Structure of the dnaA region of the endosymbiont, Buchnera aphidicola, of aphid Schizaphis graminum

Buchnera aphidicola is an intracellular prokaryote (endosymbiont)that lives in the body cavity of the aphid. Phylogenetic studiesindicated that it is closely related to Escherichia coli andmembers of Enterobacteria. The gene order of the region containingthe dnaA gene is well conserved in many bacteria. Seven genesof the endosymbiont of the aphid Schizaphis graminum, gyrB,dnaN, dnaA, rpmH, rnpA, yidD, and 60K, were found to be homologousin sequence and relative location to those of E. coli. We havefurther sequenced the region downstream of the 60K gene to elucidatethe boundary of the conserved region, and found that one moregene, thdF , is conserved. The comparison of gene organizationsof the dnaA region of the related bacteria supported the closephylogenetic relationship of B. aphidicola to E. coli. In addition,we have identified groES and groEL genesnext to the thdF gene.GroEL protein was reported to be expressed at an elevated levelin the endosymbionts of aphids, and is considered to play animportant role in their association with the aphid host. Comparisonof the structure of the groE operon with that of the endosymbiontof the aphid Acyrthosiphon pisum revealed the conservation ofa sequence resembling the E. coli consensus heat shock promoter,and this sequence may be responsible for the high expressionof the groEL gene in aphid endosymbionts.     

Some Observations on the Diversity of Stomata and Trichomes in Six Species of Dioscorea

Stomata and trichomes are described on the leaves of six speciesof Dioscorea. As many as six types were found in D. bulbiferaand D. oppositifolia, four types in D.hispida and D. wallichii,three types in D. belophylla, but only two types in D. alata.Although there is a diversity of stomata even on the same surface,the predominant type is anomocytic in all the species exceptD. bulbifera in which it is tricytic. Rarely a stoma is alsocyclocytic in D. bulbifera. An increase in the number of subsidiarycells in paracytic, tricytic, or diacytic stomata takes placeby the wall formation in them. Similarly a reduction in thenumber of subsidiary cells of a tetracytic stoma is the resultof lateral subsidiary cells assuming the form of epidermal cells.Abnormalities such as a stoma with one guard cell, degenerationof guard cells, and contiguous stomata are also met with. Theorganization of different types of stomata is studied in D.bulbifera and D. wallichii and shown to be perigenous. Capitateglandular hairs were seen on the leaves of D. belophylla, D.bulbifera, D. hispida, and D. wallichii but non-glandular, uniseriate,3-celled trichomes were observed only in D. hispida.     

A Mechanistic Analysis of Self-thinning in Terms of the Carbon Balance of Trees

The self-thinning behavior of a monoculture forest is examinedfrom a mechanistic viewpoint, in terms of the carbon balanceof trees at the stand level. Two approaches are described: thefirst is based on simple assumptions concerning the balancebetween growth, photosynthesis and respiration; the second usesthe process-based I.T.E. EDINBURGH FOREST model, extended toinclude tree birth and death, to examined the assumptions ofthe first approach at a more mechanistic level and to interpretthe observed variation in the responses to shading and soilfertility in terms of a single model. The first approach leads to a power law relation m n ^-1/y betweenmean biomass per tree (m) and the number of trees per unit groundarea (n), where y is the exponent characterising the rate atwhich respiration (r) scales with biomass (i.e. r m^y). Forvalues of y less than 1, m and n are predicted to increase anddecrease, respectively, as powers of time (t) such that thebiomass per unit ground area (M) increases linearly with t forany value of y. When y equals 1, m and n vary exponentiallywith t and M remains constant. When r is assumed to be proportional to stem cambium surfacearea, the value of y is shown to lie in the range 0·5to 1 depending on the rate of stem taper. This leads to slopeson a log m vs. log n self-thinning plot in range -1 to -2 andtypically around -1·5 for rates of taper based on mechanicalrequirements. For the second approach, the I.T.E. EDINBURGH FOREST model,a previously published mechanistic model of plantation growthat the stand level (Thornley, 1991), is extended to naturalstands by introducing average stem birth and death rates thatare functions of the carbon and nitrogen substrate status oftrees. Growth of even-aged and mixed-age forest over about 500years is simulated under a variety of environmental and physiologicalconditions. In general, the forest model predicts a curved log m vs. logn thinning line, but has a reasonably well-defined linear sectionunder most conditions. The slope of the linear portion flattensas the rate at which cambium surface area scales with structuralbiomass increases, in qualitative agreement with the analyticalprediction of the first approach. Quantitative differences betweenthe two approaches are interpreted in terms of the process representedin the forest model. In general, the height of the thinningline increases with irradiance, but is relatively insensitiveto soil nitrogen, with no change in slope in either case. However,at very low irradiance or soil nitrogen levels, the slope flattenscontinuously and the entire thinning line becomes markedly non-linear.Even-aged stands and mixed-age stands have different thinningslopes.Copyright 1993, 1999 Academic Press Self-thinning, carbon balance, mechanistic model, forest growth, respiration     

