Neuropepride Regulators of Insect Corpora Allata

SYNOPSIS. Neuropeptides of the insect brain that regulate juvenilehormone synthesis by the corpora allata include allatotropins,stimulatory modulators, and allatostatins, inhibitory modulators.A radiochemical assay for juvenile hormone synthesis by corporaallata in vitro was utilized in the high pressure liquid chromatographicisolation of brain neuropeptides leading to the determinationof their primary structure. Identified are an allatotropin andan allatostatin from a Lepidopteran, Manduca sexta, and a familyof five allatostatins from a Dictyopteran, Diploptera punctata.These neuropeptides are all unique, effective at low concentration(10^–10 to 10^–8 M), act quickly (within hrs) andappear to be effective only within the same order of insectsas that from which the peptides were isolated. The physiologicalstate of the corpora allata conditions the effectiveness ofthe allatostatins of D. punctata. These neuropeptide regulatorsof corpora allatal function may have multiple regulatory roles.This is indicated for D. punctata allatostatin I by specificreceptors in brain and fat body as well as in corpora allatalmembrane preparations, and also by immunocytochemical localizationof allatostatin I in medial nerve cells that terminate withinthe brain as well as in the lateral neurosecretory cells thatterminate on corpus allatum cells.     

Lack of humoral control in calling and pheromone release by brain,corpora cardiaca,corpora allata and ovaries of the female gypsy moth, Lymantria dispar (L.)

Investigations into the physiological regulation of calling behaviour and pheromone release by the adult female gypsy moth, Lymantria dispar, showed that the brain, corpora cardiaca, corpora allata and ovaries play no significant endocrine role for either calling behaviour or pheromone release. Removal of corpora allata, corpora cardiaca-corpora allata complex and ovaries from last-instar larvae had no effect on calling behaviour nor on the pheromone release in the resulting moths. Severing the suboesophageal connectives had no effect on calling, but effectively eliminated pheromone release. Since severing nerves should not remove humoral output from the brain, the regulation on pheromone release appears neural.     

Increase in final stages of follicular atresia and premature decay of corpora lutea in Insl3-deficient mice

The insulin-like factor 3 (Insl3), a member of the insulin-like hormone family, is exclusively synthesized in gonads. Our recent analysis of Insl3-deficient mice revealed the regulating role of the Insl3 factor on the gubernaculum development during the transabdominal descent of the testis. Here we define the role of the Insl3 factor by histometric analysis of wild-type and Insl3(-/-) ovaries. Ovaries from 40-day-old- and 6-month-old Insl3(-/-) mice as well as from wild-type littermates were serially sectioned. Sections were stained with periodic acid Schiff reaction (PAS) for counting the number of zonae pellucidae which indicated the final stages of follicular atresia. Corpora lutea were also determined. Some sections were processed using either a modified TUNEL method for in situ detection of apoptosis or a lectin labelling technique with Griffonia simplicifolia I agglutinin (GS I) for endothelial cell occurrence. The number of zonae pellucidae was higher in Insl3-deficient ovaries of both ages than in ovaries of wild-type sisters (P < 0.05 for 40-day-old ovaries; P < 0.01 for 6-month-old ovaries). Additionally, the wild-type mice of both ages possessed threefold more corpora lutea than their Insl3 littermates (P < 0.01 for 40-day-old; P < 0.001 for 6-month-old). In general, wild-type corpora lutea looked healthy, showed GS I-positive endothelial cells and no apoptotic cells. Corpora lutea from mutants were rich in regressing GS I luteal cells, and apoptotic cells appeared. We conclude: Follicular atresia and luteolysis are accelerated in ovaries of Insl3-deficient mice probably because of increased apoptosis. The Insl3 function thus appears to rescue endocrine cells from the apoptotic pathway.     

