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排序方式: 共有1415条查询结果,搜索用时 125 毫秒
1.
Kenji Tsuji Shinji KitamuraHirofumi Makino 《Biochemical and biophysical research communications》2014
The kidneys are exposed to hypoxic conditions during development. Hypoxia-inducible factor (HIF), an important mediator of the response to hypoxia, is believed to have an important role in development. However, the relationship between HIF and branching morphogenesis has not been elucidated clearly. 相似文献
2.
3.
The capacity of preformation and neoformation and the structure of winter buds are vegetative attributes that may vary between plant species and according to ontogenetic stages of the same species. The present study describes and evaluates these features for the four tree species of Proteaceae occurring in Patagonia. In particular, it analyzes the structure and development of the distal buds of the trunk and the preformed or neoformed nature of the organs involved. Two of the species, Embothrium coccineum and Lomatia hirsuta, have scaly buds, in which primordia of green leaves are covered by cataphylls. The shoots of both species may include neoformed organs, more frequently so in juvenile trees. Lomatia ferruginea and Gevuina avellana have naked buds with a low number of primordia; in juvenile and adult trees of both species trunk shoots are entirely preformed. The structure of buds and shoots suggests two different growth modalities of the axes, which would be related to ecological breadth (narrower in the species with naked buds than in those with scaly buds) and distribution area of these species. The considerable morphological differences between the two Lomatia species studied raise the question whether they ought to be included in the same genus. 相似文献
4.
A general in vitro cloning system was established for four Helleborus species: H. argutifolius, H. foetidus, H. niger and H. orientalis. The plant material was introduced in vitro from axillary buds. A Murashige and Skoog (MS)—based medium (Murashige and Skoog
1962) was used supplemented with 2% (w/v) sucrose, 2-isopentenyladenine (2-iP) and 6-benzylaminopurine (BA). Multiplication
rates depended on the genotype and varied from 1.3 for H. foetidus till 3.8 for H. niger. The first results showed that the rooting phase could be done ex vitro. Rooting was induced by a drench for one week in
a solution of indole-3-butyric acid (IBA -3 mg l−1) and 1-naphthaleneacetic acid (NAA-1 mg l−1) at 5°C. 相似文献
5.
We studied the hibernation behavior of the water frog Rana lessonae and its hybridogenetic associate R. esculenta in their natural habitat during three successive winters. Animals caught in pitfall traps at a fenced pond were individually
marked with PIT tags and some (n=36) were additionally equipped with radio transmitters. Of the animals caught, 85% left the fenced pond for hibernation.
More R. esculenta remained inside the fenced area compared to R. lessonae. R. lessonae emigrated earlier in autumn and came back later in spring than R. esculenta, but the distance to their hibernation sites did not differ. Both species left the fenced pond earlier in the year when ambient
temperatures were lower. All radio-tracked animals hibernated in woodland, 3–7 cm below the surface in soil, under moss, fallen
leaves or small branches. Soil temperatures at the actual hibernation sites were significantly higher than at randomly chosen
control sites. A surprising finding was that most frogs changed their hibernation sites during winter, and often more than
once. Movements were more frequent in the warmer first half of the winter than in the cooler second half, but some animals
were active even on days with mean temperatures below 1°C. These results show that both species do not spend the whole winter
torpid in one particular hibernation site but move around, especially at higher temperatures. Most of the animals lost weight
during the winter, and the weight loss was greater in females than in males and higher in warm than in cold winters. To what
extent weight loss and survival is influenced by the chosen hibernation sites and the amount of movement during winter, and
whether this contributes to the differences in species and sex ratios found in mixed populations, needs more investigation.
Received: 4 August 1999 / Accepted: 15 November 1999 相似文献
6.
