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1.
Å. Franzén 《Zoomorphology》1984,104(3):140-146
Summary Differentiation of spermatids to mature spermatozoa in the bryozoan Tubulipora liliacea was studied by transmission electron microscopy. The spermatozoon of Tubulipora is of a filiform, modified type, and has evolved from the primitive type as an adaptation to a specialized biology of fertilization. The head of the spermatozoon consists of a small, conical acrosome capping an elongated, cylindrical, anteriorly tapering nucleus. A basal invagination in the nucleus contains the proximal portion of the axoneme and a dense attachment matrix. The flagellar axoneme has the typical 9+2 structure. Four elongated rodshaped mitochondria with typical cristae surround the axoneme in the cylindrical middle piece. Granular electron-dense material is accumulated in the form of four columns alternating with four long cylindrical mitochondria. The mitochondrial middle piece is separated externally from the tail region by an involution of the plasma membrane. The tail region contains a cytoplasmic sheath with accessory fibers surrounding the axoneme. Nine outer, coarse fibers extend posteriorly paralleling the nine doublets of the axoneme. The coarse fibers develop from electron-dense plate-like structures associated with the doublets of the axoneme. A characteristic feature in spermiogenesis is that spermatozoa develop in tetrads. There seem to be significant differences in spermatozoan ultrastructure between the three bryozoan classes Stenolaemata, Gymnolaemata, and Phylactolaemata. The differences indicate different lines of evolution of fertilization biology in these groups.Abbreviations used in the figures
a
acrosome
-
av
acrosomal vesicles
-
ax
axoneme
-
c
coarse fiber
-
d
electron dense rod
-
m
mitochondrion
-
mp
middle piece
- Scale
bars=0.5 m
-
mt
microtubule
-
n
nucleus
-
ne
nuclear envelope
-
p
nuclear protrusion
-
pm
plasma membrane
-
t
tail 相似文献
2.
Photo-CIDNP study of the interaction between the glucocorticoid receptor DNA-binding domain and glucocorticoid response elements 总被引:1,自引:0,他引:1
E. Kellenbach T. Härd R. Boelens K. Dahlman J. Carlstedt-Duke J. -Å. Gustafsson G. A. van der Marel J. H. van Boom B. Maler K. R. Yamamoto R. Kaptein 《Journal of biomolecular NMR》1991,1(1):105-110
Summary Photo-CIDNP studies were performed on two protein fragments that both contain the double zinc-finger DNA-binding domain of the glucocorticoid receptor. In the absence of DNA, Tyr452 and Tyr474 are polarised in both fragments while Tyr497 is not. Addition of a palindromic glucocorticoid response element (GRE) results in the suppression of Tyr474 polarization while the polarization of Tyr452 is unaffected. The same result is observed upon adding a half GRE to the protein fragment indicating that the suppression of Tyr474 polarization is not due to protein-protein contacts but to interaction with DNA. 相似文献
3.
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5.
Investigations were carried out in six forest types in areas surrounding two Swedish nuclear power plants (Forsmark and Laxemar). The aim of the investigation was to determine the spatial distribution of fine-root biomass (live), necromass (dead) and standing crop (live + dead) and to test the use of the live/dead ratio as a vitality criterion. Soil cores were taken to depths with insignificant amounts of roots. The total amount of fine-root biomass (<1 mm in diameter) of tree species in the soil profile was 267, 317 and 235 g m?2 for the Forsmark and 137, 371 and 50 g m?2 for the Laxemar sites. The related necromass was 119, 226 and 184 g m?2 and 87, 245 and 271 g m?2. The biomass in the humus layer was 47, 7 and 48% for the Forsmark and 34, 26 and 7% for the Laxemar sites, as a percentage of the total live + dead fine roots in the soil profile. The related necromass in the humus layer was 13, 2 and 30% for the Forsmark and 13, 2 and 28% for the Laxemar sites. The live/dead ratio decreased with depth for both tree— and field-layer species and seems to be a most powerful vitality criterion of fine roots. 相似文献
6.
