PATTERNS OF ALLOZYME VARIATION IN DIPLOID AND TETRAPLOID CENTAUREA JACEA AT DIFFERENT SPATIAL SCALES

Abstract.— The extent and spatial patterns of genetic variation at allozyme markers were investigated within and between diploid and autotetraploid knapweeds (Centaurea jacea L. sensu lato, Asteraceae) at contrasted geographic scales: (1) among populations sampled from a diploid‐tetraploid contact zone in the northeastern part of the Belgian Ardennes, and (2) within mixed populations from that zone where diploids and tetraploids coexist. Our data were also compared with a published dataset by Sommer (1990) describing allozyme variation in separate diploid and tetraploid knapweeds populations collected throughout Europe. Genetic diversity was higher in tetraploids. In the Belgian Ardennes and within the mixed populations, both cytotypes had similar levels of spatial genetic structure, they were genetically differentiated, and their distributions of allele frequencies were not spatially correlated. In contrast, at the European scale, diploids and tetraploids did not show differentiated gene pools and presented a strong correlation between their patterns of spatial genetic variation. Numerical simulations showed that the striking difference in patterns observed at small and large geographic scales could be accounted for by a combination of (1) isolation by distance within cytotypes; and (2) partial reproductive barriers between cytotypes and/or recurrent formation of tetraploids. We suggest that this may explain the difficulty of the taxonomic treatment of knapweeds and of polyploid complexes in general.     

ULTRASTRUCTURAL OBSERVATIONS ON THE SPERMATOZOA OF PLEUROTOMARIA AFRICANA TOMLIN (GASTROPODA)

Spermatozoa from formalin/alcohol preserved testes of Pleuotomariaafricana Tomlin are examined using transmission electron microscopy.These spermatozoa possess the following features: (1) an acro-somalvesicle (acrosomal cone), 1 µm long and deeply invaginated;(2) an axial rod occupying the inva-gination of the acrosomalvesicle; (3) a cylindrical nucleus (length 4 µm, maximumdiameter 1.5 µm) exhibiting occasional irregular cavities;(4) shallow imaginations at anterior and posterior extremitiesof the nucleus; (5) four or five spherical mitochondria pressedinto posterior indentations of the nucleus, and clustered aroundthe proximal and distal centrioles; (6) a single flagellum continuouswith the distal cen-triole and (7) a satellite fibre—densering complex associated with the distal centriole and attachedflagellum. Substructure of the centrioles could not be determined,but presumably both are composed of triplets. Spermatozoa ofP. africana are simple in structure (as expected of an externallyfertilizing species) and, among the Gastropoda, resemble spermatozoaof some trochids more so than those of other pleurotomaroideans(Haliotidae, Scissurellidae) or the Fissurelloidea. The primitiveposition of the Ple-urotomariidae within the Prosobranchia issupported by sperm morphology ^*Present address: Department of Zoology, University of Queensland,St. Lucia, 4067 Queensland, Australia (Received 30 December 1987; accepted 11 January 1988)     

非洲蝼蛄(Gryllotalpa africana Palisot de Beauvois)的鸣声结构及声引诱

本工作对北京地区非洲蝼蛄的鸣声结构作了详细分析;明确了在声通讯中起重要作用的参量并以其引诱力最强的召唤信号进行了声引诱实验。在成虫活动高峰期——晚间2小时38分钟内,平均一个声诱捕器捕获蝼蛄556只,最多的一个诱捕922只。     

STRUCTURE OF THE EGG-SHELL OF CULEX PIPIENS AND MANSONIA AFRICANA (CULICIDAE, DIPTERA)

Eggs of Culex pipiens L. are laid in rafts on the surface of still or slow moving water, whereas those of Mansonia africana (Theobold) are deposited beneath tho surface of the water on the undersides of floating leaves (Laurence & Smith 1958; Laurence 1959). The eggs of both species are surrounded by air, those of Culex pipiens are in direct contact with the external atmosphere, whereas those of Mansonia africana are partially surrounded by a bubble of air trapped between them. The anterior onds of the eggs of Mansonia africana project through the bubble of air into the surrounding water. This bubble of air is only found around living eggs and disappears if tho eggs die and shortly before they hatch. Iyengar (1935) has shown that the eggs of Ficalba minima Theo. although often deposited on the same leaf as those of Mansonioides , are laid above the water line and resemble in structure those of Culex and Coquillettidia . The structure of the egg-shell of both Culez pipiens and Mansonia africana is described and discussed.     

