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1.
M.M. van Katwijk D. C. R. Hermus D.J. de Jong R. M. Asmus V.N. de Jonge 《Helgoland Marine Research》2000,54(2-3):117-128
A conceptual model is proposed, describing potential Zostera marina habitats in the Wadden Sea, based on reported data from laboratory, mesocosm and field studies. Controlling factors in the
model are dynamics, degree of desiccation, turbidity, nutrients and salinity. A distinction has been made between a higher
and a lower zone of potential habitats, each suitable for different morphotypes of Z. marina. The model relates the decline of Z. marina in the Wadden Sea to increased sediment and water dynamics, turbidity, drainage of sediments (resulting in increased degree
of desiccation) and total nutrient loads during the twentieth century. The upper and lower delineation of both the higher
and the lower zone of potential Z. marina habitats appear to be determined by one or a combination of several of these factors. Environmental changes in one of these
factors will therefore influence the borderlines of the zones. The lower zone of Z. marina will be mainly affected by increased turbidity, sediment dynamics, degree of desiccation during low tide and nutrient load.
The higher zone will be affected by increases in water and sediment dynamics, desiccation rates and nutrient loads. Potential
Z. marina habitats are located above approx. –0.80 m mean sea level (when turbidity remains at the same level as in the early 1990s)
in sheltered, undisturbed locations, and preferably where some freshwater influence is present. At locations with a high,
near-marine, salinity, the nutrient load has to be low to allow the growth of Z. marina. The sediment should retain enough water during low tide to keep the plants moist. Our results suggest that the return of
Z. marina beds within a reasonable time-scale will require not only suitable habitat conditions, but also revegetation measures, as
the changes in the environment resulting from the disappearance of Z. marina may impede its recovery, and the natural import of propagules will be unlikely. Furthermore, the lower zone of Z. marina may require a genotype that is no longer found in the Wadden Sea.
Received: 26 April 1999 / Received in revised form: 15 October 1999 / Accepted: 16 October 1999 相似文献
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Human erythrocyte and brain acetylcholinesterase are preferentially inhibited by the P(-)-isomers of C(+/-)P(+/-)-soman. The enzymes inhibited by the P(-)-isomers behave similarly with respect to oxime-induced reactivation and aging. HI-6 is the best reactivator for C(+)P(-)-soman-inhibited acetylcholinesterases. Oxime-induced reactivation of the C(-)P(-)-soman-inhibited acetylcholinesterases is much more difficult to achieve. 相似文献
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F F Smith J R Mertz I Krebs L L Tres C B Chae Z Zakeri J Engelhardt D Hoover M Tenniswood A L Kierszenbaum 《Molecular reproduction and development》1992,33(4):363-372
We have previously reported that a heterodimeric protein secreted by rat Sertoli cells is antigenically related to a protein associated with outer dense fibers of the sperm tail. Therefore, we have explored the possibility that Sertoli and spermatogenic cells express a similar gene encoding a homologous protein. A Sertoli cell heterodimeric protein cDNA probe recognizes specific mRNA in pachytene and round spermatids fractionated by centrifugal elutriation; however, this specific mRNA was less prominent than in cultured Sertoli cells. In agreement with these observations, in situ hybridization experiments show that Sertoli cells are predominantly engaged in active heterodimeric protein mRNA synthesis, while meiotic prophase spermatocytes and spermatids also show significant but less abundant specific mRNA. Immunoblotting experiments demonstrate that, while Sertoli cells synthesize a heterodimeric protein consisting of two disulfide-linked components with molecular masses of 45 and 35 kD, both primary spermatocytes and round spermatids synthesize single 30 kD monomers not associated by disulfide linkage but recognized by antisera to Sertoli cell heterodimeric protein. Immunoblotting and immunogold electron microscopic studies show that antisera to Sertoli cell heterodimeric protein recognize a protein associated with outer dense fibers. This immunoreactivity was abolished by a 5-min pronase treatment, without affecting the integrity of outer dense fibers. Results of this study and previous studies demonstrate that both Sertoli and spermatogenic cells express a similar gene and that an antigenically related product encoded by this gene becomes associated with outer dense fibers during their assembly at spermiogenesis. 相似文献
6.
Compression wood (CW) contains higher quantities of β-1-4-galactan than does normal wood (NW). However, the physiological
roles and ultrastructural distribution of β-1-4-galactan during CW formation are still not well understood. The present work
investigated deposition of β-1-4-galactan in differentiating tracheids of Cryptomeria japonica during CW formation using an immunological probe (LM5) combined with immunomicroscopy. Our immunolabeling studies clearly
showed that differences in the distribution of β-1-4-galactan between NW (and opposite wood, OW) and CW are initiated during
the formation of the S1 layer. At this stage, CW was strongly labeled in the S1 layer, whereas no label was observed in the S1 layer of NW and OW. Immunogold labeling showed that β-1-4-galactan in the S1 layer of CW tracheids significantly decreased during the formation of the S2 layer. Most β-1-4-galactan labeling was present in the outer S2 region in mature CW tracheids, and was absent in the inner S2 layer that contained helical cavities in the cell wall. In addition, delignified CW tracheids showed significantly more labeling
of β-1-4-galactan in the secondary cell wall, suggesting that lignin is likely to mask β-1-4-galactan epitopes. The study
clearly showed that β-1-4-galactan in CW was mainly deposited in the outer portion of the secondary cell wall, indicating
that its distribution may be spatially consistent with lignin distribution in CW tracheids of Cryptomeria japonica. 相似文献
7.
Leandro Neves Faria Marlon Gomes Da Rocha Quirijn De Jong Van Lier Derblai Casaroli 《Plant and Soil》2010,331(1-2):299-311
Correct modeling of root water uptake partitioning over depth is an important issue in hydrological and crop growth models. Recently a physically based model to describe root water uptake was developed at single root scale and upscaled to the root system scale considering a homogeneous distribution of roots per soil layer. Root water uptake partitioning is calculated over soil layers or compartments as a function of respective soil hydraulic conditions, specifically the soil matric flux potential, root characteristics and a root system efficiency factor to compensate for within-layer root system heterogeneities. The performance of this model was tested in an experiment performed in two-compartment split-pot lysimeters with sorghum plants. The compartments were submitted to different irrigation cycles resulting in contrasting water contents over time. The root system efficiency factor was determined to be about 0.05. Release of water from roots to soil was predicted and observed on several occasions during the experiment; however, model predictions suggested root water release to occur more often and at a higher rate than observed. This may be due to not considering internal root system resistances, thus overestimating the ease with which roots can act as conductors of water. Excluding these erroneous predictions from the dataset, statistical indices show model performance to be of good quality. 相似文献
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10.
J Chae M J Kim J H Goo S Collier D Gubb J Charlton P N Adler W J Park 《Development (Cambridge, England)》1999,126(23):5421-5429
The tissue polarity genes control the polarity of hairs, bristles and ommatidia in the adult epidermis of Drosophila. We report here the identification of a new tissue polarity gene named starry night (stan). Mutations in this essential gene alter the polarity of cuticular structures in all regions of the adult body. The detailed polarity phenotype of stan on the wing suggested that it is most likely a component of the frizzled (fz) pathway. Consistent with this hypothesis, stan appears to be downstream of and required for fz function. We molecularly cloned stan and found that it encodes a huge protocadherin containing nine cadherin motifs, four EGF-like motifs, two laminin G motifs, and seven transmembrane domains. This suggests that Stan functions in signal reception, perhaps together with Fz. 相似文献