Historical Zoogeography of the Eusuchian Crocodilians: A Physiological Perspective

The historical zoogeography of eusuchian crocodilians has rarelybeen reviewed in any detail and yet is of increasing interestto students of crocodilian biology as large amounts of comparativeinformation on a wide range of species come to hand. Previousinterpretations of crocodilian zoogeography have been basedon one or another of two assumptions–that the major continentalland masses have remained more or less fixed in position, andthat the eusuchians have had only very limited powers of dispersalacross marine barriers. Both of these assumptions are inappropriatein light of our present knowledge of continental drift and crocodilianphysiology. In this paper we attempt a reinterpretation of eusuchian zoogeographybased on new information on their systematic relationships,physiological capacity for marine dispersal, and fossil history.We postulate that anatomical and physiological adaptations toa marine existence have played an important role in eusuchianhistory. We propose that Gavialis and Tomistoma, now restrictedto fresh waters, may have been derived secondarily from ancestorsadapted to salt water. In the case of Tomistoma, similaritiesin lingual gland and buccal cavity anatomy to the true crocodiles(Crocodylus and Osteolaemus) suggest that marine adaptationspredated the divergence of tomistomine and crocodyline stocks.The buccal morphology of Gavialis suggests it also has a marineancestry. Its systematic affinities are uncertain, lying perhapswith Tomistoma or, on other interpretations, with the Mesosuchia.In both cases, the fossil record is not inconsistent with thispossibility. Palaeontological information now available is inadequate toreconstruct the evolutionary history of the Eusuchia in detail.However, saltwater adapted eusuchians are more common in thefossil record than is widely recognized and the likelihood ofdispersal across marine "barriers" by non-alligatorid crocodilianscannot be ignored.     

Genetic and Hormonal Regulation of Vitellogenesis in Drosophila

In Drosophila the female-specific yolk protein, or vitellogenin,is synthesized in the fat body. In D. melanogaster, vitellogenin,is first detected in the female hemolymph at the time of adulteclosion and in the ovaries 20 hours later, suggesting differentregulatory mechanisms for the processes of synthesis and uptake.Transplantations of pupal or immature adult ovaries into D.melanogaster adult males induce vitellogenin synthesis, implicatingan ovarian agent in the control of synthesis. Larval ovariesfail to stimulate synthesis. Female-sterile mutants with rudimentaryor previtellogenic ovaries synthesize and accumulate large quantitiesof vitellogenin in the hemolymph, but not in the ovaries. Transplantationof these rudimentary ovaries into males induces vitellogeninsynthesis, suggesting that the ovarian inducing agent does notoriginate from the germ cells. Treatment of the homozygous female-sterilemutants with juvenile hormone stimulates the uptake of vitellogeninby the ovary in some strains. This shows that juvenile hormoneplays a role in vitellogenin uptake. The potential importanceof Drosophila vitellogenesis for studies of gene regulationis discussed.     

Do transparent exopolymer particles (TEP) inhibit grazing by the euphausiid Euphausia pacifica?

The hypothesis that ubiquitous, sticky transparent exopolymerparticles (TEP) formed from phytoplankton exudates will adhereto and coat the feeding structures of marine zooplankton grazers,and thus depress feeding on phytoplankton, was tested usingthe euphausiid, Euphausia pacifica, as a model organism. Duringtwo feeding experiments, E.pacifica were offered cells of thediatom Thalassiosira weissflogii, TEP, or both TEP and T.weissflogiicells. Ingestion rates on cells were lower in the presence ofTEP. However, contrary to the hypothesis, grazing on cells wasnot inhibited by TEP. Rather, TEP-clusters, aggregates whichformed from TEP and nano-sized particles normally too smallfor the filtering apparatus of E.pacifica to retain, servedas an alternative food source for E.pacifica, reducing theiringestion of cells. These clusters were very similar in formto the TEP actually available to marine grazers in nature. TEP-clusterswere similar to cells in size and food quality, and were grazedat similar rates. When feeding on TEP-clusters, euphausiidsshort circuit the food web by feeding on nano- and picoplanktondirectly, bypassing the microbial loop. Thus, the presence ofTEP appears to enhance, rather than depress, macrozooplanktongrazing.     

Mitochondrial genomes of Galathealinum, Helobdella, and Platynereis: sequence and gene arrangement comparisons indicate that Pogonophora is not a phylum and Annelida and Arthropoda are not sister taxa