FOLIAR NECTARIES OF UNUSUAL STRUCTURE IN LEONARDOXA AFRICANA (LEGUMINOSAE), AN AFRICAN OBLIGATE MYRMECOPHYTE

Extrafloral nectaries of an African myrmecophyte, Leonardoxa africana (Baill.) Aubr., are disc-shaped, non-vascularized, embedded in the leaf mesophyll, and have a tiny neck extending to the abaxial leaf surface. These structural features differ from those found in other members of the Leguminosae, and represent an unusual type among flowering plants. These embedded foliar nectaries apparently have an energetic advantage over external nectaries and their presence supports the idea of independent and repeated evolution of nectaries in the legume family.     

Positions 13 and 914 in Escherichia coli 16S ribosomal RNA are involved in the control of translational accuracy.

Using a conditional expression system with the temperature-inducible lambda PL promoter, we previously showed that the single mutations 13U-->A and 914A-->U, and the double mutation 13U-->A and 914A-->U in Escherichia coli 16S ribosomal RNA impair the binding of streptomycin (Pinard et al., The FASEB Journal, 1993, 7, 173-176). In this study, we found that the two single mutations and the double mutation increase translational fidelity, reducing in vivo readthrough of nonsense codons and frameshifting, and decreasing in vitro misincorporation in a poly(U)-directed system. Using oligodeoxyribonucleotide probes which hybridize to the 530 loop and to the 1400 region of 16S rRNA, two regions involved in the control of tRNA binding to the A site, we observed that the mutations in rRNA increase the binding of the probe to the 530 loop but not to the 1400 region. We suggest that the mutations at positions 13 and 914 of 16S rRNA induce a conformational rearrangement in the 530 loop, which contributes to the increased accuracy of the ribosome.     

微RNA Cre-miR914参与调控衣藻对高温胁迫的适应过程

高温胁迫是生物所面临的常见环境胁迫,因此在长期进化中生物逐渐进化出了对高温胁迫的高效适应能力.目前,有关藻类对高温胁迫的适应机制研究主要集中在生理调控及其相关的编码基因调控方面,而有关非编码基因对高温适应的调控尚无报道.在前期研究中,我们通过对衣藻细胞的定量PCR筛选和生物信息学分析发现,在多种胁迫处理后Cre-miR914表达下调且其靶基因有可能是RPL18,但对它们的作用却不清楚.本研究中利用生物信息学结合降解组测序确定了Cre-miR914的靶基因是RPL18,接着利用定量PCR验证Cre-miR914及其靶基因的表达情况,发现Cre-miR914表达在高温处理后明显下调,而RPL18表达明显上调,同时通过构建Cre-miR914过表达株和靶基因RPL18过表达株,结合高温胁迫处理和抗性表型研究,发现Cre-miR914过表达明显降低衣藻对抗高温胁迫能力,而靶基因RPL18过表达提高了衣藻对抗高温胁迫能力.本研究发现了一个microRNA参与调控藻类高温适应过程的分子机制,即衣藻通过调控Cre-miR914及其靶基因RPL18表达参与了的高温胁迫适应过程.     

GmPep914, an eight-amino acid peptide isolated from soybean leaves, activates defense-related genes

Only a handful of endogenous peptide defense signals have been isolated from plants. Herein, we report a novel peptide from soybean (Glycine max) leaves that is capable of alkalinizing the media of soybean suspension cells, a response that is generally associated with defense peptides. The peptide, DHPRGGNY, was synthesized and found to be active at 0.25 nM and requiring only 5 to 10 min to obtain a maximal pH change. The peptide is located on the carboxy-terminal end of a 52-amino acid precursor protein (Glyma12g00990) deduced from the soybean genome project. A search of the soybean databank revealed a homolog (Glyma09g36370) that contained a similar peptide, DLPRGGNY, which was synthesized and shown to have identical activity. The peptides, designated GmPep914 (DHPRGGNY) and GmPep890 (DLPRGGNY), were capable of inducing the expression of both Glyma12g00990 (GmPROPEP914) and Glyma09g36370 (GmPROPEP890) in cultured soybean suspension cells within 1 h. Both peptides induced the expression of defense genes, including CYP93A1, a cytochrome P450 gene involved in phytoalexin synthesis, chitinaseb1-1, a chitinase involved in pathogen defense, and Glycine max chalcone synthase1 (Gmachs1), chalcone synthase, involved in phytoalexin production. Both GmPROPEP914 and GmPROPEP890 were highly expressed in the roots, relative to the aerial portions of the plant. However, treatment of the aerial portion of soybean plants with hormones involved in elicitation of defense responses revealed a significant increase in expression levels of GmPROPEP914 and GmPROPEP890. A search of gene databases revealed homologous sequences in other members of the Fabales and also in the closely related Cucurbitales but not in any other order of plants.