V. Selvakumar P. R. Anbudurai T. Balakumar 《In vitro cellular & developmental biology. Plant》2001,37(2):280-284
Summary A protocol for rapid in vitro propagation using nodal explants obtained from 2-yr-old, field-grown medicinal plants of Plumbago zeylanica L. belonging to the family Plumbaginaceae is described. High frequency bud break and fast development of shoots were induced
on Murashige and Skoog's basal medium supplemented with 27.2 μM adenine sulfate +2.46 μM indole-3-butyric acid (IBA). Induction of rooting was achieved by transferring the shoots to the same basal medium containing
4.92 μM IBA. Using our protocol from one twig of P. zeylanica (eight responsive nodes per explant shoot) within a period of 5 mo., eight plantlets could be raised. After a hardening period
of 4 wk, there was a 90% transplantation success in the field compared to the 60–65% survival of plantlets recorded in the
experiments of previous workers. The plantlets derived through in vitro propagation mimic the growth and morphological characteristics of the donor plants. 相似文献
7.
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
8.
Leaching losses of nitrogen from a clay soil under grass and cereal crops in Finland 总被引:1,自引:0,他引:1
Antti Jaakkola 《Plant and Soil》1984,76(1-3):59-66
Summary A 16-plot experimental field was established in 1975 on a clay soil in Jokioinen, Finland. The water discharge through tile drains was measured and its ammonium and nitrate N contents determined for each plot separately. The surface runoff was also measured and analysed. The annual runoff and the N leached from the surface of moderately fertilized (100 kg/ha/y N) cereal plots varied during 1976–1982 from 21 to 301 mm and from 2 to 7 kg/ha, respectively. The discharge of water and leaching of N through subdrains varied from 65 to 225 mm and from 1 to 38 kg/ha, respectively. The highest leaching was probably caused by a previous fallow. The annual N uptake by the crop varied between 41 and 122 kg/ha.Of the fertilizer-N used for cereals, 20% of that applied in the autumn was lost, but only 1 to 4 per cent was lost when applied in the spring. There was much less N leaching from ley than from barley plots, although the former was given twice as much N. The rate of N fertilization had only a very slight effect on N leaching from both ley and barley plots.The results were compared with those obtained in lysimeters filled with clay, silt, sand and peat soils. No definite conclusions can be drawn because the lysimeter experimental data are only for the first year. 相似文献
9.
The effect of winter temperatures on the timing of breeding activity in the common toad Bufo bufo 总被引:1,自引:1,他引:0
C. J. Reading 《Oecologia》1998,117(4):469-475
A 19-year study of a common toad population in south Dorset, UK, was carried out between 1980 and 1998. The daily arrival
of sexually mature male and female toads at a breeding pond was recorded each year. The timing of the main arrival of toads
at the breeding pond was highly correlated with the mean daily temperatures over the 40 days immediately preceding the main
arrival. When the temperatures were higher than average, breeding occurred significantly earlier in the year than if they
were either average or lower than average. During the study, the toad breeding seasons were early (2–13 February) in 5 years
(1989, 1990, 1993, 1995, 1998), late (16–23 March) in 2 years (1986, 1996) and average (25 February–8 March) during the remaining
12 years. Evidence was found suggesting that common toads have a daylength threshold of about 9 h, below which the migration
to the breeding pond does not occur. Evidence was also found indicating that common toads in southern England have a threshold
temperature for activity of about 6°C and that the onset of breeding activity is highly correlated with the number of days
during the 40 days prior to the main arrival at the breeding pond that were at or above this temperature. Predicting the start
of the main breeding migration to a pond in any year may be possible by comparing the pattern of the 40-day running mean daily
temperatures from 21 December the preceding year with those from previous years when the start of breeding activity is known.
Although all five of the earliest recorded toad breeding years occurred during the last 10 years, and were associated with
the occurrence of particularly mild winters, a significant trend towards earlier breeding in recent years compared with previous
years was not found.
Received: 16 July 1998 / Accepted: 14 September 1998 相似文献
10.
Rise and demise of cold-climate Picea abies forest in Sweden 总被引:1,自引:0,他引:1
LEIF KULLMAN 《The New phytologist》1996,134(2):243-256