We report a contiguous region of more than half (>7,500 nt)of the mitochondrial genomes for Platynereis dumerii (Annelida:Polychaeta), Helobdella robusta (Annelida: Hirudinida), andGalathealinum brachiosum (Pogonophora: Perviata). The relativearrangements of all 22 genes identified for Helobdella and Galathealinumare identical to one another and to their arrangements in themtDNA of the previously studied oligochaete annelid Lumbricus.In contrast, Platynereis differs from these taxa in the positionsof several tRNA genes and in having two additional tRNA genes(trnC and trnM) and a large noncoding sequence in this region.Comparisons of relative gene arrangements and of the nucleotideand inferred amino acid sequences among these and other publishedtaxa provide strong support for an annelid-mollusk clade thatexcludes arthropods, and for the inclusion of pogonophoranswithin Annelida, rather than giving them separate phylum status.Gene arrangement comparisons include the first use of a recentlydescribed method on previously unpublished data. Although avariety of alternative initiation codons are typically usedby mitochondrial protein-encoding genes, ATG appears to be theinitiator for all but one reported here. The large noncodingregion (1,091 nt) identified in Platynereis has no significantsequence similarity to the noncoding region of Lumbricus, althougheach contains runs of TA dinucleotides and of homopolymers,which could potentially serve as signaling elements. There isstrong bias for synonymous codon usage in Helobdella and especiallyin Galathealinum. In this latter taxon, 5 codons are completelyunused, 13 are used three or fewer times, and G appears at thirdcodon positions in only 26 of the 2,236 codons. Nucleotide compositionbias appears to influence amino acid composition of the proteins.     

Factors Affecting Shedding of Flowers in Soybean (Glycine max (L.) Merrill)

Flower shedding in soybean, Glycine max (L.) Merrill, was studiedusing cultivar ‘Clark’, isoline E₁t, which has relativelylong racemes for convenient identification and observation ofindividual flowers. On each raceme studied, pod set was greatestat the proximal (basal) positions, whereas shedding was greatestat the most distal positions. When proximal flowers were removedas they reached anthesis, pod set increased at the more distalpositions. Pod set was increased in some instances by applicationof water directly to the ovaries as a drop in the calyx cup.Peroxidase activity changed in parallel with ovary development,increasing rapidly in growing pods but not in shedding flowers.Increases in flower peroxidase was mainly in ovary walls. Flowerstaken at or near anthesis from positions with high percent podset could be grown in vitro with especially good ovary enlargement,whereas ovaries in flowers taken from positions of low pod setdid not enlarge in culture. Unidentified substances were extracted from young pods which,when incorporated into lanolin and tested in an in situ bioassay,could mimic the effect of proximal flowers in inducing sheddingof distal flowers. Indole-3-acetic acid resembled the extractedmaterials in inducing shedding, but differed by eliciting side-effectsthat extracts did not. The growth substances abscisic acid,gibberellic acid, and benzyladenine did not promote sheddingin the in situ test. The evidence was taken to indicate that soybean flower sheddingis induced in distal flowers by substances from the more proximal,fertilized ovaries, and that this is possibly due to interferencewith some of the intense metabolic changes that follow pollinationand fertilization.     

拟寄生蜂的寄主标记研究进展

拟寄生蜂常借助寄主标记信息素 (host marking pheromone, HMP) 来辨别已寄生寄主和健康寄主,避免过寄生和多寄生,减少后代的种内和种间竞争。寄主标记有外部标记、内部标记和“容器”及区域标记3种方式。HMP来源于拟寄生蜂的杜氏腺、毒腺、输卵管、卵巢、卵或咽侧体,由触角或产卵器感受。目前已鉴定出几种拟寄生蜂的HMP,多数为饱和与不饱和烃类的混合物,但卡氏盾痣细蜂Dendrocerus carpenteri的HMP是保幼激素。拟寄生蜂对寄主标记的反应受HMP持效期,拟寄生蜂内部状况如载卵量、年龄、经验和学习,及外部条件如拟寄生蜂和健康寄主种群密度以及寄主种类的影响。本文还讨论了HMP研究的理论和实际意义。     

