鸡眼草水浸提液对4种草坪草的化感作用

为探讨鸡眼草(Kummerowia striata)不同部位、不同浓度水浸提液对高羊茅(Festuca arundinacea)、黑麦草(Lolium perenne)、狗牙根(Cynodon dactylon)、白三叶(Trifolium repens)等4种草坪草的化感效应和作用规律,采用培养皿纸床法,以蒸馏水为对照,研究鸡眼草剪碎的植株、未剪碎的植株、叶、茎、根、地上部分0.012 5、0.025、0.05 g/mL 3个不同浓度的水浸提液对高羊茅、黑麦草、狗牙根、白三叶的种子发芽率、发芽速率、幼根长、幼苗高的化感作用。结果表明,鸡眼草水浸提液对高羊茅、黑麦草、狗牙根、白三叶4种受体植物种子的萌发及幼苗生长均有较强的化感抑制作用,且对种子发芽率作用强弱顺序为:狗牙根白三叶黑麦草高羊茅,对种子发芽速率作用强弱顺序为:黑麦草高羊茅狗牙根白三叶,对幼苗苗高作用强弱顺序为:黑麦草白三叶狗牙根高羊茅,对幼苗根长作用强弱顺序为:白三叶黑麦草狗牙根高羊茅。对4种受体植物的综合化感效应以高羊茅最弱,黑麦草、狗牙根、白三叶较为相近。4种受体植物所受到的抑制作用均随着水浸提液浓度的增加而增强,在同一浓度不同部位水浸提液处理下,叶、整株(剪碎)水浸提液对4种受体植物抑制作用比根、茎、整株(未剪碎)及地上部分水浸提液强。高羊茅、黑麦草、狗牙根3种草坪草受0.05 g/mL鸡眼草叶水浸提液的化感抑制作用最强,白三叶则受0.05 g/mL鸡眼草整株(剪碎)水浸提液的化感抑制作用最强。     

假臭草水浸提液对4种作物的化感作用

【背景】假臭草是近几年来入侵我国南方的外来杂草,目前已成功侵占海南、福建、广东等省沿海的大部分果园、草地、农田等农业生态系统,给当地农业生产造成极大的危害。【方法】采用室内生物测定方法研究不同浓度的假臭草水浸提液(0.010、0.025、0.050 g·m L~(-1))对4种作物(西瓜、水稻、萝卜和辣椒)种子萌发和幼苗生长的化感作用。【结果】各浓度的假臭草水浸提液对4种作物种子萌发和幼苗生长都有较强的化感作用,并且随着浸提液浓度的增大,化感效应显著增强。当浓度为0.050 g·m L~(-1)时,4种受体作物的化感综合效应顺序为西瓜萝卜水稻辣椒。【结论与意义】明确假臭草对不同供试作物的化感作用,能够为该入侵杂草的科学防治提供理论依据。     

入侵植物北美车前和野胡萝卜种内及种间的化感作用

当前入侵植物种类和入侵范围均日益扩大,而多种入侵植物共同入侵同一生境的概率也逐渐增加。为探讨这些入侵植物种内和种间的化感作用以及化感作用对其竞争能力的影响,本研究以北美车前(Plantago virgica)和野胡萝卜(Daucus carota)为例,采用室内生物学测定法,分析了2种植物不同器官(根、茎或花序轴、叶)、不同浓度(CK、0.005、0.01和0.05 g·mL^-1)的水浸提液培养对其自身和对方种子萌发和幼苗生长的影响。结果表明,浸提液浓度对2种入侵植物种子萌发和幼苗生长的影响最大,且浓度、器官及物种之间存在显著交互作用。2物种各器官各浓度浸提液对二者种子萌发总体表现为抑制;中低浓度浸提液对同种植物幼苗生长有一定促进作用;高浓度浸提液尤其是野胡萝卜叶浸提液对二者种子萌发与幼苗生长均有显著抑制作用。综合化感效应指数表明,浸提液浓度越高抑制作用越强,地上部分化感效应强于地下,且野胡萝卜对北美车前的种间化感作用最强。由此可见,种内和种间化感作用是入侵植物在相同入侵地相互竞争的重要方式。     