The GUS reporter-aided analysis of the promoter activities of Arabidopsis ACC synthase genes AtACS4, AtACS5, and AtACS7 induced by hormones and stresses

Ethylene biosynthesis in higher plants is regulated developmentallyand environmentally. To investigate the regulation of ACC synthasegene expression, the promoters of Arabidopsis ACS genes, AtACS4,AtACS5, and AtACS7, were fused to a GUS reporter gene, and therecombinant transgenes were introduced into Arabidopsis to producethree groups of AtACS::GUS transgenic plants. Histochemic andfluorometric study of these transgenic plants revealed thatpromoters of AtACS4, AtACS, and AtACS7 are all active in dark-germinatedseedlings. AtACS5 has the highest promoter activity in leavesof 2-week-old light-grown seedlings among the three AtACS genesstudied. In the mature leaves, AtACS4 and AtACS7 genes are expressedin both veins and areoles, whereas AtACS5 is expressed at ahigher level in the areoles and epidermal cells surroundingtrichomes. The promoter activities of all these AtACS genesare found in the reproductive organs. AtACS5 and AtACS7 arehighly expressed in petals, sepals, carpels, stamens, caulineleaves, inflorescence stems, and siliques, while AtACS4 expressionis undetectable in the petals of open flowers. All three AtACSgenes are expressed in root tissue. In the 2-week-old light-grownArabidopsis, the AtACS4 promoter is responsive to the planthormones IAA, ethylene, and ABA, and to darkness and wounding;the AtACS5 promoter to IAA, ABA, salt, high temperature, andwounding; and the AtACS7 promoter to GA₃, ethylene, and ABA,and to darkness and salt. Low-temperature treatment abolishesthe darkness-induced AtACS7 gene expression, but not that ofAtACS4. Each AtACS gene has a unique expression profile duringgrowth and development. It appears that at any developmentalstage or any growth period of Arabidopsis, there is always amember of AtACS multigene family that is actively expressed. Key words: ACC synthase, Arabidopsis, ethylene, gene expression, GUS histochemical staining, reporter, stress treatments     

Genetic Diversity of the Wild Banana Musa acuminata Colla in Malaysia as Evidenced by AFLP

Musa acuminata Colla (Musaceae), the wild progenitor of thecultivated banana, is highly variable in Malaysia and presentsseveral unresolved nomenclatural problems. AFLP was employedto distinguish among three subspecies of Musa acuminata(subsp.truncata and subsp. malaccensis from peninsular Malaysia andsubsp. microcarpa from Borneo) and to examine whether subsp.truncata is a distinct taxon. Eight primer combinations revealedmolecular markers specific for each of the three taxa. UPGMAcluster analysis showed the three taxa were distinct. Subspeciesmalaccensis which is endemic in peninsular Malaysia and subsp.microcarpa which is endemic in Borneo were found to be moresimilar to each other in their DNA patterns than they are tosubsp. truncata, which is endemic to peninsular Malaysia. Sincesubsp. truncata is genetically separate from subsp. malaccensisand subsp.microcarpa , it cannot be regarded as synonymous witheither of these subspecies. This paper sheds light on the nomenclatureof the three subspecies of Musa acuminata. Copyright 2001 Annalsof Botany Company Musa acuminata Colla, truncata, malaccensis, microcarpa, Musaceae, wild banana, genetic diversity, AFLP, DNA fingerprinting     

