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81.
M R Sikov D N Rommereim J L Beamer R L Buschbom W T Kaune R D Phillips 《Bioelectromagnetics》1987,8(3):229-242
Evaluations of reproductive and developmental toxicology, including teratology, were included as part of a broad screening study in Hanford Miniature swine (HMS) to detect effects of exposure to electric fields. One group (E) was exposed to a uniform, vertical, 60-Hz, 30-kV/m electric field for 20 h/day, 7 days/week; sham-exposed (SE) swine were housed in a separate, environmentally equivalent building. The first generation (F0) gilts were bred after 4 months of study; some were killed for teratologic assays at 100 days of gestation (dg), and the others produced an F1 generation of offspring. The pooled incidence of terata in these litters (teratologic assays and live births) was similar in the E and SE groups. The F0 females, which produced the F1 generation, were bred again after 18 months of exposure and were killed at 100 dg. Malformation incidence in E litters (75%) was significantly greater than in SE litters (29%). No consistent differences in litter size, fetal mass, or mass of fetal organs were detected. The F1 gilts were bred at 18 months of age; defective offspring were found in significantly more of the E litters (71%) than in SE litters (33%). These F1 females were bred again 10 months later and teratologic assays were performed on their second litters at 100 dg. The percentage of litters with malformed fetuses was essentially identical in the E and SE groups (70% and 73%, respectively). There appears to be an association between chronic exposure to a strong electric field and developmental effects in swine, although the change in incidence of malformations between generations and between the first and second breedings makes it impossible to conclude unequivocally that there is a cause-and-effect relation. 相似文献
82.
Tatsuro Koike 《Journal of neurochemistry》1987,49(6):1784-1789
The binding and internalization of 125I-nerve growth factor (NGF) by PC12 pheochromocytoma cells was studied as a function of extracellular potassium concentration. Both surface-bound and internalized fractions of 125I-NGF associated with the cells under depolarizing conditions (50 mM K+) increased to 144 +/- 28% (average +/- SEM, six different cell preparations) and to 176 +/- 12% (n = 6), respectively, of those observed at 6.0 mM K+. Scatchard-type analysis of the data indicates increased sites for the binding and internalization of iodinated NGF by the cells. Similar enhancement was observed for cells treated with NGF as well. This voltage-dependent phenomenon was reversible, and also observed in the presence of veratridine. Moreover, withdrawal of extracellular Ca2+ abolished high K+-induced modulation of 125I-NGF binding and internalization, indicating that this effect may be mediated by Ca2+. 相似文献
83.
84.
85.
EFFECT OF MEDIA ON GROWTH AND INTERACTIONS BETWEEN A RANGE OF SOIL-BORNE GLASSHOUSE PATHOGENS AND ANTAGONISTIC FUNGI 总被引:10,自引:1,他引:9
JOHN M. WHIPPS 《The New phytologist》1987,107(1):127-142
86.
M. Agami 《Oecologia》1987,71(4):486-490
Summary The hills of the Negev highlands, west of Sede Boqer, are typically covered by various half-shrub communities, including the deciduous species of Helianthemum vesicarium Boiss., an Irano-Turanian element that grows only on north facing slopes, and H. ventosum Boiss., a Saharo-Arabian element which grows on both slopes but mainly on those facing south. Upon irrigation, plants of H. vesicarium preserve their natural rhythm of activity during winter and remain deciduous throughout the summer. On the other hand, under a similar irrigation treatment, the growth and flowering season of H. ventosum is modified and is extended well into the summer. Thus, H. ventosum shows a high phenological plasticity, while H. vesicarium seems to be very conservative. The different response of the two species to an improved water regime may partly explain the differences in their natural habitats: H. vesicarium on the more humid north facing slopes and H. ventosum mostly on the more arid and extreme south facing ones. Plants of both species which grow near boulders attain larger sizes and denser stands than those on the slopes.Age analysis based on xylem ring counts of 859 plants of the two natural populations showed that the plants did not exceed 14 years and most of them reached the age of some 5 years only. In general more seedlings are established during rainy year-clusters than during dry ones. However, no direct correlation between seedling establishment and the annual rainfall of specific years could be found.The rapid turnover of plants in the stands of both species of Helianthemum resembles the behavior of desert annuals rather than that of most desert shrubs. 相似文献
87.
Differential thermal analysis indicated that the frost resistance of winter rape leaves ( Brassica napus L. var. oleifera L. cv. Gòrczanski), collected from plants grown in the cold (5/2°C), relies mainly on their ability to supercool to −9 to −11°C, i.e. consists in freezing avoidance. Initiation of ice formation in the cold-acclimated leaves resulted in the death of more than 50% of the cells as determined with a conductivity method. The development of freezing tolerance appeared to be an attribute of the second stage of plant hardening and was induced by the exposure of plants to a slightly subzero temperature (−5°C) for 18 h. Such a treatment brought about a sudden and persistent water potential decrease in the leaves, despite the fact that they had reabsorbed water from the medium prior to water potential measurements. Water potential changes were associated with a higher growth capability of the leaves as checked by determinations of disk area increments. It is suggested that the increased frost tolerance of the cold-grown winter rape leaves, subjected to subfreezing temperature, is related to the decreased water potential of the tissue caused by changes in turgor and/or in osmotic pressures of the cells. 相似文献
88.
