A Conceptual Framework for Biology Part I

These essays are part of the sixth yearly presentation of aneducational project of the American Society of Zoologists. Thepurpose is to provide background materials for those who teachthe first-year biology courses in colleges and universities.The Science as a Way of Knowing project emphasizes the conceptualframework of the biological sciences, shows how scientific informationis obtained and validated, and relates science to human concerns.The topic for consideration this year is Cell and MolecularBiology.     

A DEMOGRAPHIC ANALYSIS OF y-NEOTRICULA APERTA (GASTROPODA: POMATIOPSIDAE) POPULATIONS IN THAILAND AND SOUTHERN LAOS, IN RELATION TO THE TRANSMISSION OF SCHISTOSOMIASIS

The results of field work undertaken along the tropical reachesof the Mekong river in Thailand and Laos are presented. Demographicdata concerning the schistosome-transmitting snail y-Neotriculaaperta are examined and related to the life-cycle of this species.On the basis of these data, and a review of the literature,the only available, empirically substantiated, model for thelife-cycle of y-N. aperta (see Upatham et al., 1980) is shownto be equivocal. In this model snails survive the annual spatein the Mekong river as eggs, which remain dormant below theflood waters, whilst the adults die soon after the waters beginto rise. Here, the above described model of ‘egg survival’is shown to fail to balance the demographic equation for y-N.aperta. An alternative model of delayed oviposition with post-spatesurvival of mature snails is proposed and shown to be a betterfit to the available data. The implications of this alternativemodel for the evolutionary biology and ecology of N. apertaare discussed. The possible effects of the Pak-Mul dam project(Northeast Thailand) on local populations of schistosome-transmittingsnails are assessed and the hydrodynamic conditions conduciveto vector snail proliferation are considered. Attenuation ofthe normal flood-cycle of the Mekong river anc alteration ofthe river bed topography will probably lead to increased numbersof N. aperta at Pak-Mul. These changes, together with the influxof casual labour from endemic areas in Laos, may result in anepidemic of human schistosomiasis in Northeast Thailand. (Received 18 April 1994; accepted 23 June 1994)     

Behavioral and Electrophysiological Studies on Chemoreception in Aplysia

Using the typical mouth opening response (MOR) as the indexof chemore-ception, several amino acid constituents of naturalfood for Aplysia were effective in eliciting MOR in concentrationsas low is 10^–6 10^–7 M (glutamic acid) and 10^–510^–6 M (aspartic acid). It was suggested that these substancesmay serve as food attractants for this animal. Combined resultsof behavioral and electrophysiological experiments indicatedthat the most sensitive food receptors of Aplysia are predominantlylocated in the anterior tentacular groove area of the oral veil.These receptors appeared to strongly project to the caudal darkcell clusters of the cerebral ganglion. Extracellular recordingof single afferent units following oral veil stimulation withvarious chemicals showed that the chemoreceptors in the anteriortentacular groove area were 100 to 1000 times more sensitiveto food substances than other stimuli tested. It was suggestedthat these receptors are relatively "specific" to food attractants.There was a correlation between behavioral and electrophysiologicalthreshold data for the individual compounds. The electrophysiologicalthresholds however were 5–15 times higher than the behavioralthresholds.     

Cloning and Sequencing of a 36-kb Region of the Bacillus subtilis Genome between the gnt and iol Operons

Within the framework of an international project for the sequencingof the entire Bacillus subtilis genome, a 36-kb chromosome segment,which covers the region between the gnt and iol operons, hasbeen cloned and sequenced. This region (36447 bp) contains 33complete open reading frames (ORFs; genes) including the fourgnt genes and one partial gene. A homology search for the productsof the 33 complete ORFs revealed significant homology to knownproteins in 16 of them such as tetracycline resistance protein(Clostridium perfringens), asparagine synthetase (Arabidopsisthaliana), aldehyde dehydrogenase (Pseudomonas oleovorans),2,5-dichloro-2,5-cyclohexadiene-1,4-diol dehydrogenase (P. paucimobilis),heat shock protein HtpG (Escherichia coli), galactose-protonsymporter (E. coli), auxin-induced protein (common tobacco),glucitol operon repressor (E. coli) and methylmalonate-semialdehydedehydrogenase (P. aeruginosa). Unlike the regions we sequencedso far, this region contained two short sequence multiplications:one was a tandem sequence duplication (409 and 410 bp), andthe other a triplication consisting of two highly conserved118-bp tandem sequences preceded by a less conserved similarsequence (129 bp). The reasons for the presence of these sequencemultiplications in the gnt to iol region were deduced.     

