AGR,an Agravitropic Locus of Arabidopsis thaliana, Encodes a Novel Membrane-Protein Family Member

Mutations in the Agr locus of Arabidopsis thaliana impair theroot gravitropic response. Root growth of agr mutants is moderatelyresistant to ethylene and to an auxin transport inhibitor. Verticallyplaced agr roots grow into agar medium containing IAA or naphthalene-1-aceticacid, but not into medium containing 2,4-D. Positional cloningshowed that AGR encodes a root-specific member of a novel membrane-proteinfamily with limited homology to bacterial transporters. (Received September 4, 1998; Accepted September 21, 1998)     

RECRUITMENT AND GROWTH OF THE BLUE-RAYED LIMPET, HELCION PELLUCIDUM (L.), IN SOUTH EAST IRELAND

This account reports on recruitment, growth and population structureof the macroherbivorous gastropod Helcion pellucidum (L.) onan exposed rocky shore in S.E. Ireland, with particular referenceto the pellucidum form. Recently settled Helcion spat were foundinitially on living crustose lithothamnia in pools and on openrock, on the lower shore, during February-April and subsequentlyrecruited to macro-algal fronds. By May they were found in abundanceon Mastocarpus stellatus and Laminaria spp. Helcion was markedlyseasonal in its occurrence on Mastocarpus, being most abundantduring May-August. A complementary pattern was evident on growingHimanthalia receptacles, with limpets abundant from July onwards.It is suggested that Helcion may migrate from Mastocarpus toHimanthalia as they grow. Data on growth rates are presentedfor Helcion in the various habitats studied. Growth rates werehighest on the Laminaria spp. (Received 21 February 1992; accepted 8 June 1992)     

Contrasting life histories of the predatory cladocerans Leptodora kindtii and Bythotrephes longimanus

The predatory cladocerans, Leptodora kindtii (Focke, 1844) andBythotrephes longimanus (Leydig, 1860), express markedly differentlife-history traits. Leptodora produce small-bodied neonatesthat mature at small sizes but continue to grow throughout life.Bythotrephes produce larger neonates in both relative and absoluteterms that grow rapidly to a large size at maturity whereuponthey curtail somatic growth and divert resources mainly to reproduction.Despite their remarkable differences, the sets of life-historytraits of both species appear to be solutions to the same basicselection pressures imposed by visually discriminating gape-limitedfishes and foraging constraints imposed by prey size. Leptodorastresses pre-contact (transparency) while Bythotrephes stressespostcontact (caudal spine) modes of morphological defense againstfishes. Mounting these disparate modes of defense has consequencesfor selection on timing and allocation to body growth that mayunderlie competitive imbalance between the species. Owing tothe production of large-bodied neonates that grow rapidly, Bythotrephesquickly attain body sizes that both admit them to a broaderprey base in size and taxonomic variety, and allow shorter preyhandling times, in comparison to Leptodora. This provides Bythotrepheswith a wider and more exploitable prey base from an earlierage and may explain why Leptodora has declined in density followingBythotrephes invasion into some North American lakes. The divergentsets of life-history traits expressed by Leptodora and Bythotrephesparallel two dominant life-history strategies evolved by phytoplanktivorousspecies of the order Cladocera.     

Nutrient Supply, Dry-matter Production and Nutrient Uptake of Forest Tree Seedlings

The dry-matter production and nutrient uptake of forest-treeseedlings grown under controlled levels of nutrition in sub-irrigatedsand culture were investigated. Hardwood seedlings attainedgreater dry weight than conifer seedlings, and Pinus radiataa greater dry weight than P. contorta and P. nigra, but thesegreater dry weights were not related to greater leaf/weightratios, although seed size may have been an important influenceon final seedling dry weight. P. radiata was found to have alower requirement for P than P. contorta and P. nigra in oneexperiment. The demand (total nutrient uptake per unit of time) made bythree species for nutrients upon a site was shown to dependmore upon growth-rate per annum than on efficiency (quantityof nutrients required to produce a unit of dry matter). It isconcluded that the ability of tree species to grow satisfactorilyon soils of low nutrient status depends largely on their abilityfor relatively slow growth. On the other hand, species showinggood response to favourable sites may also make satisfactorygrowth on poor sites.     

