Control of nitrification of fertilizer nitrogen: Effect of inhibitors,banding and nesting

Laboratory incubation and field experiments were conducted to evaluate thiourea, ATC (4-amino-1, 2, 4 triazole hydrochloride) and N-Serve 24 E (2-chloro-6-trichloromethyl-pyridine) as inhibitors of nitrification of fertilizer N. In the incubation experiment, most of the added aqueous NH₃ or urea was nitrified at 14 days on both soils, but addition of the inhibitors to fertilizer N decreased the conversion of NH₄−N to NO₃−N markedly. There was less nitrification for ATC and thiourea but not for N-Serve 24 E when the fertilizers and the inhibitors were placed at a point as opposed to when mixed into soil. After 28 days, ATC and N-Serve 24 E were more effective in inhibiting nitrification than thiourea. ATC and N-Serve 24 E also inhibited release of mineral N (NH₄−N+NO₃−N) from native soil N. In the uncropped field experiment, which received N fertilizers in the fall, nitrification of fall-applied N placed in the 15-cm bands was almost complete by early May in the Malmo soil, but not in the Breton soil. When ATC or thiourea had been applied with urea, nitrification of fall-applied N was depressed by May and the recovery of applied N as NH₄−N was greater with increasing band spacing to 60 cm or placing N fertilizer in nests (a method of application where urea prills were placed at a point in the soil in the center of 60×60 cm area). In late June, the percentage recovery of fall-applied N in soil as NH₄−N or mineral N increased with wide band spacing, or nest placement, or by adding ATC to fertilizer N on both soils. These results indicate that placing ammonium-based N fertilizers in widely-spaced bands or in nests with low rates of inhibitors slows nitrification enough to prevent much of the losses from fall-applied N. Scientific Paper No. 552, Lacombe Research Station, Research Branch, Agric, Can.     

Unsuccessful induction of low-zone tolerance to bovine serum albumin injected into the subarachnoid space

Introduction of T-dependent antigens into the subarachnoid space (isas) resulted in higher systemic antibody responses in mice than injections into the peritoneal cavity (ip) or other sites commonly used for immunization. Antibody production in isas immunized mice was not increased by treatment with cyclophosphamide (Cy) at doses known to abolish T-suppressor-cell activity, but such treatment increased antibody production in ip immunized mice toward the higher level which was observed in the isas immunized animals. Suppressor cell-dependent low zone tolerance (LZT) to TNP-BSA could not be induced by isas injections of deaggregated BSA (d-BSA). Conversely, mice which were unresponsive to ip injected d-BSA showed consistent systemic antibody responses when the antigen was injected isas. These observations indicate that immune responses initiated within the CNS are associated with relatively ineffective induction of systemic suppressor cell activity.     

Studies on the C-24 configurations of Δ7-sterols in theseeds of Cucurbita maxima

Uncertainties surrounding the structures of the Δ⁷-sterols in the seeds of Cucurbita maxima have been resolved. Seven components were found by TLC, GLC, HPLC, mass spectrometry and ¹H NMR. They were 24β-ethyl-5α-cholesta-7,22,25(27)-trien-3β-ol, 24β-ethyl-5α-cholesta-7,25(27)-dien-3gb-ol, avenasterol, spinasterol, 24-dihydrospinasterol, 24ζ-methyllathosterol and 25(27)-dehydrofungisterol. The ¹H NMR spectra indicated that the sterols with an ethyl substituent at C-24 occurred in the absence of their C-24 epimers. This seems to be the first instance of the detection of 25(27)-dehydrofungisterol in a higher plant.     

In vivo interactions of acrylonitrile with macromolecules in rats

The irreversible binding of [2,3-14C]acrylonitrile (VCN) to proteins, RNA and DNA of various tissues of male Sprague-Dawley rats after a single oral dose of 46.5 mg/kg (0.5 LD50) has been studied. Proteins were isolated by chloroform-isoamyl alcohol-phenol extraction. RNA and DNA were separated by hydroxyapatite chromatography. Binding of VCN to proteins was extensive and was time dependent. Radioactivity in nucleic acids was registered in the liver and the target organs, stomach and brain. DNA alkylation, which increased by time, was significantly higher in the target organs, brain and stomach (119 and 81 pmol/mg, respectively, at 24 h) than that in the liver. The covalent binding indices for the liver, stomach and brain at 24 h after dosing were, 5.9, 51.9 and 65.3, respectively. These results suggest that VCN is able to act as a multipotent carcinogen by alkylation of DNA in the extrahepatic target tissues, stomach and brain.     

Immunologic and clinical improvement of progressive coccidioidomycosis following administration of transfer factor

Three patients with progressive coccidioidomycosis were given preparations of transfer factor (TF). Adverse reactions to TF were minimal. Following TF administration two of these patients had prolonged clinical remissions in their coccidioidal disease. Cellular immune responses were sequentially evaluated by coccidioidininduced delayed-type skin tests, lymphocyte blast transformation and macrophage inhibition factor production (MIF). These three patients each exhibited different cellular immune patterns before and after TF administration. Two patients converted their coccidioidin skin tests, and one converted lymphocyte transformation response to coccidioidin. Also, TF apparently favorably affected the MIF response in all three patients.     