FLC or not FLC: the other side of vernalization

Vernalization is the promotion of the competence for floweringby long periods of low temperatures such as those typicallyexperienced during winters. In Arabidopsis, the vernalizationresponse is, to a large extent, mediated by the repression ofthe floral repressor FLC, and the stable epigenetic silencingof FLC after cold treatments is essential for vernalization.In addition to FLC, other vernalization targets exist in Arabidopsis.In grasses, vernalization seems to be entirely independent ofFLC. Here, the current understanding of FLC-independent branchesof the vernalization pathway in Arabidopsis and vernalizationwithout FLC in grasses is discussed. This review focuses onthe role of AGL19, AGL24, and the MAF genes in Arabidopsis.Interestingly, vernalization acts through related molecularmachineries on distinct targets. In particular, protein complexessimilar to Drosophila Polycomb Repressive Complex 2 play a prominentrole in establishing an epigenetic cellular memory for cold-regulatedexpression states of AGL19 and FLC. Finally, the similar networktopology of the apparently independently evolved vernalizationpathways of grasses and Arabidopsis is discussed. Key words: AGL19, Arabidopsis, chromatin, epigenetics, FLC, flowering time, polycomb, PRC2, vernalization Received 19 December 2007; Revised 11 February 2008 Accepted 15 February 2008     

Revision of the Genus Goodallia (Bivalvia: Astartidae) with the Description of Two New Species

A revision of the Recent species of the genus Goodallia (Astartidae)is presented. Adult shell and prodissoconch morphology of allthe species are described and figured. In total, five speciesare recognized: G. triangularis (Montagu, 1803), G. pusilla(Forbes, 1844), G. macandrewi (Smith, 1881), G. micalii new species,and G. gofasi new species. G. triangularis and G. pusilla are widespreaddistributed in the Atlantic coasts of Europe and North Africa,and in the Mediterranean. G. macandrewi is restricted to thetype locality in the Canary Islands, while what has been calledG. macandrewi from the Mediterranean corresponds to an undescribedspecies here named G. micalii, distributed in the Central andEastern Mediterranean. A second undescribed species from offthe Atlantic Moroccan coast is named G. gofasi, and is knownonly from the type material of station B33 of the expedition CINECA CHARCOT III. The named forms, variability and distributionof G. triangularis are discussed. (Received 30 January 1998; accepted 27 August 1998)     

Molecular Cytogenetics of the Genus Arabidopsis: In situ Localization of rDNA Sites, Chromosome Numbers and Diversity in Centromeric Heterochromatin

We have used in situ hybridization to determine the number ofsites of rDNA in species in the genus Arabidopsis. A. wallichii(2n = 16) has one major pair of sites and one minor pair ofsites, while A. pumila and A. griffithiana (both 2n = 32) havesix major and two minor rDNA sites. A. thaliana (2n = 10) isknown to have two pairs of rDNA sites. a highly repeated para-centromericsequence from A. thaliana, pAL1, is absent in the other threespecies. Hence the A.thaliana genome is not present (or thecentromeric DNA has evolved substantially) in the polyploidspecies A. pumila and A. griffithiana. Analysis of Arabidopsisspecies is a valuable complement to the large programmes forgenetic analysis of A. thaliana.Copyright 1993, 1999 AcademicPress Arabidopsis, centromeric DNA, maps (genetic), nuclear architecture, repetitive DNA, ribosomal DNA, rDNA, evolution, Brassicaceae, Crucifereae, in situ hybridization     

Evaluation of nitrogen fixation in the diatom genus Rhizosolenia Ehr. in the absence of its cyanobacterial symbiont Richelia intracellularis Schmidt