Production of a Fungistat and the Role of Fungi during Germination of Digitalis purpurea L.cv. Gloxiniaflora Seeds

The seed coats of Digitalis purpurea L. cv. Gloxiniaflora werecultured for indigenous fungi. Alternaria alternata (Fries)was identified as the sole fungus on seeds freshly harvestedfrom unopened capsules, whereas A. alternata, Rhizopus arrhizus(Fischer), Penicillium sp. and other fungi appeared on storedseeds. The appearance of fungi in seed cultures was seasonal,being more frequent in winter and early spring than in summerand autumn. Alternaria grew well on autoclaved seeds, on dehiscentseed coats, or on seed coats separated from the embryos of ungerminatedseeds. Rhizopus did not grow on these but grew weakly on theculture medium from viable seeds. A. alternata appears to functionas a degradation agent for the seed coat subsequent to germination.Neither fungus was found to be essential to germination of Digitalisseeds. Bioassay of the culture medium from germinating seedsshowed that a fungistat effective against both Alternaria andRhizopus is produced coincident with germination. Based on chromatographicanalysis, the fungistat appears to be a cardenolide. Alternaria alternata (Fries), cardenolides, Digitalis purpurea L. cv, Gloxiniaflora, fungistats, germination, Rhizopus arrhizus (Fischer)     

Life table responses and population dynamics of four cladoceran zooplankton during a reservoir flood

The life table responses and population dynamics of four cladocerans(Ceriodaphnia lacustris, Daphnia parvula, Diaphonosoma leuchtenbergianumand Moina micrura) were measured during a flood of a large turbidreservoir (Lake Texoma, Oklahoma-Texas). Mean recruitment andlongevity of Ceriodaphnia and Daphnia in life table experimentswere reduced during the flood when abundant silt particles andpicoplankton (<2 µm) replaced algal particles in thewater column. Individual growth rates measured in the life tableexperiments were slower for Ceriodaphnia during the flood. Fieldcollections revealed that Ceriodaphnia and Daphnia populationsdeclined immediately after the arrival of turbid water, andremaining females carried fewer eggs. Populations of Moina andDiaphanosoma increased during the flood, and life table experimentsshowed that these species were able to grow well in silt-ladenwater.     

Borers in the Shell of the Sea Scallop, Placopecten magellnnicus

Shells of the sea scallop, Placopecten magellanictis Gmelinfrom Newfoundland waters were examined for borers by directstereomicroscopic and X-ray radio-graphic means. Young shells are first attacked by the boring sponge, Clionavastifica, and the spionid polychaetes, Polydora websteri andPolydora concharum. The former settles almost exclusively onthe lower valve, but as it grows it often spreads to the uppervalve via the hinge region. The spionids settle on the uppervalve or occasionally on the periphery of the lower valve. Older shells are bored by the cirratulid polychaete, Dodecaceriaconcharum, which usually settles in empty Polydora burrows andenlarges them as they grow. The bivalve, Hiatella arctica, settlesin Cliona holes. The burrows formed by the borers can be recognized on the radiographs.However, the identity of the present inhabitant cannot be predictedwith accuracy because the original borer is often replaced bynestlers. The rale of growth was documented by making sequential radiographsat monthly intervals from May to October 1968. Rate of growthin all forms appears to be temperature-dependent. The watertemperature increased from 1°C in May up to 18°C inAugust. Polydora concharum and P. websteri grew more rapidlyfrom July to October than in Mayand June, while Cliona and Dodecaceriaonly grew during the months of July to October.     

Sulfur requirement of Gonium (Volvocaceae)

The sulfur requirement of six strains of three species of Goniumhas been investigated. These strains can grow well with sulfide,sulfite, bisulfite, thiosulfate or sulfate in light and darkness.They are the first algae shown to utilize sulfide as a sulfursource. However, organic sulfur sources (methionine, cystine,cysteine, homocysteine, homocystine and taurine) were ineffectivefor growth of Gonium. (Received December 6, 1975; )     

The influence of autotrophic and heterotrophic foods on the demography of Daphnia longispina under starved, semi-natural and enriched conditions

