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Mate calling is a prominent reproductive behavior of male South African clawed frogs. Calls consist of alternating slow- and fast-amplitude-modulated trills. Each trill is made up of a series of clicks. The effects of administration of exogenous gonadotropin and androgen on mate calling were studied in male Xenopus laevis. Males were paired with unreceptive female frogs to elicit maximal calling. The amount of time each animal spent calling during the testing period, the peak fundamental frequency of the calls, the rate of calling, and the interclick interval (ICI, a measure of the temporal patterning of the calls) were measured in intact, castrated, and hormone-replaced frogs. Injection of human chorionic gonadotropin (HCG) into intact frogs increased the amount of time spent calling and the ICI relative to measures taken after water injection. Castrated males did not call even when given HCG. Testosterone and dihydrotestosterone treatment reinstated calling in castrates and increased circulating levels of androgens. When androgen-replaced castrated males were injected with HCG, the amount of time spent calling increased and approached levels of intact, HCG-injected males. The above results suggest that androgens are necessary for the production of calls. Gonadotropins appear to play an important role in mate calling, a role at least partly independent of effects on testicular androgen synthesis. 相似文献
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Seasonally fluctuating bark proteins are a potential form of nitrogen storage in three temperate hardwoods 总被引:8,自引:0,他引:8
The inner bark tissues of three temperate hardwoods contain specific proteins which undergo seasonal fluctuations. Increases in particular proteins, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, occur within the bark of several Acer, Populus and Salix spp. during late summer and early autumn. These proteins are abundant in the bark throughout the winter and their levels decline the following spring. Light and electron microscopy showed that the parenchyma cells of the inner bark are packed with spherical organelles throughout the overwintering period. These organelles are rich in protein and analogous to protein bodies found in cells of mature seeds. The protein bodies of the parenchyma cells are replaced by large central vacuoles during spring and summer, presumably as a result of the mobilization of the storage protein and fusion of the protein bodies. The high levels of specific proteins in inner bark tissues and the presence of protein bodies within the parenchyma cells indicate that the living cells of the bark act as a nitrogen reserve in overwintering temperate hardwoods.Abbreviations FW
fresh weight
- kDa
kilodalton
- M
r
relative molecular mass 相似文献
596.
Tissues from the aquatic macrophyte species Scirpus subterminalis, Najas flexilis, Ceratophyllum demcrsum, Potamogeton zosteriformis, and Nuphar advena contain cAMP in quantities similar to those reported in algae. Scirpus, Najas , and Ceratophyllum released cAMP into the extracellular media in quantities which varied interspecifically and intraspecifically in differing media. Macrophytic release of cAMP may be an important source of dissolved cAMP in lakewater. 相似文献
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H. J. N. SCHOENMAKERS CH. G. VAN BOHEMEN S. J. DIELEMAN 《Development, growth & differentiation》1981,23(2):125-135
Oocyte diameters and their frequency distribution, and various other data determined for the oestradiol-17 β treated female specimens of Asterias rubens proved to be significantly different from those for the control animals. The maturation index of the treated animals is 2.4, that of the control animals 1.4. Since the treated animals show a greater heterogeneity in development than the control animals, and because the diameter of the smallest oocytes is the same for both treated and control animals, a threshold size of the oocytes may be required before oocyte growth can be stimulated by oestradiol-17β, and before substances originating in the pyloric caeca are incorporated into the oocytes. Oestradiol-17β treatment caused a tenfold increase of the oestrone level in the ovaries, whereas a non-significant increase was observed in the pyloric caeca. This may indicate that in vivo oestradiol-17β is converted into oestrone in the ovaries but not in the pyloric caeca. 相似文献
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A novel method is described for the cyclization of peptides--or segments of polypeptides--which requires a free N-terminal alpha-amino group and a distal amino acid residue containing a nucleophilic side chain. The reaction is conducted in two steps, both in the aqueous phase. The first step involves acylation of the N-terminal alpha-amino group with iodoacetic anhydride at pH 6. This acylation reaction has greater than 90% specificity for peptide alpha-amino groups and gives no alkylation of Arg, His, Lys or Met by the iodoacetate side product (R. Wetzel et al., Bioconjugate Chem., 1, 114-122, 1990). In the second step, the acylation reaction mixture or the isolated iodoacetyl-peptide is incubated at room temperature to give the cyclic peptide formed by reaction of the nucleophilic side chain with the iodoacetyl moiety. The pH dependence of the cyclization reaction by Met, Lys, Arg or His is consistent with the pKa of the nucleophilic side chain. Thus, peptides containing Met plus other nucleophilic amino acids should preferentially cyclize via Met at low pH. In this paper, preparation of cyclic peptides containing 3-6 amino acids is described; the full range of ring sizes and sequences which can undergo this cyclization has not been further explored. Preliminary results suggest that this method is also fairly general with respect to the amino acid sequence being cyclized. The reaction appears to be particularly suited for cyclization via Lys and Met side chains. All of the cyclized products are sufficiently stable for many biological applications.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献