Growth of harmful marine algae in multispecies cultures

Mixtures of harmful and harmless algae were grown in discontinuouslydiluted batch cultures under ammonium, nitrate and phosphatelimitation, and at different irradiances (20–500 µjnolquanta m^–2 s^–1). The species used were Chrysochromulinapolylepis, Emiliania huxleyi type B, Rhodomonas sp., the dinoflagellalesFibrocapsa japonica, Gymnodinium simplex, Gyrodinium aure-olum,Heterocapsa triquetra, Heterosigma carterae, Prorocentrum micansand Alexandrium tamarense, the diatoms Chaetoceros socialis,Cymatosira belgica, Ditylum brightwellii, Laudcria borealis,Odon-telta aunla, Pseudonitzschia pungens, Streptotheca tamesis,and the cyanobacterium Synechococcus. Their growth responsein the mixed algal cultures is discussed in relation to theirabundance in different natural habitats. In comparison withthe other non-diatoms, the mixotrophic C.polylepis grew fastunder all tested nutrient and light limitations.Emiliania huxleyigrew well under nitrogen (N) limitation (with nitrate as N source)and at irradiance levels from 15 up to 500 µmol quantam^–2 s^–1. No growth of calcifying cells could bedetected under N limitation when ammonium was used as N source.Rhodomonas grew reasonably well under ammonium-N limitationand grew fast at the highest irradi-ance. The dinoflagellateswere poor competitors compared to the Prymnesiophyceae. Theenvironmental fitness of the Prymnesiophyceae appears to beclosely related to the reproductive capacity of the vegetativestage, whereas the natural distribution of dinoflagellates seemsmore closely dependent on the generative reproduction-relatedspecific life cycle characteristics of the individual species.The marine diatoms include a mixture of both types of species.Some marine diatom species clearly have the capability to outcompetenon-diatoms under different types of nutrient and light limitationswhen silicate is in excess. Other diatoms seem to be poor competitors.     

Experimental evidence for a neuroendocrine control of ecdysone biosynthesis in adult females of Locusta migratoria

The considerable increase in ecdysteroid concentration which occurs in normal Locusta ovaries at the end of each cycle of oöcyte maturation is prevented if the median neurosecretory cells of the pars intercerebralis are cauterized, or if the corpora cardiaca are excised 24 hr before the onset of ecdysone synthesis in normal females. Implantation of additional brain-corpora cardiaca complexes into young vitellogenic females advances the time of ecdysone synthesis by some 12 hr. Oöcyte growth itself is not affected in these different types of experiments.It is inferred from the data of the present study that ecdysone synthesis in the follicle cell epithelium of maturing Locusta ovaries is stimulated by a neurohormone produced in the median neurosecretory cells of the pars intercerebralis and secreted into the blood via the corpora cardiaca.     

Molluscan Metamorphosis: A Study in Tissue Transformation

Metamorphosis of the pelagic larvae of benthic marine invertebratesis often a cataclysmic event in which a rapid loss of organsspecialized for larval life occurs simultaneously with the renewalor increased rate of development of potential adult organs.In the nudibranch gastropod Phestilla sibogae this change involvesloss of the velum, shell, operculum, larval kidney, some retractormuscles, and some of the pedal mucous glands. Exit from thelarval shell at metamorphosis is rapid and is correlated withthe spread of epidermis from the larval foot over the visceralmass as the visceral mass emerges from the shell aperature.This spreading of epipodial epidermis to cover the entire bodyhas not been previously reported for other nudibranchs. Neithercell proliferation nor active cell motility are responsiblefor this epidermal migration. Rather it appears that the actionof larval muscles pulls the visceral organs out of the shelland simultaneously causes the epipodial epidermis to cover thevisceral mass. This epidermis becomes the definitive adult epidermis.     

Succession of bacterivorous protists on laboratory-made marine snow

Colonization and succession over time by bacterivorous protistson laboratory-made marine snow were analysed in five assaysduring 1994. Marine snow was made hom natural seawater usingrolling tanks. In all experiments, the macroaggregates werestable in size and consistency after the fourth day, and thecolonization and succession processes were similar. Newly formedmacre aggregates became colonized by heterotrophic nanoflagellateson the fourth day, mmt of them kinete plastids (Bodo designisand Rhynchomonns nasuta) and bicosoecids (Pseudobodo tremulansand Bicosoeca sp.). Sarcodines and ciliates appeared 1 day later.Among the former, the most abundant genus was Vannella sp.,while scuticociliates (Uronema marinum) and hypotrichs (Euplotesvannus and Aspidisca steini) were the most abundant ciliates.Most of the species observed in the study were more common tobenthic habitats than to pelagic ones. The planktonic existenceof the genera Bodo, Rhynchomonas, Bicosoeca, Euplotes and Aspidiscadepends on the presence of surfaces because they are poor swimmersor immotile, and Pseudobodo and Vannella need attachment forfeeding. The only pelagic protist observed was Uronema, probablybecause its opportunistic behaviour leads it to exploit enrichedenvironments such as marine snow. Flagellate and ciliate abundancesin laboratory-made macroaggregates were much higher than insurrounding water, which indicates that marine snow representsan enhanced habitat for protist growth.     

