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1.
13C-nmr has been employed to probe the molecular conformation and crystal structure of (1 → 6)-β-D -glucan (pustulan) in the solution, gel, and solid states. CP/MAS 13C-nmr spectra recorded for partially crystalline solid pustulan display a resonance near 82 ppm that is absent in solution spectra. The intensity and peak width of this resonance were found to depend on relative crystallinity as determined by x-ray diffraction. CP/MAS spectra of aqueous pustulan gels also exhibit the 82-ppm resonance, suggesting that the gelation mechanism may involve microcrystalline junction zones. Since the 82-ppm resonance is absent in the CP/MAS spectrum of the (1 → 6)-β-linked dimer gentiobiose, we tentatively conclude the crystal structure of this dimer does not adequately model the yet undetermined structure of pustulan. 相似文献
2.
3.
Direct sequencing of the mitochondrial displacement loop (D-loop) of shrews
(genus Sorex) for the region between the tRNA(Pro) and the conserved
sequence block-F revealed variable numbers of 79-bp tandem repeats. These
repeats were found in all 19 individuals sequenced, representing three
subspecies and one closely related species of the masked shrew group (Sorex
cinereus cinereus, S. c. miscix, S. c. acadicus, and S. haydeni) and an
outgroup, the pygmy shrew (S. hoyi). Each specimen also possessed an
adjacent 76-bp imperfect copy of the tandem repeats. One individual was
heteroplasmic for length variants consisting of five and seven copies of
the 79-bp tandem repeat. The sequence of the repeats is conducive to the
formation of secondary structure. A termination-associated sequence is
present in each of the repeats and in a unique sequence region 5' to the
tandem array as well. Mean genetic distance between the masked shrew taxa
and the pygmy shrew was calculated separately for the unique sequence
region, one of the tandem repeats, the imperfect repeat, and these three
regions combined. The unique sequence region evolved more rapidly than the
tandem repeats or the imperfect repeat. The small genetic distance between
pairs of tandem repeats within an individual is consistent with a model of
concerted evolution. Repeats are apparently duplicated and lost at a high
rate, which tends to homogenize the tandem array. The rate of D- loop
sequence divergence between the masked and pygmy shrews is estimated to be
15%-20%/Myr, the highest rate observed in D-loops of mammals. Rapid
sequence evolution in shrews may be due either to their high metabolic rate
and short generation time or to the presence of variable numbers of tandem
repeats.
相似文献
4.
5.
Antibiotic production by strains of Gliocladium virens and its relation to the biocontrol of cotton seedling diseases 总被引:1,自引:0,他引:1
Strains of the fungal antagonist Gliocladium virens were separated into two distinct groups on the basis of secondary metabolite production in vitro. Strains of the ‘P’ group produced the antibiotics gliovirin and heptelidic acid but not the antibiotic gliotoxin and its companion, dimethylgliotoxin. Strains of the ‘Q’ group produced gliotoxin and dimethylgliotoxin but not gliovirin or heptelidic acid. Strains from both groups produced the antibiotic viridin and phytotoxin viridiol. Gliovirin was very inhibitory to Pythium ultimum but had no activity against Rhizoctonia solani, and strains that produce it were more effective seed treatment biocontrol agents of disease incited by P. ultimum. Conversely, gliotoxin was more active against R. solani than against P. ultimum, and strains that produced it were more effective seed treatments for controlling disease incited by R. solani. These results indicate that the antibiotic profiles of strains should be considered when screening strains for biocontrol efficacy, and that it may be necessary to treat seeds with a combination of strains in order to broaden the disease control spectrum. 相似文献
6.
Four terpenoid phytoalexins, desoxyhemigossypol (dHG), hemigossypol (HG), desoxyhemigossypol- 6-methyl ether (dMHG) and hemigossypol-6-methyl ether (MHG), were identified with HPLC analysis of extracts from the moderately Fusarium wilt resistant cotton var. TAMCOT CAMD-E ( Gossypium hirsutum ) inoculated with Fusarium oxysporum f. sp. vasinfectum (F. o. v.). Concentrations of dHG, HG, dMHG and MG in stem steles at 10 days after inoculation were 45.1, 175. 0, 38. 3 and 1. 6 (g g–1 fresh tissue, respectively. The bioassays demonstrated that all four phytoalexins were toxic to F. o. v. The ED50 's of dHG, dMHG and HG were calculated as 8. 8, 13. 4 and 29. 3 (g ml−1 , respectively. The very low solubility of MHG in the standard assay medium prevented the determination of its ED50 value. Only dHG is water soluble at levels that appear necessary to act as an effective phytoalexin. At 30 μg ml−1 , dHG kills all conidia and mycelia of F. o. v . Viable propagules of F. o. v. were recovered from the steles of inoculated plants 10 days after inoculation; however, the pathogen was restricted to a zone 15 cm above the hypocotyl inoculation site. Thus, the fungistatic action of dHG appears to contribute to the resistance of cotton to Fusarium wilt by preventing the systemic distribution of F. o. v . propagules. 相似文献
7.