The function of the epidermis in auxinmediated elongation growth of maize (Zea mays L.) coleoptile segments was investigated. The following results were obtained: i) In the intact organ, there is a strong tissue tension produced by the expanding force of the inner tissues which is balanced by the contracting force of the outer epidermal wall. The compression imposed by the stretched outer epidermal wall upon the inner tissues gives rise to a wall-pressure difference which can be transformed into a water-potential difference between inner tissues and external medium (water) by removal of the outer epidermal wall. ii) Peeled segments fail to respond to auxin with normal growth. The plastic extensibility of the inner-tissue cell walls (measured with a constant-load extensiometer using living segments) is not influenced by auxin (or abscisic acid) in peeled or nonpeeled segments. It is concluded that auxin induces (and abscisic acid inhibits) elongation of the intact segment by increasing (decreasing) the extensibility specifically in the outer epidermal wall. In addition, tissue tension (and therewith the pressure acting on the outer epidermal wall) is maintained at a constant level over several hours of auxin-mediated growth, indicating that the inner cells also contribute actively to organ elongation. However, this contribution does not involve an increase of cell-wall extensibility, but a continuous shifting of the potential extension threshold (i.e., the length to which the inner tissues would extend by water uptake after peeling) ahead of the actual segment length. Thus, steady growth involves the coordinated action of wall loosening in the epidermis and regeneration of tissue tension by the inner tissues. iii) Electron micrographs show the accumulation of striking osmiophilic material (particles of approx. 0.3 m diameter) specifically at the plasma membrane/cell-wall interface of the outer epidermal wall of auxin-treated segments. iv) Peeled segments fail to respond to auxin with proton excretion. This is in contrast to fusicoccin-induced proton excretion and growth which can also be readily demonstrated in the absence of the epidermis. However, peeled and nonpeeled segments show the same sensitivity to protons with regard to the induction of acid-mediated in-vivo elongation and cell-wall extensibility. The observed threshold at pH 4.5–5.0 is too low to be compatible with a second messenger function of protons also in the growth response of the inner tissues. Organ growth is described in terms of a physical model which takes into account tissue tension and extensibility of the outer epidermal wall as the decisive growth parameters. This model states that the wall pressure increment, produced by tissue tension in the outer epidermal wall, rather than the pressure acting on the inner-tissue walls, is the driving force of growth.Abbreviations and symbols
E
el, E
pl
elastic and plastic in-vitro cell-wall extensibility, respectively
-
E
tot
E
el+E
pl
- FC
fusicoccin
- IAA
indole-3-acetic acid
- IT
inner tissue
- ITW
inner-tissue walls
- OEW
outer epidermal wall
-
osmotic pressure
-
P
wall pressure
-
water potential 相似文献
89.
Summary The root systems ofEucalyptus grandis W. Hill ex Maiden, irrigated with recycled municipal effluent at two sites in north-western Victoria, Australia, were studied
by excavation and coring. Trees at Robinvale were four years-old and were irrigated using micro-sprays that covered only 70%
of the ground surface area, whereas at Mildura, effuent was uniformly was uniformly applied to six years-old trees by flood
and sprinkler irrigation.
At Mildura where roots were excavated from a 2.80×2.80×1.20 m block of soil, a total root length of 1193 m.m−2 and a total root weight of 3.1 kg m−2 were estimated in the top metre. For roots >1 mm diameter, 77% of intercepts were at 0–30 cm, whereas only 50% were in the
50–100 cm soil horizon.
At both sites where roots in the top 30 cm were studied by coring, the vertical distributions of root intercepts, length and
weight were similar. Root length was greatest in the 0–10 cm soil horizon at both sites, and intercepts of roots <1 mm diameter
comprised 73% and 81% of all roots at Mildura and Robinvale respectively. Roots <1 mm diameter contributed 85% of total length
at both sites, but only 19% and 21% of total weight at Mildura and Robinvale respectively. The horizontal distribution of
roots differed at the two sites. With uniform application of effuent at Mildura, root intercepts and length were concentrated
in the centre of the irrigation bay, but at Robinvale, the concentration occurred closer to the tree row due mainly to the
different method of irrigation. Root weight at both sites was highest within 50 cm of the tree row.
Root densities of 0.11 to 0.57 cm cm−3 were estimated in the two plantations; these were similar to root densities measured inPinus radiata D. Don plantations up to 46 months old, but were considerably lower than those estimated for pastures. The implications of
the results for the management of irrigated plantations of eucalypts are discussed. 相似文献
90.
An isolate (G15) of a bacterium, frequently isolated from roots of various plant species, was identified asSerratia plymuthica. At low temperature (viz. 2–8°C), the studied isolated readily produced a red pigment which proved useful in recognizing the bacteria on reisolation.
In laboratory tests it exhibited strong antagonism againstBotrytis cinerea andGerlachia nivalis and moderate antagonism againstRhizoctonia solani, Fusarium culmorum andPythium sp. The bacterium significantly increased growth of lettuce plants when applied to the roots under non-sterile conditions
in greenhouse tests. Various strains ofSerratia plymuthica are supposed to be common as rhizosphere bacteria under Swedish conditions. 相似文献