrates included [methyl-3H]thymidine or [U-14C]glutamic acid. Samples taken at selected intervals during the survival experiments were examined by epifluorescence microscopy to enumerate cells by the DVC and acridine orange direct count methods, as well as by culture methods. Good correlation was obtained for cell-associated metabolic activity, measured by microautoradiography and substrate responsiveness (by the DVC method) at various stages of survival. Of the cells responsive to nutrients by the DVC method, ca. 90% were metabolically active by the microautoradiographic method. No significant difference was observed between DVC enumerations with or without added radiolabeled substrate.     

A highly sensitive chromogenic microtiter plate assay for plasminogen activators which quantitatively discriminates between the urokinase and tissue-type activators

A simple and highly sensitive chromogenic microtiter plate assay for plasminogen activators is described. The assay is based on plasmin cleavage of the synthetic tripeptide plasmin substrate H-D-norleucyl-hexahydrotyrosyl-lysine p-nitroaniline, which yields the yellow chromophore p-nitroanilide. Production of the latter compound is then quantitated spectrophotometrically at 405 nm on an ELISA plate reader. Linearity of the assay can be achieved over at least four orders of magnitude in a single experiment (0.01-100 milliPloug units) with appropriate incubation times. Capitalizing on tissue-type plasminogen activator's dependence on fibrin for enzymatic activity, the selective use of soluble fibrin products allows discrimination between urokinase and tissue-type activator. The utility of this aspect of the assay for the analysis of complex samples containing both types of plasminogen activators is demonstrated.     

The "manganese(III)-containing" purple acid phosphatase from sweet potatoes is an iron enzyme

An improved purification of the purple acid phosphatase from sweet potatoes has been developed, and the properties of the enzyme have been reexamined. Contrary to previous reports, (e.g., Y. Sugiura, et al., J. Biol. Chem., 256, 10664-10670 (1981) ), the enzyme contains two moles of iron and insignificant amounts of manganese. The specific activity of the iron-containing preparations is ca. 14 times higher than that reported previously for the purported "Mn(III)" enzyme. The sweet potato purple acid phosphatase does indeed bind manganese, but it can be removed by dialysis with no changes in specific activity or spectral properties.     

Slow- and fast-binding inhibitors of thermolysin display different modes of binding: crystallographic analysis of extended phosphonamidate transition-state analogues

The modes of binding to thermolysin of two phosphonamidate peptide inhibitors, carbobenzoxy-GlyP-L-Leu-L-Leu (ZGPLL) and carbobenzoxy-L-PheP-L-Leu-L-Ala (ZFPLA), have been determined by X-ray crystallography and refined at high resolution to crystallographic R-values of 17.7% and 17.0%, respectively. (GlyP is used to indicate that the trigonal carbon of the peptide linkage is replaced by the tetrahedral phosphorus of a phosphonamidate group.). These inhibitors were designed to be structural analogues of the presumed catalytic transition state and are potent inhibitors of thermolysin (ZGPLL, Ki = 9.1 nM; ZFPLA, Ki = 0.068 nM) [Bartlett, P. A., & Marlowe, C. K. (1987) Biochemistry (following paper in this issue)]. ZFPLA binds to thermolysin in the manner expected for the transition state and, for the first time, provides direct support for the presumed mode of binding of extended substrates in the S2 subsite. The mode of binding of ZFPLA displays all the interactions that are presumed to stabilize the transition state and supports the postulated mechanism of catalysis [Hangauer, D. G., Monzingo, A. F., & Matthews, B. W. (1984) Biochemistry 23, 5730-5741]. The two oxygens of the phosphonamidate moiety are liganded to the zinc to give overall pentacoordination of the metal. For the second inhibitor the situation is different. Although both ZFPLA and ZGPLL have similar modes of binding in the S1' and S2' subsites, the configurations of the carbobenzoxy-Phe and carbobenzoxy-Gly moieties are different. For ZFPLA the carbonyl group of the carbobenzoxy group is hydrogen bonded directly to the enzyme, whereas in ZGPLL the carbonyl group is rotated 117 degrees, and there is a water molecule interposed between the inhibitor and the enzyme. For ZGPLL only one of the phosphonamidate oxygens is liganded to the zinc. Correlated with the change in inhibitor-zinc ligation from monodentate in ZGPLL to bidentate in ZFPLA there is an increase in the phosphorus-nitrogen bond length of about 0.25 A, strongly suggesting that the phosphonamide nitrogen in ZFPLA is cationic, analogous to the doubly protonated nitrogen of the transition state. The observation that the nitrogen of ZFPLA appears to donate two hydrogen bonds to the protein also indicates that it is cationic. The different configurations adopted by the respective inhibitors are correlated with large differences in their kinetics of binding [Bartlett, P. A., & Marlowe, C. K. (1987) Biochemistry (following paper in this issue)]. These differences in kinetics are not associated with any significant conformational change on the part of the enzyme.(ABSTRACT TRUNCATED AT 250 WORDS)     

Secondary structure of 5S RNA: NMR experiments on RNA molecules partially labeled with nitrogen-15

A method has been found for reassembling fragment 1 of Escherichia coli 5S RNA from mixtures containing strand III (bases 69-87) and the complex consisting of strand II (bases 89-120) and strand IV (bases 1-11). The reassembled molecule is identical with unreconstituted fragment 1. With this technique, fragment 1 molecules have been constructed 15N-labeled either in strand III or in the strand II-strand IV complex. Spectroscopic data obtained with these partially labeled molecules show that the terminal helix of 5S RNA includes the GU and GC base pairs at positions 9 and 10 which the standard model for 5S secondary structure predicts [see Delihas, N., Anderson, J., & Singhal, R. P. (1984) Prog. Nucleic Acid Res. Mol. Biol. 31, 161-190] but that these base pairs are unstable both in the fragment and in native 5S RNA. The data also assign three resonances to the helix V region of the molecule (bases 70-77 and 99-106). None of these resonances has a "normal" chemical shift even though two of them correspond to AU or GU base pairs in the standard model. The implications of these findings for our understanding of the structure of 5S RNA and its complex with ribosomal protein L25 are discussed.     

Structural elements of bactopterin from Pseudomonas carboxydoflava carbon monoxide dehydrogenase

Bactopterin is a novel pterin occurring in bacterial molybdoenzymes as the organic portion of the molybdenum cofactor. Its structure is investigated here. The compound contains a single pterin ring and carries a side chain at carbon atom 6 of the pterin nucleus as indicated by the formation of pterin-6-carboxylic acid upon alkaline permanganate oxidation. Studies with phosphate-cleaving enzymes revealed the presence of two monophosphoric acid monoesters. The affinity of reduced bactopterin for thiol-Sepharose points to the presence of thiol(s) in active bactopterin.