Digestive function of lysozyme in synanthropic acaridid mites enables utilization of bacteria as a food source

The activity of lysozyme, the enzyme that hydrolyzes peptidoglycan in G⁺ bacterial cell walls, was detected in whole mite extracts (WME) and in spent growth medium extracts (SGME) of 14 species of synanthropic mites (Acari: Acaridida). The adaptation of lysozyme for digestive activity and bacteriophagy was based on: (i) high lysozyme activity in SGME, and (ii) the correlation of maximum lysozyme activity at acidic pH values, corresponding to pH in the ventriculus and caeca. We show that the digestion of fluorescein-labeled Micrococcus lysodeikticus cells began in ventriculus and continued during the passage of a food bolus through the gut. The fluorescein was absorbed by midgut cells and penetrated to parenchymal tissues. Eight species showed a higher rate of population growth on a M. lysodeikticus diet than on a control diet. The lysozyme activity in SGME was positively correlated to the standardized rate (r _s) of population growth, although no correlation was found between r _s and lysozyme activity in WME. The lysozyme activity in WME was negatively correlated to that in SGME. The highest activity of digestive lysozyme was found in Lepidoglyphus destructor, Chortoglyphus arcuatus and Dermatophagoides farinae. All of these findings indicate that lysozyme in acaridid mites possesses both defensive and digestive functions. The enzymatic properties of mite lysozyme are similar to those of the lysozymes present in the ruminant stomach and in the insect midgut.     

On the atrophy of the internal carotid artery in capybara

Capybara might be a useful model for studying changes in cerebral circulation as the natural atrophy of the internal carotid artery (ICA) occurs in this animal at maturation. In this study, confocal and electron microscopy combined with immunohistochemical techniques were applied in order to reveal the changes in morphology and innervation to the proximal part of ICA in young (6-month-old) and mature (12-month-old) capybaras. Some features of the basilar artery (BA) were also revealed. The ICA of young animals degenerated to a ligamentous cord in mature animals. Immunolabelling positive for pan-neuronal marker protein gene product 9.5 but negative for tyrosine hydroxylase was observed in the proximal part of ICA at both ages examined. Axon varicosities positive for synaptophysin were present in the adventitia of ICA of young animals but were absent in the ligamentous cord of mature animals. In the ICA of young animals, adventitial connective tissue invaded the media suggesting that the process of regression of this artery began within the first 6 months of life. An increase in size of the BA was found in mature animals indicating increased blood flow in the vertebro-basilar system, possibly making capybara susceptible to cerebrovascular pathology (e.g. stroke). Capybara may therefore provide a natural model for studying adaptive responses to ICA regression/occlusion.The financial support of the Graduate Fund, UCL, London, UK (C. Steele) and the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) Brazil (200516/01-9; A.A.C.M. Ribeiro) is gratefully acknowledged.     

The alkaloidal responses of wild tobacco to real and simulated herbivory

Summary I compared the induced alkaloidal response in undamaged leaves of plants subjected to herbivory by the larvae of Manduca sexta and to different simulations of this herbivory; all herbivory treatments removed similar amounts of leaf mass. Although larval feeding induced a significant increase (2.2x) in alkaloid concentrations compared to undamaged plants, the alkaloid responses to larval feeding were significantly lower than the responses to an herbivory simulation (4x controls) which involved removing the same amount of leaf area from the same positions on the leaf, over a similar time period. Moreover, another herbivory simulation, identical in amount of leaf mass removed and duration of damage to the larval feeding, but without regard to spatial array of leaf damage, resulted in an alkaloidal response (5.5x controls) higher still than the previous herbivory simulation. In a second experiment the importance of leaf vein damage on the induced alkaloidal response was examined. Here, leaf removal that involved cutting leaf tissues from between secondary veins before removing the midrib, resulted in alkaloidal responses that were significantly lower (1.7x controls) than responses from leaf removal that involved cutting both veins and midribs along with the intervein tissues (2.6x controls). Vein damage alone did not produce a significant response. These results indicate that herbivory is difficult to simulate: that how a leaf is damaged can be as important as the magnitude of leaf damage in determining a plant's response to damage.     

