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911.
Van der Lee T De Witte I A Drenth C Alfonso F Govers 《Fungal genetics and biology : FG & B》1997,21(3):278-291
Here we present the first comprehensive genetic linkage map of the heterothallic oomycetous plant pathogen Phytophthora infestans. The map is based on polymorphic DNA markers generated by the DNA fingerprinting technique AFLP (Vos et al., 1995, Nucleic Acids Res. 23: 4407-4414). AFLP fingerprints were made from single zoospore progeny and 73 F1 progeny from two field isolates of P. infestans. The parental isolates appeared to be homokaryotic and diploid, their AFLP patterns were mitotically stable, and segregation ratios in the F1 progeny were largely Mendelian. In addition to 183 AFLP markers, 7 RFLP markers and the mating type locus were mapped. The linkage map comprises 10 major and 7 minor linkage groups covering a total of 827 cM. The major linkage groups are composed of markers derived from both parents, whereas the minor linkage groups contain markers from either the A1 or the A2 mating type parent. Non-Mendelian segregation ratios were found for the mating type locus and for 13 AFLP markers, all of which are located on the same linkage group as the mating type locus. Copyright 1997 Academic Press 相似文献
912.
Alfonso Valiente-Banuet Alberto Rojas-Martínez María del Coro Arizmendi Patricia Dávila 《American journal of botany》1997,84(4):452-455
We document the pollination biology and mating systems of Neobuxbaumia mezcalaensis and Neobuxbaumia macrocephala, two Mexican giant columnar cacti. These two species form mixed forests in the western Tehuacan Valley, Mexico. The flowers of both N. mezcalaensis and N. macrocephala exhibit nocturnal anthesis, are self-incompatible, and are pollinated primarily by three species of nectar-feeding bats (Choeronycteris mexicana, Leptonycteris curasoae, and Leptonycteris nivalis). Neobuxbaumia mezcalaensis is androdioecious, a breeding system that appears to be uncommon among Cactaceae. Neobuxbaumia macrocephala is hermaphroditic. We hypothesize that columnar cacti show a geographical dichotomy in floral biology specialization that probably can be related to predictability in pollinator abundance. 相似文献
913.
Rolando Martínez J. Ismael S. Ayamante B. Juana A. Núñez-Alarcón Alfonso Romo de Vivar 《Phytochemistry》1979,18(9):1527-1528
The isolation and structure determination of two new sesquiterpene lactones of the heliangolide type, leptocarpin and 17,18-dihydroleptocarpin from Leptocarpha rivularis, are described. The structure of leptocarpin was established as the 8β-angeloyl ester of 3β,8β-dihydroxy germacra-4,11(13)-dien- 1(10)-oxido-6α,12-olide. The second component was the 17,18-dihydro derivative of leptocarpin. 相似文献
914.
Claudio Toniolo Giovanni Valle Gian Maria Bonora Marco Crisma Fernando Formaggio Alfonso Bavoso Ettore Benedetti Benedetto Di Blasio Vincenzo Pavone Carlo Pedone 《Biopolymers》1986,25(12):2237-2253
The x-ray diffraction analysis of the N-benzyloxycarbonyl homo-tripeptide from α-amino-isobutyric acid has shown the occurrence of an incipient 310-helix characterized by one type-III (or type-III′) β-bend followed by one oxy-analog of the same type of β-bend. This represents the first unequivocal observation of the latter conformation, where the O—H group of the COOH moiety present at the C-terminus of the peptide main chain plays the role of the hydrogen-bonding donor. These results have been compared with those of the same peptide in its monohydrate form and of its methyl ester derivative, the x-ray diffraction structures of which are also described here. 相似文献
915.
Alfonso Troisi Filippo Aureli Gabriele Schino Fabio Rinaldi Nicoletta de Angelis 《Ethology : formerly Zeitschrift fur Tierpsychologie》1990,86(4):303-310
Yawning behavior was studied in two species of macaques: the long-tailed macaque (Macaca fascicularis) and the Japanese macaque (M. fuscata). Japanese macaques yawned much more than long-tailed macaques. Age, sex, and dominance rank exerted different effects on yawning in the two species. In the long-tailed macaques, sex differences in frequency of yawning emerged only after sexual maturity; yawning rates increased significantly in both males and females as they reached sexual maturity; and, among males, dominance rank was positively correlated with frequency of yawning. Differently, in the Japanese macaques, males, both mature and immature, yawned more than same-aged females; sexual maturity was associated with an increase in yawning in males only; and male rank did not correlate with the frequency of yawning. Regardless of interspecific differences, the overall results supported only in part the finding that, in Old World monkeys, yawning is largely influenced by plasma concentrations of androgens. There was evidence that social factors were also important in influencing the age-sex class distribution of yawning. 相似文献
916.
