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811.
812.
813.
Osedax is a genus of siboglinid annelids in which the females live on dead vertebrate bones on the seafloor. These females have a posterior end that lies within the bone and contains the ovarian tissue, as well as the “roots” involved with bone degradation and nutrition. The males are microscopic and live as “harems” in the lumen of the gelatinous tube that surrounds the female trunk, well away from the ovary. Females are known to spawn fertilized primary oocytes, suggesting internal fertilization. However, little is known about sperm transfer, sperm storage, or the location of fertilization, and the morphology of the female reproductive system has not been described and compared with the reproductive systems of other siboglinids. A 3D‐reconstruction of the ovisac of Osedax showed ovarian tissue with multiple lobes and mature oocytes stored in a “uterus” before being released through the single oviduct. The oviduct emerges as a gonopore on the trunk and travels along the trunk to finally open to the seawater as a thin cylindrical tube among the crown of palps. Light and transmission electron microscopy of mature Osedax sperm revealed elongate heads consisting of a nucleus with helical grooves occupied by mitochondria. In contrast to other Siboglinidae, Osedax sperm are not packaged into spermatophores or spermatozeugmata, and Osedax females lack a discrete region for sperm storage. Transmission electron microscopy and fluorescence microscopy allowed detection of sperm associated with ovarian tissue of the female ovisac of four different Osedax species. This provides the first evidence for the site of internal fertilization in Osedax. A heart body was found in the circulatory system, as seen in other siboglinids and some other annelids. The possible presence of nephridia in the anterior ovisac region was also documented. These morphological features provide new insights for comparing the regionalization of Osedax females in relation to other siboglinids. 相似文献
814.
Sigrid Liede-Schumann Stefan Dötterl Margit Gebauer Ulrich Meve 《Organisms Diversity & Evolution》2013,13(1):15-31
One hundred and thirty-seven accessions of Cynanchum viminale and its relatives, formerly known as Sarcostemma, were studied using randomly amplified polymorphic DNA (RAPD). A fingerprinting technique was used because sequencing had failed to differentiate between morphologically separable groups. Chromosome counts were conducted to establish the ploidy level of the accessions. The banding patterns resulting from RAPD analysis were evaluated with Canonical Analysis of Principal Coordinates, Permanova and neighbour-joining. A strong geographic component was found in the structure of the group. Taxa considered species or subspecies based on morphology often formed coherent groups. The data are interpreted to reflect at least two cycles of diversification: the first one from Madagascar and the second one most likely from the East African–Arabian region, reaching Madagascar again. In mainland Africa, polyploidisation has occurred several times. 相似文献
815.
Cane Toads (Rhinella marina, formerly Bufo marinus) in restoration sites on the Atherton Tableland in NE Australia consumed invertebrates belonging to 11 different taxa with ants being the most abundant prey item. Principal component analyses showed that the composition of invertebrates in Cane Toad diet is largely a reflection of invertebrates found in pitfall and leaf litter samples suggesting that the species is an indiscriminant feeder. However, pitfall samples contained more Collembola and Isopoda than were found in Cane Toad stomachs. The Cane Toad may benefit from restoration management practices by utilizing food resources enhanced by mulching and providing microhabitats (e.g. rock piles, logs) as shelter. While further studies would be needed to test this practitioners working in areas where the Cane Toad is problematic may consider trade‐offs between attracting invertebrates and Cane Toads by monitoring provided microhabitat features. 相似文献
816.
817.