9种植物水浸提液对空心莲子草的化感作用

【背景】空心莲子草是难以防除的恶性入侵杂草,因此,探索高效无毒的化感防治方法具有重要意义。【方法】利用水浸提法研究了博落回、苦瓜、樟树、柳杉、凤尾蕨、柑橘、夹竹桃、洋葱及大蒜9种植物不同器官对空心莲子草的化感作用。【结果】与对照相比,博落回叶、苦瓜果肉与种子、凤尾蕨、樟树叶和柳杉叶的水浸提液对空心莲子草具有较强的化感作用,主要表现为空心莲子草叶片数和茎节数减少,株高与生物量的增长受到抑制。【结论与意义】不同植物水浸提液对空心莲子草的化感作用有所差异。本研究为利用植物的化感作用控制空心莲子草提供了依据。     

羽枝青藓和瘤柄匐灯藓对入侵植物种子萌发和幼苗生长的影响

入侵植物会通过化感作用等手段抑制本地种的生存繁衍,但本土植物尤其是地被层的藓类植物对入侵植物有何影响尚不清楚。本文以本土羽枝青藓和瘤柄匐灯藓为供体材料,以恶性入侵杂草稗草和野胡萝卜为受试材料,从藓丛结构特征和化感作用角度探究藓类植物对入侵植物种子萌发和幼苗生长的影响。结果表明: 2种入侵植物种子落入藓丛后其发芽率、发芽势和发芽指数均受到显著抑制,抑制效果为藓丛上部>藓丛下部>无藓丛。稗草种子落入藓丛下部会显著影响其根长和根芽比。施加藓类浸提液均显著降低2种入侵植物的发芽率、发芽势及发芽指数,但呈现不同的浓度效应。施加浸提液在一定程度上增加了稗草幼苗芽长、根长和根芽比,但对野胡萝卜无明显的规律性影响。藓类植物对2种入侵植物种子萌发和幼苗生长的化感综合效应均表现为抑制作用,其中,野胡萝卜的敏感性大于稗草,且高浓度下更加明显。可见,藓类植物对入侵植物种子萌发和幼苗生长具有一定抑制作用。     

入侵植物香丝草水浸提液对蚕豆和玉米根尖染色体行为的影响

以采自农田中自然生长的植物群落中的香丝草为供体,以典型的双子叶植物蚕豆和典型的单子叶植物玉米的幼苗为受体,运用根尖微核试验和染色体畸变试验,研究了香丝草的根、茎、叶和幼果4种器官水浸提液对受体的遗传毒性。结果表明:(1)在香丝草不同器官水浸提液作用下,蚕豆和玉米根尖细胞的有丝分裂各时期均受到明显影响,细胞中出现了微核、染色体桥、染色体断片、染色体环、染色体粘连及染色体滞后等多种染色体畸变。(2)香丝草各器官水浸提液对蚕豆幼苗根尖细胞分裂的抑制作用明显大于玉米。(3)香丝草各器官水浸提液对蚕豆和玉米幼苗根尖的染色体畸变诱导存在显著的浓度效应,即水浸提液浓度越高,受体的微核率和畸变率越高,相应的有丝分裂指数越低,水浸提液的诱导作用与浓度呈正相关关系,但不是简单的加和作用。(4)香丝草各器官水浸提液均具有较强的遗传毒性,但整体化感效应表现为叶＞幼果＞茎＞根,即叶片产生的化感作用最强。因此,香丝草分泌的化感物质可能通过对受体植物生长点的细胞有丝分裂和细胞形态产生影响,造成受体植物染色体的多种畸变和不可逆的遗传损伤,从而成功入侵新的栖息地。     

基质不同灭菌条件下空心莲子草浸提液对白三叶种子萌发和幼苗生长的影响

空心莲子草(Alternanthera philoxeroides Griseb)为广泛分布且亟待解决防除的重要外来恶性杂草, 其化感作用机制近年来逐渐引起人们的广泛关注。该研究通过添加空心莲子草地上和地下水浸提液和土壤灭菌处理来研究其对白三叶种子萌发和幼苗生长的影响, 以期深入理解空心莲子草的化感作用及其机理。结果表明, 土壤灭菌和空心莲子草浸提液处理及其交互作用对白三叶种子萌发率及其幼苗的芽长和根长均有显著或极显著影响。在基质未灭菌条件下,空心莲子草的地下浸提液表现为促进效应, 而地上浸提液表现为抑制效应; 在基质灭菌条件下, 空心莲子草地上和地下浸提液均表现为抑制效应, 但其抑制程度存在差异。相比地上浸提液, 地下浸提液的抑制程度更大且不同器官响应存在差异。相对于芽长, 根长受到的抑制作用更大。由此可见, 空心莲子草地下浸提液与地上浸提液的化感效应存在一定的差异, 在对其化感机理的研究中不仅要关注植株不同部位的作用效应差异, 同时要关注外界环境条件特别是土壤微生物的影响。     