Impact of epidermal leaf mining by the aspen leaf miner (Phyllocnistis populiella) on the growth, physiology, and leaf longevity of quaking aspen

The aspen leaf miner, Phyllocnistis populiella, feeds on the contents of epidermal cells on both top (adaxial) and bottom (abaxial) surfaces of quaking aspen leaves, leaving the photosynthetic tissue of the mesophyll intact. This type of feeding is taxonomically restricted to a small subset of leaf mining insects but can cause widespread plant damage during outbreaks. We studied the effect of epidermal mining on aspen growth and physiology during an outbreak of P. populiella in the boreal forest of interior Alaska. Experimental reduction of leaf miner density across two sites and 3 years significantly increased annual aspen growth rates relative to naturally mined controls. Leaf mining damage was negatively related to leaf longevity. Leaves with heavy mining damage abscised 4 weeks earlier, on average, than leaves with minimal mining damage. Mining damage to the top and bottom surfaces of leaves had different effects on physiology. Mining on the top surface of the leaf had no significant effect on photosynthesis or conductance and was unrelated to leaf stable C isotope ratio (delta(13)C). Mining damage to the bottom leaf surface, where stomata are located, had significant negative effects on net photosynthesis and water vapor conductance. Percent bottom mining was positively related to leaf delta(13)C. Taken together, the data suggest that the primary mechanism for the reduction of photosynthesis by epidermal leaf mining by P. populiella is the failure of stomata to open normally on bottom-mined leaves.     

Comparative physiology of burned and unburned Rhus laurina after chaparral wildfire

Summary Laurel Sumac (Rhus laurina) is a dominant member of the coastal chaparral community of southern California that survives periodic burning by wildfires by resprouting from a lignotuber (root crown). We investigated the physiological basis for resprouting by comparing shoot elongation, leaf nitrogen content, tissue water status, leaf conductance to water vapor diffusion, and photosynthetic rates of post-fire R. laurina to those of adjacent unburned shrubs. Resprouts had higher rates of shoot elongation, leaf conductance, and photosynthesis than mature, unburned shrubs. Leaf nitrogen contents were elevated in burned shrubs even though their leaves developed interveinal chlorosis. A comparison of soil water potential to predawn water potential indicated that roots of R. laurina remain active below 2 m during the first summer drought after wildfire. Our results support the hypothesis that lignotubers not only contain dormant buds that develop into aerial shoots after wildfire but they also supply nutrient resources that enhance shoot elongation. Because R. laurina is relatively sensitive to drought, yet very successful in its rapid recovery after fire, maintaining an active root system after shoot removal may be the primary function of the massive lignotuber formed by this species.     

野生杜鹃杂交亲和性及适宜的评价指标

以映山红和马银花为母本,映山红亚属、羊踯躅亚属、杜鹃亚属、常绿杜鹃亚属以及马银花亚属的5个亚属16个中国野生杜鹃种为父本进行杂交授粉,统计子房膨大率、坐果率和种子萌发率,分析杜鹃属植物远缘杂交的亲和性,探讨其杂交亲和性适宜的评价指标。结果表明:映山红作为母本,与同亚属的杜鹃杂交亲和性较好,与其它亚属的杜鹃种的杂交亲和性存在显著的亚属间和种间差异;而马银花作为母本,与同亚属的西施花进行杂交,未获得杂交果实和种子,但与杜鹃其它亚属种的杂交,部分杂交组合显示出较好的杂交亲和性。这一结果表明,映山红作为母本,与马银花相比,有着较好的杂交亲和性,并且杜鹃属植物的杂交亲和性与目前杜鹃分类体系中的亲缘关系并没有直接关系。进一步的数据分析表明,子房膨大率与坐果率、坐果率与蒴果平均种子数之间呈显著正相关,但子房膨大率与果实内种子数无直接相关性;花粉活力(大于15%)、父母本花柱长度比(在0.50~2.12范围内)与子房膨大率等亲和性指标无显著相关性。     