Differential Expression of an Auxin-Regulated Gene, parC, and a Novel Related Gene, C-7, from Tobacco Mesophyll Protoplasts in Response to External Stimuli and in Plant Tissues

As part of an extended search for auxin-regulated genes otherthan parA and parB in the cDNA library from cultured tobaccomesophyll protoplasts, we have isolated the cDNA for a genedesignated parC. This gene is expressed during the transitionfrom the G₀ to S phase of the cell cycle. The nucleotide sequenceof parC cDNA was similar to that of parA. Using the parC cDNAas a probe we have isolated cDNA for a gene designated C-7 byhybridization at reduced stringency. Even though C-7 is relatedto parC, as is parA, its mode of expression was, to our surprise,completely different from that of parC. The C-7 gene is predominantlyexpressed in mature leaves and in freshly prepared protoplasts,but its level of expression did not change in response to auxintreatment. Although parC and C-7 are related to one anotherand exhibit homology to the parA gene, the two former genesdemonstrated conspicuous differences in their responses to externalstimuli, which included auxin, as well as their tissue-specificexpression. These results provide us an interesting system forthe analysis of the differential expression of closely relatedgenes. The significance of our observations is discussed withreference to the other members of the family of parA genes. (Received May 8, 1992; Accepted June 17, 1992)     

Long-range Perspectives on Neurobiology and Behavior

This essay is part of the seventh presentation of a yearly educationalproject of the American Society of Zoologists. The purpose isto provide background materials for those who teach the first-yearbiology courses in colleges and universities. The Science asa Way of Knowing project emphasizes the conceptual frameworkof the biological sciences, shows how scientific informationis obtained and validated, and relates science to human concerns.The topic for consideration this year is Neurobiology and Behavior.The introductory essay is concerned mainly with the conceptualframework of neurobiology, as developed over the ages, and afew examples of behavioral studies which can be related to neurobiologyor which are of special interest through links to human considerationsand problems.     

A water channel of the nematode C.elegans and its implications for channel selectivity of MIP proteins

A genome project focusingon the nematode Caenorhabditis elegans has demonstrated thepresence of eight cDNAs belonging to the major intrinsic proteinsuperfamily. We functionally characterized one of these cDNAs namedC01G6.1. Injection of C01G6.1 cRNA increased the osmotic waterpermeability (P_f) of Xenopusoocytes 11-fold and the urea permeability 4.5-fold but failed toincrease the glycerol permeability. It has been speculated that the MIPfamily may be separated into two large subfamilies based on thepresence or absence of two segments of extra amino acid residues (~15amino acids) at the second and third extracellular loops. BecauseC01G6.1 (designated AQP-CE1), AQP3, and glycerol facilitator (GlpF) all have these two segments, we replaced the segments of AQP-CE1 with thoseof AQP3 and GlpF to identify their roles. The functional characteristics of these mutants were principally similar to that ofwild-type AQP-CE1, although the values of P_f andurea permeability were decreased by 39-74% and 28-65%,respectively. These results suggest that the two segments of extraamino acid residues may not contribute to channel selectivity orformation of the route for small solutes.

     

A Circadian Rhythm in the Level of the Carbon Dioxide Compensation Point in Bryophyllum and Coffea

Measurements of CO² compensation were made over long periodsof time for Coffea arabica and Bryophyllum daigremontianum.For each species there was a marked rhythm in the level of CO²compensation, even though all major factors of the environmentwere held as constant as possible. The rhythm in Coffea wassusceptible to phase-shift and had a period slightly greaterthan 24 h. The rhythm in Bryophyllum had a period of c. 23 h.These observations show that the rhythm is probably endogenousin nature.     