Ammonium uptake in Lemna gibba G 1, related membrane potential changes, and inhibition of anion uptake 总被引:6,自引:0,他引:6
Wolfram R. Ullrich Marie Larsson Carl-Magnus Larsson Sigrid Lesch Anton Novacky 《Physiologia plantarum》1984,61(3):369-376
In N-starved (?N) fronds of Lemna gibba L. G 1, NH4+ uptake rates were several-fold those of NO3?-supplied (+N) fronds. NO3?, uptake in +N-plants was slow and not inhibited by addition of NH4+. However, in ?N-plants with higher NO3? and still higher NH4+ uptake rates, addition of NH4+ immediately reduced the NO3? uptake rates to about one third until the NH4+ was consumed. The membrane potential (Em) decreased immediately upon addition of NH4+ in all fronds, but whereas depolarisation was moderate and transient in +N-plants, it was strong, up to 150 mV, in N-starved plants, where Em remained at the level of the K+ diffusion potential (ED) until NH4+ was removed. In N-starved plants NH4+ uptake and membrane depolarisation showed the same concentration dependence, except for an apparent linear component for uptake. Phosphate uptake was inhibited by NH4+ similarly to NO3? uptake, but only in P- and N-starved plants, not after mere P starvation. Influx of NO3? and H2PO 4? into the negatively charged cells of Lemna is mediated by anion/H+ cotransport, but NH4+ influx can follow the electrochemical gradient. Its saturating component may reflect a carrier-mediated NH4+ uniport, the linear component diffusion of NH4+ or NH3. Inhibition of anion/H+ cotransport by high NH4+ influx rates may be due to loss of the proton-driving force, Δμ?H+, across the plasmalemma. Reversible inhibition by NH4+ of the H+ extrusion pump may contribute to the finding that Δμ?H+ cannot be reconstituted in the presence of higher NH4+ concentrations. 相似文献
818.
Jan Bauer Sigrid R. Ruuls Ingeborg Huitinga Christine D. Dijkstra 《The Histochemical journal》1996,28(2):83-97
Summary In this review the role of various subpopulations of macrophages in the pathogenesis of experimental autoimmune encephalomyetitis
is discussed. Immunohistochemistry with macrophage markers shows that in this disease different populations of macrophages
(i.e. perivascular cells, microglia and infiltrating blood-borne macrophages) are present in the central nervous system. These
subpopulations partially overlap in some functional activity while other activities seem to be restricted to a distinct subpopulation,
indicating that these subpopulations have different roles in the pathogenesis of encephalomyelitis. The studies discussed
in this review reveal that immunocytochemical and morphological studies, combined with new techniques such asin situ nick translation and experimental approaches like the use of bone marrow chimeras and macrophage depletion techniques, give
valuable information about the types and functions of cells involved in central nervous system inflammation. The review is
divided in three parts. In the first part the experimental autoimmune encephalomyelitis model is introduced. The second part
gives an overview of the origin, morphology and functions of the various subpopulations. In the third part the role of these
subpopulations is discussed in relation to the various stages (i.e. preclinical, clinical and recovery) of the experimental
disease. 相似文献
819.
Sigrid A. Lehnert Kate J. Wilson Keren Byrne Stephen S. Moore 《Marine biotechnology (New York, N.Y.)》1999,1(5):465-476
Expressed sequence tag data were generated from complementary DNA libraries created from cephalothorax, eyestalk, and pleopod
tissue of the black tiger shrimp (Penaeus monodon). Significant database matches were found for 48 of 83 nuclear genes sequenced from the cephalothorax library, 22 of 55 nuclear
genes from the eyestalk library, and 6 of 13 nuclear genes from the pleopod library. The putative identities of these genes
reflected the expected tissue specificity. For example, genes for digestive enzymes were identified from the cephalothorax
library and genes involved in the visual and neuroendocrine system from the eyestalk library. A few sequences matched anonymous
EST or genomic sequences, and others contained mini-satellite or microsatellite repeat sequences. The remainder, 31 from the
cephalothorax library, 25 from the eyestalk library, and 5 from the pleopod library, were sequences of high nucleotide complexity
with no matches in any database searched and thus may represent novel genes.
Received February 12, 1999; accepted April 13, 1999 相似文献
820.
Porphyrin methyl esters and the isomers of uroporphyrin and heptacarboxylic porphyrin were separated by high-performance liquid chromatography. Isocoproporphyrin was also separated from coproporphyrin. By slight modifications to the solvent mixture, the separation of all biological polycarboxylic porphyrins was achieved. These separations were made possible through the high efficiency of 10- or 5-μm particle-size Radial-PAK cartridges, which have been used in the separation of porphyrins in various excreta and tissues in a number of porphyrias. 相似文献