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We examined factors affecting the duration of the staminate and pistillate phases in the protandrous flowers of Campanula rapunculoides L. (Campanulaceae). Under conditions of natural pollinator visitation, flowers experiencing low rates of pollen removal lasted significantly longer than flowers that had faster rates of pollen removal. Experimental manipulations showed that low levels of pollen removal resulted in extension of the staminate phase. Hand-pollinations in which we varied the amount and source of pollen showed that when the number of fertilized ovules within an ovary is low, senescence of the flower is delayed, resulting in extension of the pistillate phase. We also report on pollinator foraging patterns within the vertical inflorescences of C. rapunculoides and the limiting factor for seed set in this population. The results are relevent to recent suggestions that floral characters often serve to reduce interference between the sexual functions in cosexual plants. 相似文献
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The scale up of earlier work from these laboratories using the enzyme serinehydroxymethyltransferase has resulted in the use of this enzyme for the synthesis of 2-amino-3-hydroxy-1,6-hexanedicar☐ylic acid (7) on a preparative scale. This compound, which has been barely described in the literature, is potentially useful for the synthesis of carbocyclic β-lactams and carbocyclic nucleosides. 相似文献
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Deborah M. Briercheck Timothy J. Allison John P. Richardson Jeffery F. Ellena Todd C. Wood Gordon S. Rule 《Journal of biomolecular NMR》1996,8(4):429-444
Summary Protein fragments containing the RNA-binding domain of Escherichia coli rho protein have been over-expressed in E. coli. NMR spectra of the fragment containing residues 1–116 of rho protein (Rho116) show that a region of this protein is unfolded in solution. Addition of (dC)10 to this fragment stabilizes the folded form of the protein. The fragment comprising residues 1–130 of rho protein (Rho130) is found to be stably folded, both in the absence and presence of nucleic acid. NMR studies of the complex of Rho 130 with RNA and DNA oligonucleotides indicate that the binding-site size, affinity, and specificity of Rho 130 are similar to those of intact rho protein; therefore, Rho 130 is a suitable model of the RNA-binding domain of rho protein. NMR line widths as well as titration experiments of Rho130 complexed with oligonucleotides of various lengths suggest that Rho130 forms oligomers in the presence of longer oligonucleotides. 1H, 15N and 13C resonance assignments were facilitated by the utilization of two pulse sequences, CN-NOESY and CCH-TOCSY. The secondary structure of unliganded Rho130 has been determined by NMR techniques, and it is clear that the RNA-binding domain of rho is more structurally similar to the cold shock domain than to the RNA recognition motif.Abbreviations Rho116, Rho130
protein containing the first 116 (130) residues of rho
- CSD
cold shock domain
- RRM
RNA recognition motif
- RBD
RNA-binding domain
- IPTG
isopropyl -D-thiogalactopyranoside
- EDTA
ethylenediaminetetraacetic acid
- NOE
nuclear Overhauser enhancement 相似文献
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David M. Richardson Richard M. Cowling Byron B. Lamont 《Biodiversity and Conservation》1996,5(9):1035-1046
This paper explores the determinants of extinction of endemic plant taxa in mediterranean-climate regions in South Africa and southwestern Australia. Major threats to biodiversity in these areas include agriculture, deforestation, fragmentation, invasive alien organisms and urbanization. Case studies from the two regions show that synergisms between factors can lead to discontinuous, or non-linear, responses that have increased extinction rates (or threaten to) beyond predictions based on simple deterministic processes. 相似文献
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