Phylogenetic position and physiology of Cerinosterus cyanescens

Partial 25S rRNA sequencing of Cerinosterus cyanescens showed it to be a close relative of Microstroma juglandis, a member of the basidiomycetous order Microstromatales. It is unrelated to the generic type species, C. luteoalba, which is a member of the order Dacrymycetales. The clinical occurrence of C. cyanescens is possibly explained by its thermotolerance and lipolytic activity. The species' nutritional profile is established. Growth on n-hexadecane is rapid; it grows well on typical plant constituents like gallic, tannic, vanillic, quinic and p-coumaric acids, but not on 3-hydroxybenzoic acid, phenol and hydroquinone. The failure to assimilate D-galactose, L-sorbose and ethylamine, the presence of urease and sensitivity to cycloheximide are diagnostic for the species.     

Stimulation of soil nitrification and denitrification by grazing in grasslands: do changes in plant species composition matter?

Stimulation of nitrification and denitrification by long term (from years to decades) grazing has commonly been reported in different grassland ecosystems. However, grazing generally induces important changes in plant species composition, and whether changes in nitrification and denitrification are primarily due to changes in vegetation composition has never been tested. We compared soil nitrification- and denitrification-enzyme activities (NEA and DEA, respectively) between semi-natural grassland sites experiencing intensive (IG) and light (LG) grazing/mowing regimes for 13 years. Mean NEA and DEA (i.e. observed from random soil sampling) were higher in IG than LG sites. The NEA/DEA ratio was higher in IG than LG sites, indicating a higher stimulation of nitrification. Marked changes in plant species composition were observed in response to the grazing/mowing regime. In particular, the specific phytomass volume of Elymus repens was lower in IG than LG sites, whereas the specific volume of Lolium perenne was higher in IG than LG sites. In contrast, the specific volume of Holcus lanatus, Poa trivialis and Arrhenatherum elatius were not significantly different between treatments. Soils sampled beneath grass tussocks of the last three species exhibited higher DEA, NEA and NEA/DEA ratio in IG than LG sites. For a given grazing regime, plant species did not affect significantly soil DEA, NEA and NEA/DEA ratio. The modification of plant species composition is thus not the primary factor driving changes in nitrification and denitrification in semi-natural grassland ecosystems experiencing long term intensive grazing. Factors such as trampling, N returned in animal excreta, and/or modification of N uptake and C exudation by frequently defoliated plants could be responsible for the enhanced microbial activities.     

野生荞麦细柄野荞麦的繁殖生物学特性研究

该研究通过野外观察和人工控制实验相结合的方法,从开花动态、花部基本特征、繁育系统、传粉生物学及种子性状等方面对荞麦属(Fagopyrum Mill.)植物细柄野荞麦(Fagopyrum gracilipes)的繁殖生物学特性进行了探究,并分析了各性状对其繁殖的贡献。结果表明:在贵州威宁,细柄野荞麦的花果期常为每年的6—10月,单花序和单花的花期分别为13～21 d和1～3 d。花较小,直径为(3.99±0.12) mm,花柱和花药高分别为1.30和1.65 mm,花直径与花被片长和花被片宽呈显著正相关,花柱高与花药高呈极显著正相关。细柄野荞麦花粉胚珠比为371±16.40,杂交指数为2,套袋实验显示其自交、异交亲和,表明其繁育系统为兼性自交,部分异交亲和。细柄野荞麦的访花昆虫较少,主要为膜翅目(Hymenoptera)、双翅目(Diptera)和鞘翅目(Coleoptera) 7个科的9种昆虫,食蚜蝇科(Syrphidae)昆虫是其主要传粉昆虫。细柄野荞麦果实存在有翅和无翅两种类型,有利于其适应不同的传播方式,种子较小,千粒重为(1.05±0.04) g,萌发率较低,播种后30 d的累积萌发率为(19.60±2.14)%,但萌发整齐,主要集中在前5 d。综上所述,细柄野荞麦灵活的繁育系统为其产生大量种子提供了保障,多样的果实传播方式和整齐的种子萌发特性为其占据更广阔的生境成为群落优势种创造了基础。     