We report the first study with the aim to estimate heritability in a wild population, a nest box breeding population of blue tits. We estimated heritability as well as genetic and phenotypic correlations of resting metabolic rate (RMR), body mass and tarsus length with an animal model based on data from a split cross‐fostering experiment with brood size manipulations. RMR and body mass, but not tarsus length, showed significant levels of explained variation but for different underlying reasons. In body mass, the contribution to the explained variation is mainly because of a strong brood effect, while in RMR it is mainly because of a high heritability. The additive variance in RMR was significant and the heritability was estimated to 0.59. The estimates of heritability of body mass (0.08) and tarsus length (0.00) were both low and based on nonsignificant additive variances. Thus, given the low heritability (and additive variances) in body mass and tarsus length the potential for direct selection on RMR independent of the two traits is high in this population. However, the strong phenotypic correlation between RMR and mass (0.643 ± 0.079) was partly accounted for by a potentially strong, although highly uncertain, genetic correlation (1.178 ± 0.456) between the two traits. This indicates that the additive variance of body mass, although low, might still somewhat constrain the independent evolvability of RMR. 相似文献
7.
Å. Lothigius Å. Sjöling A.‐M. Svennerholm I. Bölin 《Journal of applied microbiology》2010,108(4):1441-1449
Aims: In this study, the main objective was to verify the hypothesis of induction of ‘viable but non‐culturable’ (VBNC) forms of enterotoxigenic Escherichia coli (ETEC) during incubation in water. Methods and Results: Six clinically isolated ETEC strains were studied. Viable counts showed culturable ETEC bacteria for up to 3 months in freshwater but only two out of six strains were culturable in seawater at this time point. Although the bacterial cells remained intact, no production or secretion of heat‐labile (LT) or heat‐stable (ST) enterotoxins was observed using GM1‐ELISA methods. However, genes encoding ETEC toxins (STh and LT), colonization factors (CS7 and CS17), gapA and 16S RNA were expressed during 3 months in both sea water and freshwater microcosms as determined by real‐time RT‐PCR on cDNA derived from the bacteria. Conclusions: Clinically isolated ETEC strains can survive for long periods in both sea water and freshwater. The bacterial cells remain intact, and the gene expression of virulence genes and genes involved in metabolic pathways are detected after 3 months. Significance and Impact of the Study: These results indicate that ETEC bacteria can enter a VBNC state during stressful conditions and suggest that ETEC has the potential to be infectious after long‐term incubation in water. 相似文献
8.
The bivalve Pseudopythina macrophthalmensis (Galeommatoidea) is a commensal with the crab Macrophthalmus convexus (Ocypodidae) in Okinawa Prefecture, Japan. It is a protandric hermaphrodite which incubates the 65-μm large ova in the suprabranchial
cavity. The species produces two types of sperm, which were studied with the electron microscope. The euspermatozoon has an
elongate 2.8-μm-long, pointed acrosome, a slender 12- to 13-μm-long nucleus and a middlepiece containing several closely packed
mitochondria arranged as a 5.5- to 6.0-μm-long sheath around the basis of the flagellum. The paraspermato- zoon is vermiform,
220-μm-long and up to 5-μm-broad. Anteriorly there is a ca 7-μm-long bullet-shaped acrosome followed by a subcylindrical 3.0-
to 4.7-μm-long nucleus. Adjacent to the nucleus occurs a bundle of 26–42 40-μm-long flagella. The cytoplasm is packed with
spherical lipid droplets and ovoid granules of unknown composition. Sperm of both types aggregate to form spermatozeugmata,
which were found in the posterior mantle cavity or in paired seminal receptacles. Within the receptacles the euspermatozoa
dissociate themselves from the spermatozeugma and become attached to the epithelial lining of the receptacle whereas the paraspermatozoa
presumably disintegrate. The possible significance of the two types of sperm is discussed in the light of their presumed functions
in gastropods.
Accepted: 9 November 2000 相似文献
9.
Optimization of sulphide production in an anaerobic continuous biofilm process with sulphate reducing bacteria 总被引:1,自引:0,他引:1
Different biofilm reactors for sulphide production by sulphate reducing bacteria were compared in a packed bed reactor and in two suspended carrier biofilm reactors. Lactate was used as carbon source in the experiments. The process was reversibly inhibited by free sulphide at 14 mM. The packed bed reactor was more efficient and less sensitive to changes. The maximum load in the system was 5.3 g sulphate/l.d. 相似文献
10.