白三叶入侵对草地早熟禾功能性状及草坪质量的影响

【目的】白三叶入侵会挤占草坪草的生存空间,严重威胁草坪的质量和功能。明晰白三叶（Trifolium repens）入侵对草坪植物草地早熟禾（Poa pratensis）功能性状及草坪质量的影响,可深入了解白三叶入侵机制,为禾本科草坪的建植养护提供理论依据。【方法】以白三叶入侵草地早熟禾草坪为研究对象,采用样地调查方法,考察不同白三叶入侵程度下（对照及轻度、中度、重度入侵）草地早熟禾功能性状及草坪质量的差异特征,并通过隶属函数法综合评价各入侵程度下草坪质量。【结果】（1）随白三叶入侵程度的增加,草地早熟禾各器官碳含量、叶片建成成本及碳氮比、碳磷比和氮磷比逐渐降低,而比叶面积、各器官氮和磷含量增大。（2）同一入侵程度下,草地早熟禾各器官碳、氮和磷含量均表现为叶大于根和茎,碳氮比和碳磷比表现为根和茎大于叶,而其氮磷比表现为茎和叶大于根。（3）随白三叶入侵程度的增加,草地早熟禾草坪密度、质地、绿度指数和均一性降低,而地上生物量和地下生物量增大。（4）隶属函数法综合评价结果显示,草坪质量以白三叶未入侵时最优,重度入侵时最差,且叶碳含量对草坪质量的影响最大。【结论】白三叶入侵改变了草地早熟禾功能性状,降低了入侵区草坪质量,严重影响了草坪景观和功能。     

喜旱莲子草组织水浸液对黑麦草种子和幼苗的化感效应

以喜旱莲子草(Alternanthera philoxeroides)地上和地下部组织为供体,黑麦草(Lolium perenne L.)为受体,运用室内培养皿生物测定方法研究了喜旱莲子草组织水浸液的化感作用.结果表明:喜旱莲子草组织水浸提液对黑麦草种子的萌发具有明显抑制作用,显著降低了其终萌发率,也明显抑制了黑麦草幼苗根和茎的生长;喜旱莲子草组织水浸提液处理使黑麦草幼苗叶片的电导率显著增加,但其叶绿素含量却明显降低;喜旱莲子草不同组织部位水浸提液的化感作用强弱不同,表现为地下部分水浸提液化感作用明显强于地上部分.     

外来杂草加拿大一枝黄花对入侵地植物的化感效应

采用人工气候箱培养试验,初步研究了入侵杂草加拿大一枝黄花对本地植物的化感作用.测定了根系和根状茎的不同浓度浸提液对白三叶发芽率和幼苗生长的影响;不同播种密度下根系1:60提取浓度对白三叶种子萌发和幼苗生长的影响;根状茎1:60提取浓度对白三叶、红三叶、天蓝苜蓿、黑麦草、北美车前、鸡眼草、苇状羊茅、胜红蓟、马齿苋、碱蓬和刺苋的种子萌发和幼苗生长的影响.结果表明,加拿大一枝黄花根系和根状茎的化感抑制作用均随浓度的升高而增强,且根状茎提取物的抑制效应高于根系提取物的效应;在1:60低浓度根系浸提液作用下,不同密度的白三叶幼苗萌发率和幼根、幼芽长度差异不显著;1:60低浓度根状茎提取物对11个物种的种子萌发均有显著抑制作用,但对不同物种的抑制程度有差异,对禾本科植物的抑制作用大于非禾本科和豆科;1:60低浓度根状茎提取物对10个物种的幼根影响与对萌发率的影响相似,但在对幼芽的影响上,仅对鸡眼草、刺苋和苇状羊茅起抑制作用,而对其他植物无显著抑制(黑麦草、北美车前、胜红蓟、马齿苋和刺苋)或起促进作用(白三叶、红三叶、天蓝苜蓿).     

