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21.
Abstract. The location and distribution of symbiotic bacteria during floral development in Ardisia crispa (Thunb.) A.DC., a species characterized by bacterial leaf nodules, has been studied using light, scanning and transmission electron microscopy. During early floral development, bacteria in mucilage derived from host plant trichomes, become enclosed in a small conical chamber on top of the placenta, as a result of the closure and fusion of the carpel initials. The placental epidermal cells, which appear to be secretory in nature, become detached apically in places forming a network of grooves which traverse the placental surface. The symbiotic bacteria are preferentially located in these grooves. As growth and development of the placenta proceed, the grooves widen and deepen to form channels. The cells lining these channels secrete a mucilaginous material. The network of channels covers the entire placental surface and terminates at the placental margins surrounding the ovules. Bacteria are found within the channels, at the ends of the channels near the margin of the placenta, on the surface of the ovules and in the micropyle. It is suggested that these mucilage-filled channels are responsible for, and a prerequisite of, ensuring that the bacterial partner is efficiently transmitted from one host generation to the next by providing a mechanism by which the bacteria arc accurately placed within the developing seed. 相似文献
22.
A. S. Paschoa M. E. Wrenn N. P. Singh F. W. Bruenger S. C. Miller M. Cholewa K. W. Jones 《Biological trace element research》1987,13(1):275-282
Several geological formations of the Utah-Colorado mining region mined for uranium ore during and after World War II had been
mined earlier for vanadium. Therefore, most miners and millers from that region were exposed to those metals’ ores or tailings
at one time or another. Preliminary investigation to determine uranium and vanadium retained in the lungs of a former uranium
miner and miller from this region, who died of lung cancer (mesothelioma), showed a high nonuniform distribution of vanadium.
This observation led to the hypothesis that the vanadium content in the lungs could be associated with inhaled particles.
Further examination of spectra of characteristic X-rays obtained by scanning particle-induced X-ray emission (microPIXE) of
an autopsy sample of this lung indicated that vanadium was indeed present in localized sites within the 20-μm spatial resolution
of the proton beam. This work points out that the microPIXE-RBS (Rutherford backscattering) test for vanadium can be used
for site localization of inhaled particles retained in the lungs. Further studies are in progress to: (i) locate uranium-bearing
particles in lung tissues of former uranium miners and millers; and (ii) evaluate the local doses of alpha radiation received
from these particles. 相似文献
23.
The symptoms of the leaf scald disease can be reproduced in vitro through the inoculation of sugarcane tissue culture plantlets. The pathogen is detected in the inoculated plantlet and is maintained at the surface of the base of the plantlets grown in vitro. Two strains of X. albilineans belonging to different serovars and lysovars reacted like pathotypes. The importance of the plant incubation temperature is clearly demonstrated. Further, in vitro the disease goes through the same phase of latency as in the field. 相似文献
24.
25.
Foliar litterfall nutrient concentrations were analysed for selected members of Taxodiaceae and Cupressaceae families andPseudotsuga menziesii for two arboreta in western Oregon and Washington. Nutrient results between arboreta show similar concentrations with the
exception of magnesium, which may be the result of historical land use. Nutrient concentrations between species vary considerably.Pseudotsuga menziesii is particularly distinctive from the Cupressaceae and Taxodiaceae by retaining large amounts of phosphorus and potassium.
Taxodiaceae is distinctive by high concentration of Mg while Cupressaceae retains calcium, especiallyChamaecyparis nootkatensis. Results suggest that all members of Taxodiaceae and Cupressaceae retain considerably more Ca than Pinaceae in foliar litter. 相似文献
26.
M. K. Banerjee M. K. Kalloo 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(5):707-710
Summary One hundred and twenty-two varieties, lines and wild accessions of Lycopersicon were screened under three different regimes during the autumn/winter season of 1982–83 and 1983–84 for resistance to tomato leaf curl virus (TLCV). L. hirsutum f. glabratum (B6013) and L. hirsutum f. typicum (A1904) proved to be highly resistant to TLCV in all three environments. Various accessions of L. peruvianum were also highly resistant. L. pimpinellifolium (A1921) exhibited no TLCV symptoms within 90 days. Of the cultivated varieties, Acc 99 exhibited the minimim score for susceptibility; AC 142, Collection No. 2, Kalyanpur Angurlata and HS 101 had a low rating for virus incidence. The inheritance of resistance was studied in the interspecific crosses between a TLCV resistant line of L. pimpinellifolium (A1921) and five (HS 101, HS 102, HS 110, Pusa Ruby and Punjab Chhuhara) susceptible cultivars of L. esculentum. Parents, F1, F2 and backcross progenies were artificially inoculated with local strains of TLCV using vector the viruliferious whitefly, Bemisia tabaci (Genn.). Data indicated that the resistance of L. pimpinellifolium (A 1921) is monogenic and incompletely dominant over susceptibility. 相似文献
27.
