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1.
The elongation rate, the gradient of the local elongation rate and the surface pH of maize roots were measured over 12 h. A data bank was constituted by storing these values. By sorting these results on the basis of different elongation rates, different classes of root were obtained. Two classes were chosen: the low-growth roots and the high-growth roots. The mean growth of these two root classes was stable with time and differed significantly from one another. The surface pH of the elongation zone was the same for the roots of these two classes, but the roots selected for their higher growth rate had a larger acid efflux in this zone. 相似文献
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F. Fontaine E. Kiefer C. Clément M. Burrus J. L. Druelle 《Trees - Structure and Function》1999,14(2):83-90
In the present work, we described the fate of proventitious epicormic buds on the trunks of 40-year-old Quercus petraea trees and in parallel the vascular trace they produced in the wood. Our results show that small and large individual epicormic
buds can survive as buds for 40 years and that both are composed of a terminal meristem and scales. Meristematic areas are
detected in the scale axils of small buds; in addition to these meristems the large buds also have secondary bud primordia.
The small buds are connected to the pith of the main stem by a unique trace, whereas the large buds are connected by one or
multiple traces. A single trace might imply that the whole bud is still alive and multiple traces might indicate that the
terminal meristem has died. In the latter case, each trace is connected to a secondary bud of the large bud. The buds found
in a cluster are composed of a terminal meristem and scales with axillary meristems in the scale axils. A cluster is connected
to the pith of a stem either by a unique trace when it seems to be the result of partial abscission of an epicormic shoot
or multiple traces when it might have originated from an epicormic bud in which the terminal meristem has died. Whatever the
type of the bud, the vascular trace in the bark is composed of a cambium, secondary xylem and parenchyma cells and the trace
present in the wood had parenchyma cells with vestiges of secondary xylem. Each year, the vascular trace should be produced
in the bark by the cambium of the tree but not by the bud itself. On 40-year-old Q. petraea, we observed a proliferation of epicormic buds and in parallel a multiplication of the number of vascular traces in the trunk,
but the knots caused by the traces of epicormic buds in the wood, either as individuals or in clusters, are minor since their
colours are only slightly darker than those of woody rays and they are less than 2 mm in diameter. The knots will appear when
epicormic buds develop into shoots.
Received: 30 March 1999 / Accepted: 09 June 1999 相似文献
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Peter O''Connell G. Mark Lathrop Mark Leppert Yusuke Nakamura Ulrich Müller Jean-Marc Lalouel Ray White 《Genomics》1988,3(4):367-372
We have constructed a primary genetic map of human chromosome 18 consisting of 11 DNA markers and one serological marker (JK). Two of these loci define highly polymorphic VNTR systems. The markers define a continuous genetic linkage map of 97 cM in males and 205 cM in females; female genetic distances in a panel of 59 three-generation families were consistently about twice those observed in males. The high odds in support of the linear order of the markers on this recombination map, and the extent of coverage of chromosome 18, indicate that this map will permit efficient linkage studies of human genetic diseases that may be segregating on chromosome 18 and will provide anchor points for development of high-resolution maps for this chromosome. 相似文献
6.
High-level expression of a tobacco chitinase gene in Nicotiana sylvestris. Susceptibility of transgenic plants to Cercospora nicotianae infection 总被引:12,自引:0,他引:12
Jean-Marc Neuhaus Patricia Ahl-Goy Ursula Hinz Susan Flores Frederick Meins Jr. 《Plant molecular biology》1991,16(1):141-151
Endochitinases (E.C. 3.2.14, chitinase) are believed to be important in the biochemical defense of plants against chitin-containing fungal pathogens. We introduced a gene for class I (basic) tobacco chitinase regulated by Cauliflower Mosaic Virus 35S-RNA expression signals into Nicotiana sylvestris. The gene was expressed to give mature, enzymatically active chitinase targeted to the intracellular compartment of leaves. Most transformants accumulated extremely high levels of chitinase-up to 120-fold that of non-transformed plants in comparable tissues. Unexpectedly, some transformants exhibited chitinase levels lower than in non-transformed plants suggesting that the transgene inhibited expression of the homologous host gene. Progeny tests indicate this effect is not permanent. High levels of chitinase in transformants did not substantially increase resistance to the chitin-containing fungus Cercospora nicotiana, which causes Frog Eye disease. Therefore class I chitinase does not appear to be the limiting factor in the defense reaction to this pathogen. 相似文献
7.
Jean-Marc Gilli Paolo Mariani Franco Rustichelli Bin Yang Hervé Delacroix 《Molecular Engineering》1992,2(2):177-188
We recently showed that a side-chain industrial co-oligosiloxane presents a quenchable enlarged blue phase behaviour at the cholesteric-isotropic phase transition. In this paper, we present the results of a structural study based on X-ray diffraction, differential scanning calorimetry and optical measurements. In particular, the smectic A organisation is demonstrated in the lower temperature domain, which was hitherto understood as a cholesteric phase. A structural model for this phase is proposed on the basis of the analysis of the anisotropic scattering of stretched fibers. Our results also suggest that the observed glass transition is indeed a rather complex phenomenon, which seems to involve not only the freezing of the main chains, but also smectic correlations at the side-chain level. Moreover, the calorimetric study indicates that, notwithstanding the conservation of the processed film's optical properties, low kinetic reorganisations occur at room temperature. 相似文献
8.
F Fontaine F Vasseur J B Savary M Menais M Roussel M M Deminatti 《Annales de génétique》1988,31(2):102-104
Prenatal diagnosis of cystic fibrosis was performed with linked DNA probes in a couple with a 1:4 risk. The limits and the future of molecular prenatal diagnosis are discussed. 相似文献
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