An 8 kb Nucleotide Sequence at the 3' Flanking Region of the sspC Gene (184{degrees}) on the Bacillus subtilis 168 Chromosome Containing an Intein and an Intron

As part of the Bacillus subtilis genome sequencing project,we determined the complete nucleotide sequence of an 8000-bpfragment downstream of the sspC gene (184°) of the B. subtilis168 chromosome. The sequence analysis shows that the sspC geneis located inside of the SPß region, which differsfrom the current genetic map of B. subtilis 168. This regioncontains 12 putative ORFs (yojQ through yojZ and sspC). A homologysearch for the deduced products of the ORFs shows signi.cantsimilarities to enzymes involved in deoxyribonucleotide metabolism:ribonucleotide reductase (Nrd) E, NrdF, thioredoxinand dUTPase.Interestingly, this DNA fragment includes two split genes, yojPcontaining conserved motifs of an intein and yojQ and yojS withan 808-bp intervening sequence for a putative intron structure.In addition, the yojR gene includes a putative new DNA replicationterminator.     

Discovery Of Genetically Distinct Sympatric Lineages in the Freshwater Mussel Cyprogenia Aberti (Bivalvia: Unionidae)

The western fanshell, Cyprogenia aberti, occurs in the CentralHighlands region of North America and is the only congener ofthe federally endangered fanshell, C. stegaria. Due to a reductionin range size and local extirpations, extant populations ofC. aberti have become increasingly isolated. Consequently, C.aberti has been the focus of numerous conservation efforts,yet no work has examined the degree of genetic variation amongthe species' disjunct populations. Phylogenetic analyses ofnucleotide sequences from two mitochondrial gene portions (CO1and ND1) revealed results important to the conservation managementof C. aberti. First, phylogenetic analyses do not support amonophyletic C. aberti. Second, C. aberti is comprised of asmany as five independent lineages, one of which includes thefederally endangered C. stegaria. Third, analysis recoveredtwo genetically distinct sympatric lineages of C. aberti inthe Ouachita River Drainage. These phylogenetic results suggestthat the five distinct evolutionary lineages of C. aberti shouldbe managed as separate conservation units. This study illustrateswhy it is critical to evaluate genetic variability in endangeredand threatened ‘species’ prior to implementing arecovery program. These data also reveal the value of assessingbiological diversity of nonimperiled taxa before populationsare extirpated and valuable genetic data necessary for reconstructionof evolutionary relationships is lost. (Received 24 October 2005; accepted 8 June 2006)     

Enhancement of Peroxidase-Dependent Oxidation of Sinapyl Alcohol by an Apoplastic Component, 4-Coumaric Acid Ester Isolated from Epicotyls of Vigna angularis L.

A water-soluble component that enhanced the peroxidase-dependent(POX-dependent) oxidation of sinapyl alcohol was isolated fromepicotyls of Vigna angularis. This compound was an ester of4-coumaric acid and a hexose, and it was found in both the apoplastand the symplast. The ester was oxidized by a basic POX isozyme(K_m, about 20 µM) and by an acidic POX isozyme (K_m, about40 µM) that had been partially purified from the apoplasticfraction of epicotyls of V. angularis. These POX isozymes oxidizedsinapyl alcohol at only a very low rate, but a 15-fold enhancementwas observed upon addition of the ester. The concentrationsof the ester required for the half-maximal enhancement weresimilar to the K_m values of the ester for its oxidation by therespective isozymes. The apoplastic concentration of the esterwas higher than 130 µM, suggesting that this ester mightact as a donor of electrons to the apoplastic POX isozymes insitu. Coniferyl alcohol also enhanced the POX-catalyzed oxidationof sinapyl alcohol. The concentrations of coniferyl alcoholrequired for half-maximal enhancement of the oxidation of sinapylalcohol were about 23 and 250 µM when reactions were catalyzedby the basic and acidic POXs, respectively. These values weresimilar to the K_m values of coniferyl alcohol for its oxidationby the respective isozymes. These results suggest that 4-coumaricacid ester and coniferyl alcohol, if it is present in the apoplast,can enhance the POX-dependent oxidation of sinapyl alcohol inthe apoplast of epicotyls of V. angularis. (Received July 1, 1996; Accepted February 5, 1997)     