The microdialysis technique was used to examine the effect of the neurotoxin domoate, an analog of glutamic acid, on striatal dopamine activity. Our results show that the intracerebral administration of different concentrations of domoate (100 and 500 M) produced increases in the extracellular levels of dopamine associated to decreases in the extracellular levels of its metabolites dihydroxyphenylacetate and homovanillate from rat striatum. These changes seem to be related according to a time sequence, indicating a possible effect on the metabolism of dopamine. Changes were also observed in locomotor activity (cycling behavior, sniffing around and chewing) in rats during the domoate infusion. The physiological mechanism by which domoate increased dopamine release remains to be worked out. 相似文献
917.
Teresa Garnatje Alfonso Susanna Ramon Messeguer 《Plant Systematics and Evolution》1998,211(1-2):57-70
The phylogenetic and phenetic analysis of 109 RAPD polymorphisms inS. nebrodensis, a perennial and self-incompatible endemic of four mountain ranges in Spain, andS. viscosus, a self-compatible annual widespread in Europe, as well asS. lividus, S. sylvaticus andS. vulgaris revealed a sister group relationship between the first two species. This result contrasts sharply with the earlier hypothesis based on isozyme variation thatS. viscosus originated from within a paraphyleticS. nebrodensis and that the two species represent a progenitor-derivative pair. After considering possible reasons for the sister group relationship found, including the possibility of rooting artefacts, it is concluded that neither the RAPD data nor the isozyme data allow to draw safe conclusions about the mode of speciation and therefore the relative age of the two species. As a consequence, the limited genetic variation ofS. viscosus in comparison toS. nebrodensis as revealed by both the RAPD and the isozyme data may reflect its population history, geographical distribution, reproductive ecology, or mode of dispersal just as well as its recent origin from a paraphyleticS. nebrodensis. The result of this study calls for a critical reexamination of other taxon pairs postulated to have a progenitor-derivative relationship on the basis of isozyme evidence. 相似文献
918.
Pierluigi Barbaro Claudio Bianchini Maurizio Peruzzini Alfonso Polo Fabrizio Zanobini
Piero Frediani
《Inorganica chimica acta》1994,220(1-2):5-19The complex [(PP3)OsH(N2)]BPh4 is a catalyst precursor for the regio- and stereoselective dimerization of HCCR (R=Ph, SiMe3) to (Z)-1,4-disubstituted-but-3-en-l-ynes (PP3=P(CH2CH2PPh2)3). In the presence of H2O or C2H5OH, the catalytic reaction with HCCSiMe3 selectively gives but-3-en-l-ynyl-trimethyisilane. A detailed study under different experimental conditions, the detection of some intermediates, and the use of isolated complexes in independent reactions, taken altogether, permit mechanistic conclusions which account for the observed products. A key-role is played by (vinylidene)σ-alkynyl complexes which transform into η3-butenynyl derivatives via intramolecular C---C bond formation. The Os(II) η3-butenynyl complexes are likely reagents in the rate determining step of the catalytic cycle, and produce free (Z)-1,4-disubstituted-but-3-en-l-ynes upon σ-bond metathesis reaction with HCCR. The 16-electron fragments [(PP3)OsX]+ (X = H, Cl, CCR) are capable of promoting the 1-alkyne to vinylidene tautomerism. In particular, the (vinylidene)hydride [(PP3)OsH{C=C(H)-SiMe3}]BPh4 has been isolated and properly characterized. Since the stoichiometric reaction of the latter compound with HCCSiMe3 gives vinyltrimethylsilane, the formation of (vinylidene)hydride species is suggested to be an effective step, alternative to 1-alkyne insertion, in the reduction of 1-alkynes to alkenes assisted by hydrido metal complexes. 相似文献
919.
920.
A “probabilistic” rather than a “deterministic” approach to the theory of neural nets is developed. Neural nets are characterized
by certain parameters which give the probability distributions of different kinds of synaptic connections throughout the net.
Given a “state” of the net (i.e., the distribution of firing neurons) at a given moment, an equation for the state at the
next moment of quantized time is deduced. Certain very special cases involving constant distributions are solved. A necessary
condition for a steady state is deduced in terms of an integral equation, in general non-linear. 相似文献