Limnocalanus macrurus (Copepoda: Calanoida) retains a marine arctic lipid and life cycle strategy in Lake Michigan

Limnocalanus macrurus, an omnivorous calanoid copepod with strongcarnivorous tendencies that invaded fresh water during the Pleistoceneglaciation, retains a marine arctic lipid and life cycle strategyin the hypolimnion of Lake Michigan. Its maximum lipid concentrationof 67% of dry mass—consisting largely of wax esters—isthe highest reported for freshwater zooplankton and is amongthe highest reported for marine polar species. The high lipidconcentration of L.macrurus runs counter to the paradigm thathigh wax ester concentrations are found in herbivorous, butnot in carnivorous, polar species. Lipids are drawn down toextremely low levels (10% of dry mass) during the reproductiveperiod, November–May. Reproduction in this univoltinespecies appears to be timed so that the new generation developsduring the high abundance of prey (crustacean microzooplanktonand net phytoplankton) in spring. A high wax ester content mayallow egg production to start in winter when the prey concentrationis low. In contrast to many polar species, the new generationmoves through all copepodid stages to adult without diapausing.Copepodid 5 females have a low lipid concentration, and lipidsare slowly built up in new generation adults during summer andfail before reproduction commences. This lipid and life cyclestrategy may have given L.macrurus an advantage over potentialfreshwater competitors, such as the arctic freshwater cyclopoidcopepod Cyclops scutifer, in the hypolimnia of glaciated lakes.     

Molecular diversity of bacterial production of the climate-changing gas, dimethyl sulphide, a molecule that impinges on local and global symbioses

This paper describes the ddd genes that are involved in theproduction of the gas dimethyl sulphide from the substrate dimethylsulphoniopropionate(DMSP), an abundant molecule that is a stress protectant inmany marine algae and a few genera of angiosperms. What is knownof the arrangement of the ddd genes in different bacteria thatcan undertake this reaction is reviewed here, stressing thefact that these genes are probably subject to horizontal genetransfer and that the same functions (e.g. DMSP transport) maybe accomplished by very different mechanisms. A surprising numberof DMS-emitting bacteria are associated with the roots of higherplants, these including strains of Rhizobium and some rhizospherebacteria in the genus Burkholderia. One newly identified strainthat is predicted to make DMS is B. phymatum which is a highlyunusual β-proteobacterium that forms N₂-fixing noduleson some tropical legumes, in this case, the tree Machaeriumlunatum, which inhabits mangroves. The importance of DMSP catabolismand DMS production is discussed, not only in terms of nutritionalacquisition by the bacteria but also in a speculative scheme(the ‘messy eater’ model) in which the bacteriamay make DMS as an info-chemical to attract other organisms,including invertebrates and other plankton. Key words: Acyl CoA transferase, Burkholderia, CLAW hypothesis, dimethyl sulphide, dimethylsulphoniopropionate, Marinomonas, nitrogen fixation, Rhizobium, rhizosphere, root nodules, Spartina Received 30 May 2007; Revised 27 September 2007 Accepted 1 October 2007     

Histology,histochemistry and morphometry of the ovary of the adult plains viscacha (Lagostomus maximus) in different reproductive stages

Lagostomus maximus is a South American Hystricognathi rodent whose reproductive behaviour shows characteristics unusual for mammals, such as polyovulation (200–800 oocytes) and a high rate of embryo mortality. Thirty‐six mature females captured in the province of Buenos Aires showed different physiological reproductive stages. Most of them presented a postpartum oestrus in August–September. This characteristic is different from that reported in other geographical areas. The stages considered were: anoestrus, follicular phase, early pregnancy and late pregnancy. The ovaries were light‐pink and smooth and presented a tortuous cord‐like aspect. Many primordial follicles were found in all the females studied. Follicles in different states of maturation and primary and accessory corpora lutea were observed in the cortex. These structures were smaller than those present in other related species. Follicles did not project into the surface of the organ. Calcified follicles of diverse size were found in all the ovaries. Atretic follicles were found in all the stages analysed. Interstitial tissue surrounding the follicles and the corpora lutea was also observed. The number and proportion of different cortical structures varied in the physiological stages analysed. The ovaries of the viscacha have differential characteristics in comparison to other Hystricognathi, some of them related to polyovulation.     