Aggregates of two species of Rhizosolenia (R. castracanei andR. imbricata var. shrubsolei) have been reported to containendosymbiotic bacteria and to fix nitrogen. The general importanceof this process to the genus is not known, although of greatpotential significance. Clonal cultures of five species of Rhizosolenia(R. alata, R. bergonii, R. calcar-avis, R. imbricata var. shrubsoleiand R. setigera) were examined for nitrogen fixation using acetylenereduction and compared to cyanobacterial controls. Mecososmaggregates of R. imbricata var. shrubsolei were tested, as wellas chains of R. debyana hand-collected using SCUBA. The Rhizosoleniaspecies did not contain the endosymbiotic cyanobacterium Richeliaintracellularis and were not examined for the presence of endosymbioticbacteria. Nitrogen fixation was not found in the Rhizosoleniaspp.; in contrast, the diazotrophic cyanobacterial controlsOscillatoria erythraea and Anabaena sp. reduced acetylene atsignificant rates. The absence of nitrogen fixation in the Rhizosoleniaspp. suggests diazotrophy by endosymbiotic bacteria is not widespreadin the genus Rhizosolenia, nor is it necessary for survivalof these large diatom cells in nutrient-poor, near-shore waters.     

Origin and evolution of a myxozoan worm

Buddenbrockia plumatellae is an active, muscular, worm-shapedparasite of freshwater bryozoans. This rare and enigmatic animalhas been assigned to the Myxozoa on the basis of 18S ribosomalDNA sequences and the presence of malacosporean spores. Herewe report cloning of four homologous protein-coding genes fromBuddenbrockia worms, the putatively conspecific sac-shaped parasiteoriginally described as Tetracapsula bryozoides and the relatedsac-shaped parasite Tetracapsuloides bryosalmonae, the causativeagent of proliferative kidney disease in salmonid fish. Analysesare consistent with the hypothesis that Buddenbrockia is indeeda malacosporean myxozoan, but do not provide support for conspecificitywith either T. bryozoides or T. bryosalmonae. Implications forthe evolution of worm-like body plans in the Myxozoa are discussed.     

Flowering in Pisum: the Effect of Age on the Gene Sn and the Site of Action of Gene Hr

Late cultivars of peas behave as quantitative long day plants.The reason that they flower between nodes 20 and 35 under an8 h photoperiod is shown to be because the leaves and maturestem produce a more promotory ratio of the flowering hormonesas they age. Later formed leaves may also start with a slightlymore promotory ratio than the leaves produced at a lower node.The gene Sn controls the production of a flower inhibitor andit is suggested that the activity of this gene in a leaf isgradually reduced as the leaf ages. From grafting experiments,the site of action of the gene Hr is shown to be in the leavesor mature stem and not at the shoot apex. This supports a previoussuggestion that the gene Hr is a specific inhibitor of the ageingresponse of gene Sn. Gene Hr is shown to cause a substantial delay in the floweringnode of decotyledonized plants of genotype If e sn hr undershort day conditions, suggesting that Hr has little effect inthe cotyledons. It is argued that the gene sn is a leaky mutantand that gene Hr does not control a photoperiod response inits own right but has its effect through the Sn locus. From a comparison of intact plants and self-grafts of the lategenotype If e Sn hr it is shown that under the conditions usedphysiological age may be of more importance than chronologicalage in determining flowering in peas. Reasons for the smalleffect of defoliation treatments on flowering are discussedas well as possible reasons for the promotory effect of decotyledonizationon the flowering node of late lines. Pisum sativum L, flowering, ageing, genetic control     

Effect of Water Stress on Pigment Formation in Quercus Species

The effect of water stress in three Quercus species belongingto different habitats is investigated. Chlorophyll concentrationdecreased in all Quercus species with the greatest decreaseoccurring in Quercus robur. An increase of total carotenoidcontent was observed in Quercus coccifera and Quercus ilex,while in Q. robur water stress effected a carotenoid contentreduction. Anthocyanins increased with decreasing relative watercontent in the three Quercus species, the largest increase occurringin Q. coccifera. A correlation between xerophytic characterand pigment concentration is discussed.     