We tested the influence of different types of food on the fitnessof Daphnia longispina during a period of poor resources by comparingthe growth and reproduction of individuals fed on differentdiets. When Daphnia were under starvation conditions, both dissolvedorganic carbon and metabolic products enhanced bacterial growth,and the cladoceran produced 15 neonates and survived for the55 days of experiment. In the natural water, the edible foodconsisted essentially of bacteria and heterotrophic flagellates,which enabled the cladoceran to grow and reproduce. In waterenriched with Cryptomonas (an alga) or Chilomonas (a heterotrophicflagellate), the daphnid growth rates increased considerablyfrom generation to generation, but later in the time courseof the experiment with Chilomonas than with Cryptomonas. Thisalga enhanced the phosphorus:carbon ratio. The primiparous daphnidsfed with Cryptomonas were smaller than those fed with the heterotrophicflagellate and enrichment with the heterotrophic flagellatealso enhanced reproduction. In Lake Tazenat, when the algalbiomass was insufficient to support the Daphnia life cycle,the heterotrophic organisms were an essential food source. Whenfeeding essentially on bacteria, Daphnia has the capacity togrow and reproduce at very low food concentrations, and thisis important in determining its fitness under competitive conditions.     

Newly Isolated Mutants of Neurospora crassa That Can Grow Optimally in a Low-Calcium Medium

Two mutants of Neurospora crassa that grow well in a mediumin which the concentration of calcium ions is lower than thatin the medium used for the culture of the wild-type strain havebeen isolated. One mutant strain, ca-101, must be allelic ortightly linked to co-1(19) which was isolated previously. Recombinationfrequencies for ca-1 and cys-9 and for ca-1 and un-1 in linkagegroup I were about 10%, in each case. The other strain, ca-3(105),carried a mutation in another gene, ca-3, which appeared tobe closely linked to ca-1 since the frequency of recombinationbetween these two genes was about 5%. All strains were comparedin terms of period length and phase of the circadian conidiationrhythm with the wild-type strain. One of the mutants, ca-101,had a shorter period length than that of the wild-type strain. (Received June 19, 1992; Accepted November 24, 1992)     

Observations on the Biology of Fomes annosus, with Particular Reference to East Anglian Pine Plantations: II. Spore Production, Stump Infection, and Saprophytic Activity in Stumps

F. annosus produces conidia abundantly in culture but rarelyunder natural conditions. Sporophorea are formed on stumps anddying trees throughout the year provided that the humidity issufficiently high. Spore discharge in the plantations may occurat any time of year, but slowa down or ceases during very dryweather. It takes place at low temperatures, ceasing only whensporophores freeze. In the laboratory, F. annosus basidiospores germinate in relativehumidity exceeding 92 per cent. on freshly cut, unsterilizedpine wood. Viability is lost rapidly in light at temperaturesabove 15°C. Under humid conditions F. annosus spores will infect freshlycut pine stumps. There is evidence that spores of F. annosus washed down intosoil remain viable for at least a short period and that stumpscovered with soil are infected from this source. F. annosusspores can infect stumps for only a few weeks after felling,colonization after a longer interval probably beingprevdntedby competing fungi. In stumps inoculated with a mixed suspensionof F. annosus and Peniophora gigantea spores, Fomes at firstcolonized the wood but was soon replaced by P. gigantea. Otheraspects of competition are discussed. The incidence of natural infection in stumps and the factorsaffecting it are discussed Growth rates of F. annosus on malt agar and in lengths of pineroot are given. The fungus grows in stump roots at about 1 m.per year, and so closely approaches adjacent trees within ayear of thinning the plantation: In large stumps, F. annosusmay survive 15 or even 30 years after felling. Data are givenwhich suggest that the infective capacity of stumps containingF. annosus is greater in alkaline than in acid mils, while replacementby other fungi is slower. Competition of F. annosus with other fungi during colonizationof stumps is discussed. The parasite can grow along roots alreadyoccupied by certain fungi but not along roots containing others.The probable course of succession in stumps rotted by F. annousis described.     