大鼠胼胝体内神经肽Y免疫反应阳性纤维的发育 总被引:1,自引:0,他引:1
本实验用免疫组织化学ABC法研究了大鼠胼胝体内神经肽Y免疫反应阳性(NPY-IR)纤维的生后发育。结果发现,许多NPY-IR纤维在大鼠出生时便存在于胼胝体内。NPY-IR胼胝体纤维的密度在生后1周内继续逐渐增高,在第2周内达到最高峰。之后,NPY-IR胼胝体纤维的密度逐渐下降,至第3周末时接近成年时的水平,即仅有少量NPY-IR纤维存在于胼胝体内。这些结果提示在大鼠早期生后发育过程中许多NPY-IR胼胝体纤维是暂时性的,其作用可能与大脑皮质的机能发育有关。 相似文献
8.
The vacuum-ultraviolet circular dichroism (VUCD) of chondroitin and chontroitin-6-sulfate has been measured to 160 nm for films and to 170 nm for D2O solutions. The pD-dependent dichroic behavior of these glycosaminoglycans in D2O is similar above 200 nm and is in agreement with previous studies. Near 190 nm, the CD band sign is also dependent on pD. VUCD spectra were recorded for films and solutions of poly(L -arginine). In trifluoroethanol the polypeptide is α-helical, while in D2O it exists as a random coil. The well-characterized coil–helix transition of poly(L -arginine) during complexation with chondroitin-6-sulfate was observed by VUCD, including the previously inaccessible entire π → π* band. By construction of difference spectra it was also possible to monitor the VUCD of the polysaccharide component during complexation. 相似文献
9.
Robert D. Stipanovic Alois A. Bell Marshall E. Mace Charles R. Howell 《Phytochemistry》1975,14(4):1077-1081
The triterpenoid aldehydes, gossypol (1), 6-methoxygossypol (2) and 6,6′-dimethoxygossypol (3); and the sesquiterpenoid aldehydes, hemigossypol (4) and methoxyhemigossypol (5), were isolated from 1-week-old roots of Gossypium hirsutum and G. barbadense and identified. This is the first report of 2 and 3 in nature and of 4 and 5 from healthy roots. Compounds 2 and 3 also constituted 30% of the total terpenoid aldehydes in the seeds of 1 cultivar of G. barbadense, but occurred only in trace quantities in those of G. hirsutum. Spectral data (UV, IR, NMR, MS) and proof of structure for 2 and 3 are presented. 相似文献
10.
Sreenath R. Palle LeAnne M. Campbell Devendra Pandeya Lorraine Puckhaber Lauren K. Tollack Sylvain Marcel Sabarinath Sundaram Robert D. Stipanovic Thomas C. Wedegaertner Lori Hinze Keerti S. Rathore 《Plant biotechnology journal》2013,11(3):296-304
Cottonseed remains a low‐value by‐product of lint production mainly due to the presence of toxic gossypol that makes it unfit for monogastrics. Ultra‐low gossypol cottonseed (ULGCS) lines were developed using RNAi knockdown of δ‐cadinene synthase gene(s) in Gossypium hirsutum. The purpose of the current study was to assess the stability and specificity of the ULGCS trait and evaluate the agronomic performance of the transgenic lines. Trials conducted over a period of 3 years show that the ULGCS trait was stable under field conditions and the foliage/floral organs of transgenic lines contained wild‐type levels of gossypol and related terpenoids. Although it was a relatively small‐scale study, we did not observe any negative effects on either the yield or quality of the fibre and seed in the transgenic lines compared with the nontransgenic parental plants. Compositional analysis was performed on the seeds obtained from plants grown in the field during 2009. As expected, the major difference between the ULGCS and wild‐type cottonseeds was in terms of their gossypol levels. With the exception of oil content, the composition of ULGCS was similar to that of nontransgenic cottonseeds. Interestingly, the ULGCS had significantly higher (4%–8%) oil content compared with the seeds from the nontransgenic parent. Field trial results confirmed the stability and specificity of the ULGCS trait suggesting that this RNAi‐based product has the potential to be commercially viable. Thus, it may be possible to enhance and expand the nutritional utility of the annual cottonseed output to fulfil the ever‐increasing needs of humanity. 相似文献