Development of Axillary and Leaf-opposed Buds in Rattan Palms

Axillary vegetative buds are present in Calamus, Ceratolobus,and Plectocomiopsis. Two species of Daemonorops Sect. Piptospathaalso have axillary vegetative buds. All species of Daemonoropshave only displaced adnate axillary inflorescence buds. A singlebud is initiated in the axil of the first or second leaf primordiumin a way similar to that for axillary inflorescence buds. Themeristem is displaced during development on to the internodeabove and sometimes on to the base of the leaf above. Leaf-opposedvegetative buds occur in five species of Daemonorops Sect. Cymbospathaand in one species of Daemonorops Sect. Piptospatha. This typeof bud is initiated 180° away from the axil of the firstor second leaf primordium. It is not a displaced axillary bud,but does become adnate to the internode above like the axillarybuds. One or more leaves, transitional between juvenile andadult, on a shoot often subtend both types of buds. Myrialepishas leaf-opposed vegetative buds, but their development wasnot observed. Korthalsia has buds that are displaced about 130°from the leaf axil and are intermediate between the axillaryand the leaf-opposed condition. Other forms of vegetative budsare described: multiple buds in Plectocomia, aerial forkingin Korthalsia, and suckering from inflorescences and from aerialstems in Calamus. bud development, rattan palms, palm taxonomy, branching     

Origin of Epidermis and Development of Root Primordia in Pistia, Hydrocharis and Eichhornia

All three floating plants have roots bearing laterals derivedfrom both pericycle and endodermis. In Pistia and Eichhornialaterals arise within the meristem of the mother root; in Hydrocharisthey arise from mature tissue. In Pistia and Hydrocharis theepidermis becomes anatomically discrete between cortex and cap:in Pistia it is derived from the endodermis of the mother root,in Hydrocharis from the pericycle. The epidermis is not discretein Eichhornia and is derived from the pericycle of the motherroot with the cortex. Stathmokinetic data were used to construct timetables of developmentwhich show how the differences arise. In Pistia the first periclinaldivision of the endodermis-derived tissue individualizes theepidermis and occurs early, before a quiescent centre forms.In Hydrocharis the epidermis also becomes discrete before thepole of the meristem becomes quiescent, but it does so by apericlinal division of the pericycle-derived tissue. In Eichhorniapericlinal divisions occur in the outermost layer of the pericycle-derivedtissue long after quiescence has set in at the pole and afterthe fourth periclinal division in the endodermis derived cap.Its epidermis therefore never becomes anatomically discretethough it becomes functionally discrete because its polar cellsstop dividing as in the other plants. The involvement of the endodermis of mother roots in the formationof laterals is discussed in relation to the state of differentiationat sites of primordium formation, discreteness of the epidermisand subsequent fate of primordia. Pistia stratiotes L., Hydrocharis morsus-ranae L., Eichhornia crassipes Solms., primordia, lateral root, discrete epidermis, development, chimera, stathmokinetics     

Coupling of nauplii release in barnacles with phytoplankton blooms: a parallel strategy to that of spawning in urchins and mussels

We examined the coupling between the release of nauplii in Semibalanusbalanoides and phytoplankton blooms, and compared it with themechanism synchronizing spawning with phytoplankton abundancein green sea urchins (Strongylocentrotus droebachiensis) andblue mussels (Mytilus edulis). Close contact with phytoplanktoncells is required to stimulate the release of nauplii in Semibalanus,whereas spawning in urchins and mussels is triggered by an extracellularmetabolite of phytoplankton. The response is concentration dependentand positively correlated with the frequency of moulting Themoulting rate in Semibalanus is reported to be directly correlatedwith food intake and thus larval release should be proportionalto feeding activity. The release of Semibalanus nauplii is morestrongly stimulated by the diatom Skeletonema costatum thanby Phaeodactylum tricornutum, whereas the highest response isobtained in treatments with nauplii of Artemia salina. We suggestthat these differences are related to size of the planktonicparticles (Artemia nauplii < Skeletonema < Phaeodactylum)Exposure to air, as occurs in the intertidal zone, does notinfluence significantly larval release Larval release in otherCrustacea may similarly be coupled to phytoplankton abundance.     