Comparative physiology of nitrogenase activity and vesicle development for Frankia strains CpI1, ACN1 ag,EAN1pec and EUN1f

The relationship between nitrogen fixation and development of a specialized cell structure, called the vesicle, was studied using four Frankia isolates. Nitrogenase activity was repressed in all four strains during growth with ammonia. Strain CpI1 formed no vesicles during NH₄ growth. Strains ACN1 ^ag , EAN1_pec and EUN1_f produced low numbers of vesicles in the presence of ammonia. Following transfer to nitrogen-free media, a parallel increase in nitrogenase activity and vesicle numbers occurred with all four isolates. Appearance of nitrogenase activity was more rapid in those strains that possessed some vesicles at the time of shift to N₂ as a nitrogen source. The ratio of vesicle numbers to level of nitrogenase activity varied widely among the four strains and in response to different growth conditions and culture age of the individual strains. Optimum conditions of temperature, carbon and energy source, nitrogen source and availability of iron and molybdenum were different for each of the four strains. Those conditions that significantly reduced nitrogenase activity were always associated with decreased numbers of vesicles.     

Morphology,physiology and infectivity of twoFrankia isolates An 1 and An 2 from root nodules ofAlnus nitida

Summary Two different strains, An 1 and An 2, were obtained from root nodules ofAlnus nitida Endl., collected from one locality in the area of its natural habitat near Bahrin, District Swat, Pakistan. The light and electron microscopy of the isolates revealed the occurrence of septate and branched hyphae bearing sporangia and vesicles. The strains differed in their growth requirements, nitrogen-fixing ability and production of extracellular pigments, thus indicating the existence of more than oneFrankia strain in the same locality. In the absence of combined nitrogen in the medium strain An 1 formed vesicles and fixed N₂ (up to 200 nmol C₂H₄. mg protein^–1.h^–1), while strain An 2 under the experimental conditions formed only few vesicles and fixed N₂ at a very low rate (ca 10 nmol C₂H₄. mg protein^–1 .h^–1). The nitrogenase activity of strain An 1 was strongly affected by the O₂ concentration.Frankia An 1 and An 2 were infective and effective onA. nitida andA. glutinosa but not onDatisca cannabina andElaeagnus umbellata. Both An 1 and An 2 strains were more infective and effective onA. glutinosa thanFrankia strains AvcIl and CpI1.     

Galerucella nymphaeae (Col., Chrysomelidae) grazing increases Nuphar leaf production and affects carbon and nitrogen dynamics in ponds

Summary The grazing effects of the waterlily beetle Galerucella nymphaeae on Nuphar lutea stands were studied in three ponds in Central Finland. Production of floating leaves of N. lutea and growth in the G. nymphaeae population were investigated in the ponds and bioenergetics of the beetle larvae in the laboratory. Combination of field and laboratory data enabled estimation of the effect of the beetle on the production of floating leaves of N. lutea and the consequences of grazing for the input of detritus from Nuphar into the ponds. Adults and larvae of G. nymphaeae consumed 3.0–6.1% of the net annual floating leaf production during the growing period. In addition to consumption losses, feeding accelerated the degradation rate of the leaves. This was associated with an increased flow of detrital material of Nuphar origin, and also with increased production of floating leaves in the ponds. These increments were estimated to be up to 3 times greater in the presence of grazing than without it. Grazing by G. nymphaeae releases substantial amounts of carbon and nitrogen bound in Nuphar, particularly in ponds with a dense Nuphar vegetation. It is hypothesized that feeding by this beetle may markedly affect the structure and functioning of such small aquatic systems.     