Sexual Dimorphism in Cirsium arvense (L.) Scop

Differences between males and females of Cirsium arvense (L.)Scop. in morphology and sexual performance are described. Nofunctional pollen was observed in females, and no pollen-sterileanthers were observed in males. The difference between the sexesin ovule functions is not absolute however: some males produceoccasional fruits. The number and distribution of fruits onboth sexes are described. The fruits borne on males are smallerand germinate less well than those borne on females, but theseedlings from the two sexes grow equally well. On the average,males contribute only 5.3 x 10^–4 as many genomes via ovulesas do females. The average male constancy, the proportion ofmale genes transmitted via pollen, is estimated as 0.9989. Theprimary sex index, a measure of the functional approach to strictdioecy (represented as 1.00) is 0.9995. C. arvense is describedas near-dioecious and varying from dioecy in a gynodioeciousmanner. The opinion expressed by Correns that the near-dioecyof C. arvense has been derived from hermaphroditism via gynodioecyis upheld.     

Pollen-pistil Interaction in a Non-pseudogamous Apomict,Commiphora wightii

Structural and cytochemical details of the pistil and the interactionof pollen and pistil were studied in a non-pseudogamous apomict,Commiphorawightii.The anthers in the male and bisexual flowers producefunctional pollen grains. The stigma is of the wet and papillatetype. The style is typically solid with two strands of transmittingtissue that traverse the entire length of the style. There isa marked reduction in the area occupied by the transmittingtissue from the stigma to the base of the style. The cells ofthe transmitting tissue are isodiametric in transverse as wellas longitudinal section and do not form longitudinal files ofelongated cells as reported for other taxa. Proteins could notbe localized in the intercellular matrix. Although pollen grainsgerminate on the stigma, pollen tubes do not grow beyond theproximal one third of the style. Changed orientation of thecells of the transmitting tissue and absence of proteins inthe intercellular matrix could account for the failure of thepistil to support pollen growth.Copyright 1998 Annals of BotanyCompany Guggul, pollen-pistil interaction, non-pseudogamous apomict,Commiphora wightii, transmitting tissue     

Haustorial Role of Pollen Tubes

In angiosperms, the pollen tube is siphonogamous and its mainfunction is to carry the male gametes for double fertilization.In some taxa, as in Cucurbitaceae, the tube branches after enteringthe ovule, prior to fertilization. The tube may even swell andform a bulla. During post-fertilization development of the ovule,a portion of the tube may persist in the micropyle, or in theembryo sac, or in both, sometimes even in the micropyle of themature seed. Haustorial function has been presumed in a numberof taxa. In Grevillea, following fertilization, the pollen tube branchesat the micropyle, and the branches grow intercellularly intothe ovarian tissue where further branching occurs. A haustorialrole of the pollen tube is presumed from circumstantial evidence.In gymnosperms (for example, Cycas, Zamia and Ginkgo) the pollentube is nonsiphonogamous, arises from the distal (upper) poleof pollen grain, and grows laterally in the apical region ofthe nucellus. The tube branches in Cycas and Ginkgo but remainsunbranched in Zamia. These pollen tube branches are enucleate,and are not concerned with the transport of male gametes forfertilization. However, the haustorial role has been well documented.In Podocarpus, the pollen tube is siphonogamous and arises fromthe proximal (lower) pole of pollen grain. After traversingthe nucellus, the tube forms a bulla at the point of contactwith the female gametophyte, and several branches originatefrom the bulla. The pollen tube branches grow along the innersurface of the nucellus and the outer surface of the femalegametophyte. The haustorial role of the pollen tube branchesis uncertain. Procedures for convincingly demonstrating thehaustorial role of pollen tubes are discussed. Angiosperms, gymnosperms, pollen tube, bulla, fertilization, haustorial role     

The Effect of Low Temperature upon Starch, Sucrose and Fructan Synthesis in Leaves

Measurements on plants in a temperature gradient tunnel showthat diurnal accumulation of starch in illuminated leaves wasgreatly reduced at temperatures below 8 °C, whereas sucrosesynthesis was less affected under similar conditions. High chillingsensitivity for leaf starch accumulation was observed in a numberof chilling resistant temperate species. Enzymes of sucroseand fructan metabolism from mature leaves of Lolium temulentumwere less strongly inhibited at low temperatures than enzymesinvolved in starch synthesis. These results are discussed inrelation to carbon partitioning in species which grow and aremetabolically active at chilling temperatures. Lolium temulentum, starch, sucrose, fructan, temperature, enzyme activity, carbon partitioning     