Structure and Development of Stomata on the Vegetative and Floral Organs of Some Amaryllidaceae

The structure and development of stomata in 10 Amaryllidaceousmembers are described. The study is made on the leaves and floralorgans of Amaryllis belladona, Crinum asiaticum, C. bulbispermum,C. latifolium, C. pratense, Pancratium sp., Polianthes tuberosa,and Zephyranthes atamsco, and on leaves of Agave sp. and Curculigoorchioides. In most of the organs of the different plants studiedmore than one type of stoma occur, even on the same surface.However, the stomata are largely anomocytic in Amaryllis, Crinum,Pancratium, Polianthes, and Zephyranthes, but they are tetracyticin Agave and Curculigo. An increase in the number of subsidiarycells in teracytic, tricytic, paracytic, and stomata with onesubsidiary cell has been noted. It may be due to wall formationin the subsidiary cells or by the neighbouring perigenes assumingtheir form. The range of variation in different types of stomatain each organ has been studied. Abnormal features such as juxtaposedor superimposed contiguous stomata, connections between guardcells of nearby stomata, transformation of meristemoids intoepidermal cells are observed. The development of different typesof stomata in different organs of the same plant is perigenous.The systematic position of different genera is discussed inlight of the present findings. A method of preparing epidermalimprints by the use of Depex, a mounting medium, and white ofan egg is also described.     

A Study of the Evolutionary Relationships of Fundulus Topminnows (Teleostei: Fundulidae)

A hypothesis of the evolutionary relationships of thirty-fourspecies of Fundulus and their closer relatives is presented.The study is restricted to morphological characters which couldbe determined to be primitive or derived using the methods ofphylogenetic systematics. Following Parenti, a family Fundulidaeis recognized. It is composed of four genera of North Americankillifishes. (Cyprinodontidae as usually constitutedis polyphyletic.)No convincing characters demonstrate that Fundulus is a naturalgroup (a monophyletic group). However, all species of Fundulusshare four derived characters with Lucania. The sister group(closest genealogical relative) of Fundulus plus Lucania isa group composed of the genera Adinia and Leptolucania. Fourmonophyletic groups of Fundulus can be recognized based on sharedderived characters: (1) subgenus Fundulus (seven species excludingthree species placed in Fontinus); (2) subgenus Fonlinus (sixspecies); (3) subgenus Xensima (five species); and (4) subgenusZygonectes (thirteen species). Three species, F. (Plancterus)zebrinus, F. lima, and F. parvipinnis are of uncertain affinitieswithin the Lucania-Fundulus clade     

A review of European 'Mysella' species (Bivalvia, Montacutidae), with description of Kurtiella new genus

The type species of the genera Mysella Angas, 1877, RochefortiaVélain, 1878, Rochefortula Finlay, 1927 and AltenaeumSpaink, 1972 are illustrated and discussed. A new genus Kurtiellais introduced for ‘Mysella’ bidentata (Montagu,1803) and other European species currently placed in Mysella.These species display a unique diagnostic character state inhaving the cardinal platform deeply receding to house the internalligament, along with an array of more general montacutid traits.At the species level, diagnostic characters are given for thetype species K. bidentata, and for other included species K.ovata (Jeffreys, 1881), K. pellucida (Jeffreys, 1881), K. triangularis(Watson, 1897) and K. tumidula (Jeffreys, 1866), based mostlyon characters of the prodissoconch and on shell outline. Montacutasimillima Smith, 1892, from St Helena, is considered a juniorsynonym of K. pellucida. The loss of labial palps in K. tumidulais interpreted as a further derived character, which does notconflict with the generic placement in Kurtiella. (Received 28 August 2007; accepted 1 December 2007)