Taxonomic status of the species of the green algal genusNeochloris

Komárek has recently reviewed the various species assigned to the green algal genusNeochloris Starr (Chlorococcales, Chlorococcaceae) and removed those with uninucleate vegetative cells to a new genus,Ettlia. Watanabe & Floyd, unaware ofKomárek's work, also reviewed the species ofNeochloris and distributed them among three genera—Neochloris, Chlorococcopsis gen. nov., andParietochloris gen. nov.—on the basis of details of the covering of the zoospore and the arrangement of the basal bodies of the flagellar apparatus. This paper reconciles these two treatments and makes additional recommendations at the ranks of genus, family, order, and class.     

Hectorella: A member of the betalain-suborderChenopodiineae of the orderCentrospermae

Roots ofHectorella caespitosa Hook. f. were induced to produce a red pigment which was shown to be a betalain and not an anthocyanin. These data indicate thatHectorella belongs to theChenopodiineae, the betalain suborder of theCentrospermae, and excludes alignment with the anthocyanin family theCaryophyllaceae.     

Succession in the southern part of the Canadian boreal forest

Forest succession following fire in a forest mosaic of northwestern Quebec has been studied in order to: (1) describe the successional pathways using communities of different ages and (2) evaluate convergence of successional pathways and possible effect of fire suppression on the establishment of steady-state communities. As a first step, ordination and classification techniques were used in order to remove changes in forest composition which are related to abiotic conditions. Then, ordinations based on tree diameter distributions were used to study shifts in species composition in relation to time since the last fire.Even under similar abiotic conditions, successional pathways are numerous. However, regardless of forest composition after fire, most stands show convergence toward dominance of Thuja occidentalis and Picea mariana on xeric sites and dominance of Abies balsamea and Thuja occidentalis on more mesic sites. Stable communities of >300 yr occur on xeric sites while on mesic sites directional succession still occurs after 224 yr. Nearly all species involved in succession are present in the first 50 yr following fire. Only Abies balsamea and Thuja occidentalis increase significantly in frequency during succession. Following initial establishment, successional processes can generally be explained by species longevity and shade tolerance. Early successional species may be abundant in the canopy for more than 200 yr while the rapid decrease of Picea glauca, a late successional species could be related to spruce budworm outbreaks. Considering the short fire rotation observed (about 150 yr), a steady-state forest is unlikely to occur under natural conditions, though it may be possible if fire is controlled.     

The purification of the three trimannosyl-N-acetylchitobiose pentasaccharides from the urine of swainsonine-intoxicated sheep

A simple method for the preparative resolution of three Man₃GlcNAc₂ isomers called Ia, Ib and II has been designed. It consists mainly of the use of concanavalin A-Sepharose which allowed the total purification of Man₃GlcNAc₂-Ia, and then of anion-exchange resin in borate buffer-gradient to separate the Ib and II isomers. The purity of each oligosaccharide was checked by two HPLC methods. The use of these oligosaccharides for different analytical and biosynthetic purposes is discussed, and the unexpected resistance of one of the Man₃GlcNAc₂ alditols to the action of endo--N-acetylglucosaminidase H is noted.     

Evaluation of the Pro-Lab ID ring system for the identification of medically important yeasts

We evaluated 151 coded isolates of medically important yeast species belonging to the genera Candida, Cryptococcus, Geotrichum, Rhodoturula, Saccharomyces and Torulopsis using the newly developed rapid Pro-Lab Identification Ring, PL 960 system (PLID-Ring). All isolates were concurrently identified by the API 20C and conventional procedures comprising macro- and micromorphology, assimilation and fermentation of various carbon and nitrogen compounds. The PLID-Ring system identified isolates of Candida albicans, C. kefyr, C. krusei, C. lusitaniae, C. parapsilosis, Rhodotorula rubra, and Torulopsis glabrata with 100% accuracy in 24 h. This system identified C guilliermondii and S. cerevisiae isolates with an accuracy of 90% and 86%, respectively, while those belonging to Cr. neoformans, T. candida (= C. famata), C. rugosa and C. tropicalis were identified with 38.4%, 50%, 12.5% and 50% accuracy, respectively. Three isolates of Cr. laurentii were not identified by the PLID-Ring system. The overall accuracy of the PLID-Ring system was 81.45% (123 of 151 isolates). However, the system does not include species such as Cr. laurentii in its data base. When these three Cr. laurentii isolates were excluded from the evaluation, the accuracy of the PLID-Ring system increased from 81.45% to 83.1%.     