Cloning and Sequencing of a 23-kb Region of the Bacillus subtilis Genome between the iol and hut Operons

Within the framework of an international project for the sequencingof the entire Bacillus subtilis genome, a 23-kb chromosomalsegment, which covers the region between the iol and hut operons,has been cloned and sequenced, creating a 99-kb contig fromthe gnt operon to the wapA locus. This region (23351 bp) contains25 complete open reading frames (ORFs; genes) including deoR,dra, nupC and pdp and two partial ones. The region (5140 bp)containing these four genes, being also sequenced by H. H. Saxildet al., was sequenced by subjecting a long polymerase chainreaction product to random sequencing using phage M13mp19. However,we could detect no conflict, between two independently determinedsequences, which could be attributed to our sequencing method.A homology search for the 24 newly identified gene productsrevealed significant homology to known proteins in 14 of them.It was notable that three proteins, encoded by the successivegenes (yxeMNO), exhibited meaningful homology to the E. coliGlnHPQ products constituting a periplasmic ATP-dependent transportsystem for glutamine.     

The Influence of Genes ar and n on Senescence in Pisum sativum L.

The effect of genes ar (violet flowers, small hilum) and n (thick,fleshy pod wall) on whole plant in senescence peas was examinedby comparing Ar- with arar and N- with nn plants in segregatingprogenies. Homozygosity for ar or n significantly delayed the time whenthe plants were ready for harvest of their entire seed crop.These genes did not delay either the onset of reproduction orthe onset of apical arrest in the first instance. However, whereasAr- N- plants almost invariably senesced and died as the firstseed crop matured, the majority of arar and/or nn plants entereda period of secondary growth and a further fruiting cycle. Comparedwith Ar- plants, arar plants had over twice as many pods andseeds but individual seeds were 58 per cent lighter and totalseed yield (wt) was 19 per cent less. Pod length was unaffected.Compared with N-plants, nn plants had shorter pods (16 per cent),fewer seeds per pod (21 per cent), smaller seeds (20 per cent)and a lower total seed yield (wt 14 per cent less). It appearsthat ar and n impose a lower metabolic drain per reproductivenode as a consequence of their effects on hilum anatomy andpod morphology, respectively. These mutants disrupt the normalpattern of monocarpic senescence by breaking the coordinationbetween apical arrest and subsequent events. The developingseed crop delimited by the first arrest fails to cause plantdeath, possibly because sink size is less than in normal counterparts. Pisum sativum L, garden pea, senescence, hilum, pod, seed size, genetics     

Hair Curling Induced in Heterologous Legumes and Monocots by Flavonoid-Treated Rhizobia

The curling of root hairs and the deformation response wereobserved when white clover was infected with homologous strainsof Rhizobium leguminosarum biovar trifolii 4S and 0403. In thecase of Rhizobium meliloti NZ and Rhizobium leguminosarum biovarviciae 128C53, however, curling was only induced when thesebacteria were pretreated with flavonoids: luteolin in the caseof R. meliloti and naringenin for R.I. viciae. The same resultswere obtained with oat, a monocotyledonous non-leguminous plant.The two flavonoids mentioned are secreted from the host plantsand induce the expression of genes for root hair curling (Hac)on Sym plasmid in homologous rhizobia, therefore, the curlingresponse in both white clover and oat appears to be correlatedwith the activation of the Hac genes. These results suggestthat a factor(s) that activates the Hac genes, such as 7,4'-dihydroxyflavonewhich is known as the factor required by R. I. trifolii, issecreted from the oat roots. (Received June 12, 1989; Accepted November 9, 1989)     

Sequence Analysis of the 36-kb Region Between gntZ and trnY Genes of Bacillus Subtilis Genome*