枇杷属内栽培种和部分野生种ITS序列分析

对不同栽培区的25种普通枇杷品种以及7种枇杷属野生种的ITS序列进行扩增并测序,采用邻接法和最大简约法进行系统发育树的构建并对枇杷属内不同种间的遗传关系进行了分析。结果表明:枇杷属植物ITS序列ITS1+5.8S rDNA+ITS2总长度为592 bp或594 bp,长度变化发生在ITS2。所有样本的ITS1和5.8S rDNA长度一样,都是223 bp和168 bp;而ITS2为201 bp或203 bp。5种枇杷属野生种的ITS序列长度为594 bp,包括栎叶枇杷、大渡河枇杷、南亚枇杷、南亚枇杷窄叶变种和大瑶山枇杷;其余2种枇杷属野生种(麻栗坡枇杷、小叶枇杷)和普通枇杷栽培种的ITS序列长度都为592 bp。所有样本ITS序列的GC含量为64.2%~64.5%,其中ITS1为64.1%~65.5%,ITS2为68.1%~72.6%。对所有样本的ITS序列比对产生44个可变位点,其中38个为简约信息位点,其中11个位于ITS1,5个位于5.8S rDNA,22个位于ITS2。最大的种间序列差异为7.7%,最小的种间差异发生在麻栗坡枇杷和小叶枇杷之间,仅为0.2%。普通枇杷种内的ITS序列差异很低,25种普通枇杷栽培种之间的序列差异为0~1.5%。所研究的枇杷属植物可分为3个分支。分支Ⅰ包括所有普通枇杷品种,分支Ⅱ包含5种野生枇杷种,包括栎叶枇杷、大渡河枇杷、南亚枇杷、南亚枇杷窄叶变种和大瑶山枇杷;分支Ⅲ由2个野生枇杷种(麻栗坡枇杷、小叶枇杷)组成。该研究结果表明ITS序列对枇杷种间鉴定和系统发育分析具有一定意义,但对普通枇杷栽培种间的鉴定作用不大。     

Nutritional physiology of type isolates of currently accepted species ofExophiala andPhaeococcomyces

Nutritional physiological and tolerance tests were performed for all type strains of species currently classified in the black yeast generaExophiala andPhaeococcomyces, including some additional type strains of taxa recently reidentified asExophiala species. Most describedExophiala species can be distinguished by physiological characters.Exophiala jeanselmei with its varieties, andE. castellanii should all be retained as separate taxa. The pairs of strainsMycotorula schawii/Exophiala dermatitidis, Hormodendrum negronii/Exophiala jeanselmei var.lecaniicorni andSporotrichum gougerotii/Torula bergeri were found to be conspecific. Phenetic analyses of physiological data support the identity ofPhaeococcomyces exophialae as a yeast-like synanamorph ofExophiala spinifera. The taxonomic positions of the generaNadsoniella, Phaeoannellomyces andWangiella are discussed. The generaExophiala andPhaeococcomyces are unrelated.     

Conidiogenesis,nutritional physiology and taxonomy ofAureobasidium andHormonema

Diagnostic criteria for the distinction of the slightly osmophilic species,Aureobasidium pullulans, and the opportunistic pathogen on conifers,Hormonema dematioides, are provided. Reliable identification requires a combination of characters of conidiogenesis, expansion growth and assimilative abilities. Relationships with species ofKabatiella, and with the teleomorph generaPringsheimia, Dothidea andDothiora, all havingHormonema-like cultural states, are discussed. An identification key is provided.     