Particulate organic matter in a mountain stream in the south-western Cape,South Africa 总被引:2,自引:2,他引:0
The quality and quantity of allochthonous inputs and of benthic organic matter were investigated in a second-order, perennial mountain stream in the south-west Cape, South Africa, between April 1983 and January 1986. Although the endemic, riparian vegetation is sclerophyllous, low and evergreen, inputs of allochthonous detritus to the stream (434 to 500 g m–2y–1) were similar to those recorded for riparian communities worldwide, as were calorific values of these inputs (9548 to 10 032 KJ m–2y–1). Leaf fall of the riparian vegetation is seasonal, occurring in spring (November) as discharge decreases, resulting in retention of benthic organic matter (BOM) on the stream bed during summer and early autumn (maximum 224 g m–2). Early winter rains (May) scoured the stream almost clean of benthic detritus (winter minimum 8 g m–2). Therefore, BOM was predictably plentiful for about half of each year and predictably scarce for the other half. Coarse BOM (CBOM) and fine BOM (FBOM) constituted 46–64% of BOM standing stock, ultra-fine BOM (UBOM) 16–33% and leaf packs 13–24%. The mean annual calorific value of total BOM standing stock was 1709 KJ m–2. Both standing stocks and total calorific values of BOM were lower than those reported for streams in other biogeographical regions. Values of C:N ratios decreased with decrease in BOM particle size (CBOM 27–100; FBOM 25–27; UBOM 13–19) with no seasonal trends. The stream is erosive with a poor ability to retain organic detritus. Its character appears to be dictated by abiotic factors, the most important of which is winter spates. 相似文献
28.
Michael A. Keller 《Entomologia Experimentalis et Applicata》1987,43(1):55-59
Walking speeds of female Trichogramma exiguum Pinto & Platner were fastest on maize and soybean (12 cm/min), intermediate on tomato (8 cm/min), and slowest on woolly mullein, Verbascum thapsus (3 cm/min). Similarly, rates of turning along the paths of walking T. exiguum were smallest on maize (median angle=0°±15°), intermediate on soybean and tomato, and greatest on V. thapsus (median angle=30°±15°). Leaf trichome density and morphology influenced walking behavior. Walking was slowed and flight initiation delayed for T. exiguum walking on Amaranthus hybridus leaves compared to either maize or filter paper. When inundative releases are conducted, the effects of plant surfaces on searching rates and arrestment should be considered in determining release rates of Trichogramma spp.
Résumé La vitesse de marche a été déterminée en lâchant des individus sur chaque substrat végétal et en traçant leur parcours sur une plaque de verre placée à 9 mm au dessus du sujet. Les déviations angulaires de portions successives des tracés, longues de 1 mm, ont été utilisées pour mesurer les taux de changement de direction. Dans une deuxième expérience, des individus ont été lâchés au milieu d'une cercle de 40 mm de diamètre sur chaque substrat et les temps écoulés avant l'envol ou pour atteindre le bord du cercle à la marche ont servi à évaluer respectivement la propension au vol et la vitesse de déambulation.Les vitesses de marche ont été plus rapides sur maïs et soja (12 cm/min), moyennes sur tomate (8 cm/min) et les plus lentes sur Verbascum thapsus (Scrophulariaceae) (3 cm/min). De le même façon, les angles de changement de direction au cours des marches effectuées par T. exiguum ont été plus petits sur maïs, moyens sur soja et tomate, et plus grands sur V. thapsus. Chez T. exiguum marchant sur des feuilles d'Amaranthus hybridus L. (Amaranthaceae), la marche a été plus lente et l'envol plus tardif que sur maîs ou papier filtre.Lors de lâchers inondatifs, les effets des surfaces végétales sur les vitesses d'exploration et d'arrêt devraient être pris en compte pour déterminer les vitesses de lâcher des Trichogramma spp.相似文献
29.
Fructan biosynthesis in excised leaves of Lolium temulentum L. 总被引:2,自引:2,他引:0
ANDREW J. CAIRNS 《The New phytologist》1989,112(4):465-473
30.
Interaction between nitrogen and photon flux density in birch seedlings at steady-state nutrition 总被引:7,自引:0,他引:7
Birch ( Betula pendula Roth.) was investigated under steady-state nutrition and growth at different incident photon flux densities (PFD) and different relative addition rates of nitrogen. PFD had a strong influence on the relative growth rate at optimum nutrition and on the nitrogen productivity (growth rate per unit of nitrogen) but little effect on the formal relationships between nitrogen and growth, i.e. PFD and nitrogen nutrition are orthogonal growth factors. At a given suboptimum nitrogen (the same distance from optimum), increased PFD increased the relative growth rate and, therefore, the relative uptake rate and the required relative addition rate in accordance with the theoretical equality between these three parameters at steady-state nutrition. Correspondingly, at a given suboptimum relative addition rate, increased PFD decreased nitrogen status (larger distance from optimum) at an unchanged relative growth rate. Nutrient uptake rate, dry matter content, and partitioning of biomass and nutrients are strongly influenced by nitrogen status. PFD influences these characteristics, but only to an extent corresponding to its effect on the nitrogen status. The influence of PDF on the relative growth rate at optimum and on nitrogen productivity is well described by hyperbolic relationships, similar to reported PFD/photosynthesis relationships. These expressions for plant growth as well as the productivities of leaf area and quantum appear to be valuable characteristics of plant responses to light and nutrition. Although the calculated PFD/growth relationships indicate saturation at high values of PFD, a more realistic estimate of PFD at which saturation occurs is about 30 mol m−2 day−1 , where the highest relative growth rate and nitrogen productivity were experimentally determined. No significant effect was observed because of day length differences between the present and previous experiments. 相似文献