Within the framework of an international Bacillus subtilis genomesequencing project, we have determined a 36-kb sequence coveringthe region between the gntZ and trnY genes. In addition to fivegenes sequenced and characterized previously, 27 putative proteincoding sequences (open reading frame; ORF) were identified.A homology search for the newly identified ORFs revealed thatsix of them had similarities to known proteins. It is notablethat new ORFs belonging to response-regulator aspartate phosphatase(Rap) and its regulator (Phr) families, and response regulatorand sensory kinase families of two-component signal transductionsystems have been identified. Furthermore, we found that some180-bp non-coding sequence, that might be an remnant of an ancientIS element, is preserved in at least five loci of the B. subtilisgenome.     

Science as a Way of Knowing--Human Ecology

This essay is part of the second presentation of an educationalproject of the American Society of Zoologists. The purpose ofthe project is to offer suggestions for improving the first-yearbiology courses in the universities. The method consists ofemphasizing the conceptual framework of the biological sciences,showing how scientific information is obtained and evaluated,pointing out the strengths and limitations of scientific procedures,and above all showing the relevance of science for human hopesand welfare. Each year a major topic will be considered. Lastyear it was Evolutionary Biology. This year it is Human Ecology.     

THE GENUS TRICOLIA IN THE EASTERN ATLANTIC AND THE MEDITERRANEAN

The genus Tricolia(Phasianellidae) in the Eastern Atlantic andMediterranean is reviewed on the bases of radular morphology,shell characters and polychromatism. The taxa included within the T. pullus (L.) group are not clearlyseparable and are treated as geographical subspecies:T. pulluspullus (L.), T. pullus picta (da Costa), T. pullus azorica (Dautzenberg),T. pullus canarica Nordsieck. The case of T. tenuis (Michaud)is problematic since it is clearly separable from sympatricT. pullus pullus in most parts of the Mediterranean but transitionalto T. pullus picta, towards the Atlantic. Other taxa are considered as having specific status since theyare consistently separable when found in sympatric populations.These include T. speciosa (Muhlfeldt), T. miniata (Monterosato),T. tingitana n.sp., T. petiti (Craven), T. nordsiecki (Talavera)and T. algoidea (Pallary). The last two species are stated forthe first time as belonging to the Phasianellidae. The genusEpheriella Pallary, based on T. algoidea, is synonymized withTricolia. (Received 6 April 1981;     

Flower Morphology and Pollination Mechanism in Three Sympatric Goodyerinae Orchids from Southeastern Brazil

The pollination biology of Aspidogyne argentea, Aspidogyne longicornuandErythrodes arietina was studied in south-eastern Brazil.The three species are self-compatible but are pollinator-dependent.These three orchid species offer nectar as a reward to pollinatorsand flower visitors. The twoAspidogyne spp. have a dorsally-adhesiveviscidium, a feature which precludes pollinators other thanbees. Erythrodes arietina flowers are protandrous and show aventrally-adhesive viscidium. Aspidogyne argentea is visitedby halictid bees (here ranked as probable pollinators) and Hesperiidaebutterflies. Aspidogyne longicornu is pollinated by femalesof Euglossa(Euglossini) and visited by the hummingbird Phaethornisruber and by the euglossine bees Eulaema seabrai(females) andEulaema cingulata(males). The pollinarium adheres to the ventralsurface of the bee labrum, a very difficult place for bees toclean. The dorsally adhesive viscidium in Aspidogyne parallelsthat of the Spiranthinae genera of the so-called ‘Pelexiaalliance’. This condition seems to be particularly adaptativeunder conditions of low-frequency pollinator visits. Erythrodesarietina is pollinated by bees of the genera Paratetrapediaand Osiris which carry the pollinarium on the dorsal surfaceof their proboscis. Occasionally, these bees remove pollinariafrom their mouthparts using their forelegs. In general, in thespecies studied, a combination of both pollinator behaviourand morphological peculiarities promotes cross-pollination.Copyright 2001 Annals of Botany Company Orchids, Goodyerinae, Aspidogyne, Erythrodes, pollination, bees, hummingbirds, butterflies, morphology, viscidium, protandry