碳酸氢盐处理下桑树和构树的生长、光合和抗逆性差异

为探究喀斯特生境中,在碳酸氢盐的胁迫下HCO^-₃对植株生长及生理特性的影响,该文以构树和桑树幼苗为研究对象,对不同浓度NaHCO₃溶液(0、15、30 mmol·L^-1)处理下植株的生长情况、光合能力、抗氧化酶活性、渗透调节物质含量和细胞膜系统损伤情况进行研究。结果表明:(1)在HCO^-₃处理下,构树和桑树的生长和光合能力均受到抑制,叶片细胞内均发生显著的抗氧化和抗渗透胁迫生理响应。(2)HCO^-₃对构树和桑树生长的抑制作用与其浓度有关,并有显著差异性(P<0.05)。(3)30 mmol·L^-1 HCO^-₃处理对植株生长、光合、抗氧化酶系统和渗透调节系统的抑制作用以及植物细胞的损伤情况要显著强于15 mmol·L^-1 HCO^-₃处理的效果。(4)同等浓度的HCO^-₃处理下,构树的生长、光合能力、抗氧化酶活性、渗透调节物质含量显著高于桑树,其叶片细胞损伤情况显著低于桑树。综上结果均表明,构树对碳酸氢盐胁迫的耐受能力要优于桑树。该研究为阐明桑科植物对喀斯特环境适应机制提供科学支撑。     

野生茯苓鉴定及其木质纤维素降解酶系研究

为揭示茯苓木质纤维素降解酶系及培养方式对其主要酶系的影响,该研究通过对野生茯苓菌株进行培养特性的显微观察,利用3对引物PCR扩增进行系统发育学的鉴定,经定性培养筛选出优势菌株YX1,采用酶标仪测定不同条件下茯苓纤维素酶、半纤维素酶和木质素降解酶的活力大小。结果表明：(1)茯苓有菌丝体、子实体和菌核3种形态特征。(2)PCR分别获得rDNA-ITS序列1 652 bp、核糖体大亚基序列660 bp和翻译延伸因子序列545 bp,提交至NCBI,登录号分别为ON129554、ON129553和ON155840。(3)纤维素酶和半纤维素酶在有松木屑和无松木屑条件下,外切β-葡聚糖酶(CBH)、内切β-葡聚糖酶(EG)、β-葡萄糖苷酶(BGL)最高分泌量分别为16～17 U·mL^-1、32～35 U·mL^-1、36～37 U·mL^-1;木聚糖酶、甘露聚糖酶和α-葡萄糖苷酶最高分泌量分别为28～38 U·mL^-1、280～342 U·mL^-1、9～11 U·mL^-1...     

Nitrogen-15 partitioning within a three generation tiller sequence of the bunchgrass Schizachyrium scoparium: response to selective defoliation

Summary Nitrogen partitioning among three generations of tillers within the bunchgrass Schizachyrium scoparium var. frequens was investigated in a controlled environment as a potential mechanism of herbivory tolerance. Nitrogen-15 was transported from the labelled primary tiller generation to both shoots and roots of nondefoliated secondary and tertiary tiller generations within 24 h. Partial defoliation increased shoot nitrogen concentration of secondary and tertiary generation tillers by 110 and 120%, respectively, 24 h following defoliation. Shoot nitrogen concentration was preferentially increased by partial defoliation of tertiary generation tillers throughout the 120 h experimental period, but diminished to concentrations comparable to nondefoliated tillers within shoots of the secondary generation at 72 h. In contrast to nitrogen concentration, the total amount of nitrogen imported by secondary and tertiary generation tillers decreased 62 and 73%, respectively, 24 h following partial defoliation and did not attain values comparable to respective nondefoliated tillers. Consequently, preferential nitrogen concentration occurred in response to partial tiller defoliation without an increase in total nitrogen import based on the reduction in the total nitrogen requirement per tiller generation associated with defoliation. Estimates of both the total amount of nitrogen import and nitrogen concentration are necessary to accurately interpret the dynamics of intertiller nitrogen allocation.