Analysis of the genes of the OEE1 and OEE3 proteins of the photosystem II complex from Chlamydomonas reinhardtii

The sequences of the nuclear genes of the 33 kDa (OEE1) and the 16 kDa (OEE3) polypeptides of the oxygen evolving complex of Chlamydomonas reinhardtii have been established. Comparison between the OEE1 protein sequences of C. reinhardtii and higher plants and cyanobacteria reveals 67 and 47% homology. In contrast, C. reinhardtii and higher plants have only 28% overall homology for OEE3 which is mostly limited to the central portion of the protein. The transit peptides of the C. reinhardtii proteins consist of 52 (OEE1) and, most likely, 51 (OEE1) amino acids. They have a basic amino terminal region and, at least in the case of OEE1, a hydrophobic segment at their carboxy terminal end typical of thylakoid lumen proteins. Comparison of the genomic and cDNA clones indicates that the OEE1 and OEE3 genes contain five and four introns, respectively, some of which are located within the coding sequences of the transit peptides.     

Progress on the genetics of the N2-fixing actinorhizal symbiont Frankia

The actinomycete Frankia is of fundamental and ecological interests for several reasons including its wide distribution, its ability to fix nitrogen, differentiate into sporangium and vesicle (specialized cell for nitrogen-fixation), and to nodulate plants from about 24 genera. Here, we present a review on the genetics performed so far on Frankia. At the end of July 2001, 293 kbp of Frankia DNA sequences were found in the databases. Thirty five percent of these sequences corresponded to full gene or gene cluster sequences. These genes could be divided according to their role into 6 key activities: gene translation (rrnA and tRNA ^pro gene), proteolysis (pcr genes), assimilation of ammonium (glnA and glnII), protection against superoxide ions (sodF), nitrogen fixation (nif cluster), and plasmid replication. We present a review of these genetic islands; their function, expression, localization and particular properties are discussed. A comparative analysis of Frankia nif genes from various strains and species is presented. An improved nomenclature for some of these genes is suggested to avoid conflicts. Frankia plasmids DNA sequences are also presented. The novel trends in Frankia genetics are described.     

The history of the genusHomo

The genusHomo was established by Carolus Linnaeus in 1758. During the course of the past 150 years, the addition of fossil species to the genusHomo has resulted in a genus that, according to the taxonomic interpretation, could span as much time as 2.5 Myr, and include as many as ten species. This paper reviews the fossil evidence for each of the species involved, and sets out the case for their inclusion inHomo. It suggests that while the case for the inclusion of some species in the genus (e.g.Homo erectus) is well-supported, in the case of two of the species,Homo habilis andHomo rudolfensis, the case for their inclusion is much weaker. Neither the cladistic evidence, nor evidence about adaptation suggest a particularly close relationship with laterHomo.     

Comparative analysis of the Kekkon molecules,related members of the LIG superfamily

Leucine-rich repeats (LRRs) and immunoglobulin (Ig) domains represent two of the most abundant sequence elements in metazoan proteomes. Despite this prevalence, comparatively few molecules containing both LRR and Ig (LIG) modules exist, and fewer still have been functionally defined. One LIG whose function has been investigated is the Drosophila protein Kekkon1 (Kek1). In vivo studies have demonstrated a role for Kek1 in Epidermal Growth Factor Receptor (EGFR) signaling and have suggested a role in neuronal pathfinding. Kek1 is the founding member of the Kek family, a group of six Drosophila transmembrane proteins that contain seven LRRs and a single Ig in their extracellular domains. While this arrangement of domains predicts a possible role as cell adhesion molecules (CAMs), to date little is known about the function or evolutionary relationship of these additional Kek molecules. Here we report that orthologs of Kek1, Kek2, Kek5, and Kek6 exist in the mosquito, Anopheles gambiae, and the honeybee, Apis mellifera, indicating that this family has been conserved for ~300 million years of evolutionary time. Comparative sequence analyses reveal remarkable identity among these orthologs, primarily in their extracellular regions. In contrast, the intracellular regions are more divergent, exhibiting only small pockets of conservation. In addition, we provide support for the general notion that these molecules may share common functions as CAMs, by demonstrating that Kek family members can form homotypic and heterotypic complexes.Edited by D. TautzChristina M. MacLaren, Timothy A. Evans and Diego Alvarado contributed equally to this work