Differentiation of various types of biological oxidation of nitrogen in organic compounds

The various types of nitrogen which occur in organic compounds and which are susceptible to biological oxidation are clearly divided into groups depending upon the pK_a, of the constituent nitrogen. The enzymatic processes which give rise to the N-oxidation products are reviewed by a consideration of species differences, age of animal, pH optima, influence of inducing agents, inhibitors and microsomal pretreatments, as well as the stereochemistry of the nitrogen atom.From the data collected, a concept is developed which suggests that all basic amines (group I) are oxidised by a flavine adenine nucleotide (FAD)-dependent enzyme system, whereas non-basic nitrogen-containing compounds (group III) are oxidised by a cytochrome P450-dependent system.It is further suggested that compounds of intermediary pK_a,i.e. between 1 and 7 (group II), may be substrates for both enzyme systems, which would yield the same products, but by different processes. The extent to which N-oxidation occurs in a species would therefore depend on the pK_a of the substrate and the amounts and ratio of the two enzymes present, a lower pK_a favouring oxidation by the cytochrome P450 system and a higher pK_a favouring oxidation by the FAD system.In a similar manner, it is suggested that the oxidation of aromatic heterocyclic amines depends upon the pK_a of the nitrogen, compounds having a low pK_a being preferentially metabolised by nitrogen oxidation.     

小鼠卵母细胞减数分裂染色体的制备

PreparationofMeioticKarytypeofMouseOocyteLiChaojunYanLeipingZhangXiranChenYifeng(BiologyDepartmentofNanjingNormalUniversity,Nanjing210097)哺乳动物的卵母细胞的减数分裂过程中存在两次自发的停滞现象,第一次是在第一次减数分裂前期的双线期,这一静止期持续很长时间,一直到动物性成熟后卵母细胞进入发有周刎,在保住腺激素的作用下,卵母细胞的第一次减数分裂才重新启动．完成第一次减数分裂后．又停滞在第二次减数分裂的中期,在椅子或化学因素刺激的作用下,完成第二次减数分裂[4]．因此,对哺乳动物的卵母细胞在一…     

Succinate-ethanol fermentation in Clostridium kluyveri: purification and characterisation of 4-hydroxybutyryl-CoA dehydratase/vinylacetyl-CoA Δ3-Δ2-isomerase

Anaerobically prepared cell extracts of Clostridium kluyveri grown on succinate plus ethanol contained high amounts of 4-hydroxybutyryl-CoA dehydratase, which catalyzes the reversible dehydration of 4-hydroxybutyryl-CoA to crotonyl-CoA. The enzyme was purified 12-fold under strictly anaerobic conditions to over 95% homogeneity and had a specific activity of 123 nkat mg^-1. The finding of this dehydratase means that all of the enzymes necessary for fermentation of succinate plus ethanol by C. kluyveri have now been demonstrated to exist in this organism and confirms the proposed pathway involving a reduction of succinate via 4-hydroxybutyrate to butyrate. Interestingly, the enzyme is almost identical to the previously isolated 4-hydroxybutyryl-CoA dehydratase from Clostridium aminobutyricum. The dehydratase was revealed as being a homotetramer (m=59 kDa/subunit), containing 2±0.2 mol FAD, 13.6±0.8 mol Fe and 10.8±1.2 mol inorganic sulfur. The enzyme was irreversibly inactivated after exposure to air. Reduction by sodium dithionite also yielded an inactive enzyme which could be reactivated, however, up to 84% by oxidation with potassium hexacyanoferrate(III). The enzyme possesses an intrinsic vinylacetyl-CoA isomerase activity which was also found in 4-hydroxybutyryl-CoA dehydratase from C. aminobutyricum. Moreover, the N-terminal sequences of the dehydratases from both organisms were found to be 63% identical.     

Extracellular targeting of the vacuolar tobacco proteins AP24, chitinase and β-1,3-glucanase in transgenic plants

The Nicotiana tabacum ap24 gene encoding a protein with antifungal activity toward Phytophthora infestans has been characterized. Analysis of cDNA clones revealed that at least three ap24-like genes are induced in tobacco upon infection with tobacco mosaic virus. Amino acid sequencing of the purified protein showed that AP24 is synthesized as a preproprotein from which an amino-terminal signal peptide and a carboxyl-terminal propeptide (CTPP) are cleaved off during post-translational processing. The functional role of the CTPP was investigated by expressing chimeric genes encoding either wild-type AP24 or a mutant protein lacking the CTPP. Plants expressing the wild-type construct resulted in proteins properly sorted to the vacuole. In contrast, the proteins produced in plants expressing the mutant construct were secreted extracellularly, indicating that the CTPP is necessary for targeting of AP24 to the vacuoles. Similar results were obtained for vacuolar chitinases and -1,3-glucanases of tobacco. The extracellularly targeted mutant proteins were shown to have retained their biological activity. Together, these results suggest that within all vacuolar pathogenesis-related proteins the targeting information resides in a short carboxyl-terminal propeptide which is removed during or after transport to the plant vacuole.