Endogenous Cytokinins in Developing Fruits of Seeded and Seedless Citrus Cultivars

This report describes the isolation and identification of endogenouscytokinins from Citrus ovaries. Cytokinin active fractions wereobtained by extraction with 80% (v/v) ethanol, followed by purificationwith hexane, n-butanol and a polyvinylpyrrolidone and SephadexLH-20 column chromatography. Five fractions with cytokinin activity were found in the organicphase, using the tobacco callus assay. The main active compoundsin these fractions were separated by HPLC, bioassayed and identifiedby GC—MS as ribosyl zeatin, zeatin and isopentenyl adenosine.Hydrolysis of the first fraction with B-glucosidase gave cytokininactive compounds that in paper chromatography had R_F's similarto those of zeatin and ribosyl zeatin. Treating the aqueousphase with alkaline phosphatase produced a cytokinin activecompound that in paper chromatography had the same R_F as isopentenyladenosine indicating that their ribotide was probably the majorphosphorylated cytokinin present in Citrus ovaries. Key words: Citrus, cytokinin fruit set and development     

Photoperiodic Regulation of Gametogenesis in Sea Stars, with Evidence for an Annual Calendar Independent of Fixed Daylength

SYNOPSIS. Gametogenesis and gonadal growth in the west coastsea star Pisaster ochraceus normally begins in the fall andleads to large gonads full of gametes in the spring, when spawningoccurs. The timing of gametogenesis can be shifted simply bymaintaining the animals on a seasonally changing photoperiodicregime out of phase with ambient. When they are kept on a spring-summerphotoperiodic regime during the fall and winter, gametogenesisproceeds 6 mo ahead of schedule in the following spring andsummer. Gametogenesis can be shifted out of phase even whenthe eyespots are removed. Short daylengths that normally occurduring the fall and winter are not required for gametogenesisto proceed, nor are even the long daylengths of spring and summerthat precede the initiation of gametogenesis in the fall. Thetemporal program is insensitive to fixed daylengths (LD 15:9,13:11, 12:12, 9:15) and appears to involve an endogenous calendar. Shifting the photoperiodic regime 6 mo out of phase also leadsto a shift of the gametogenic temporal program in the sea starsLeptasterias sp. (a brooder) and Asterias vulgaris (from theNew England coast), but not in the sea star Patiria miniata.Gametogenic timing also can be switched in the sea urchin Strongylocentrotuspurpuratus but the mechanism of the photoperiodic response isfundamentally different; gametogenesis requires short daylengths;continues indefinitely under a repeated short day, fall-winterphotoperiod regime, and apparently does not involve an endogenouscalendar. As photoperiodic responses are investigated furtherin these and other marine invertebrates, the models developedprimarily from studies on terrestrial organisms may need tobe extensively modified or additional new models required.     

Enolase from Trypanosoma brucei, from the amitochondriate protist Mastigamoeba balamuthi, and from the chloroplast and cytosol of Euglena gracilis: pieces in the evolutionary puzzle of the eukaryotic glycolytic pathway

Genomic or cDNA clones for the glycolytic enzyme enolase wereisolated from the amitochondriate pelobiont Mastigamoeba balamuthi,from the kinetoplastid Trypanosoma brucei, and from the euglenidEuglena gracilis. Clones for the cytosolic enzyme were foundin all three organisms, whereas Euglena was found to also expressmRNA for a second isoenzyme that possesses a putative N-terminalplastid-targeting peptide and is probably targeted to the chloroplast.Database searching revealed that Arabidopsis also possessesa second enolase gene that encodes an N-terminal extension andis likely targeted to the chloroplast. A phylogeny of enolaseamino acid sequences from 6 archaebacteria, 24 eubacteria, and32 eukaryotes showed that the Mastigamoeba enolase tended tobranch with its homologs from Trypanosoma and from the amitochondriateprotist Entamoeba histolytica. The compartment-specific isoenzymesin Euglena arose through a gene duplication independent of thatwhich gave rise to the compartment-specific isoenzymes in Arabidopsis,as evidenced by the finding that the Euglena enolases are moresimilar to the homolog from the eubacterium Treponema pallidumthan they are to homologs from any other organism sampled. Inmarked contrast to all other glycolytic enzymes studied to date,enolases from all eukaryotes surveyed here (except Euglena)are not markedly more similar to eubacterial than to archaebacterialhomologs. An intriguing indel shared by enolase from eukaryotes,from the archaebacterium Methanococcus jannaschii, and fromthe eubacterium Campylobacter jejuni maps to the surface ofthe three-dimensional structure of the enzyme and appears tohave occurred at the same position in parallel in independentlineages.