Effects of temperature and salinity on the growth of the red tide flagellates Heterocapsa circularisquama (Dinophyceae) and Chattonella verruculosa (Raphidophyceae)

Growth responses of the red tide flagellates, Heterocapsa circularisquama(Dinophyceae) and Chattonella verruculosa (Raphidophyceae),were examined with 36 different combinations of temperature(5–30°C) and salinity (10–35 PSU). Heterocapsacircularisquama did not grow at or below a temperature of 10°C.The maximum growth rate of H.circularisquama (1.3 divisionsday^–1) was obtained with a combination of 30°C and30 PSU. In contrast, C. verruculosa did not grow at 10 PSU andat temperatures of 25°C or more. The maximum growth rateof C. verruculosa (1.74 divisions day^–1) was obtainedwith a combination of 15°C and 25 PSU. A significant temperature-salinityinteraction on growth was found by factorial analysis. Basedon the physiological characteristics obtained in the presentstudy, these novel flagellates have a potential for future outbreaksof red tides in pre viously unaffected waters.     

Mutations in the SGR4, SGR5 and SGR6 Loci of Arabidopsis thaliana Alter the Shoot Gravitropism

Shoots of higher plants grow upward in response to gravity.To elucidate the molecular mechanism of this response, we haveisolated shoot gravitropism (sgr) mutants in Arabidopsis thaliana.In this report, we describe three novel mutants, sgr4-1, sgr5-1and sgr6-1 whose inflorescence stems showed abnormal gravitropicresponses as previously reported for sgr1, sgr2 and sgr3. Thesenew sgr mutations were recessive and occurred at three independentgenetic loci. The sgr4-1 mutant showed severe defect in gravitropismof both inflorescence stem and hypocotyl but were normal inroot gravitropism as were sgr1 and sgr2. The sgr5-1 and sgr6-1mutants showed reduced gravitropism only in inflorescence stemsbut normal in both hypocotyls and roots as sgr3. These resultssupport the hypothesis that some mechanisms of gravitropismare genetically different in these three organs in A. thaliana.In addition, these mutants showed normal phototropic responses,suggesting that SGR4, SGR5 and SGR6 genes are specifically involvedin gravity perception and/or gravity signal transduction forthe shoot gravitropic response. (Received November 21, 1996; Accepted February 17, 1997)     

Pollination and Pollen-pistil Interaction in Oil Palm, Elaeis guineensis

Structural and cytochemical aspects of the pistil and detailsof pollination and pollen-pistil interaction were investigatedin the African oil palm (Elaeis guineensis Jacq.), an importantperennial oil crop. The stigma is trilobed, wet and papillate.The branched papillae are confined to a narrow linear zone oneach stigmatic lobe. Each stigmatic lobe harbours a deep stigmaticgroove, which runs adaxially along the surface. The stigmaticgroove is bordered by a well-defined layer of glandular cells,each of which has a pectinaceous cap on the inner tangentialwall. The style is hollow. The canal cells show thickeningson the inner tangential wall. The stigmatic groove and stylarcanal contain an extracellular matrix secreted by the canalcells which is rich in proteins, acidic polysaccharides andpectins. The canal cells at the base of the style are papillateand loosely fill the stylar canal. The stigma becomes receptivewhen the stigmatic lobes separate, and remains so for 24 h.Pollination is mediated by weevils as well as by the wind. Undernatural conditions the pollination efficiency was 100%. Pollinationinduces additional secretion in the stigmatic groove and stylarcanal. During post-pollination secretion, the pectinaceous capsof the cells lining the stigmatic groove are degraded. Pollengrains germinate on the stigmatic papillae and tubes grow onthe surface of the papillae, entering the stigmatic groove andadvancing along it into the stylar canal to eventually gainaccess to the locules. Pollen tubes are seen in the ovules 18–20h after pollination. Copyright 2001 Annals of Botany Company Arecaceae, Elaeis guineensis, African oil palm, pollination, stigmatic grove, stylar canal, Tenera hybrid, weevil     

Ability of Phaeocystis sp. to grow on organic phosphates: direct measurement and prediction with the use of an inhibition constant

Batch culture experiments were performed to test the abilityof Phaeocystis sp. to grow on organic phosphates as the onlysource of phosphorus.Of nine organic phosphates tested sevensupported growth equally well as did inorganic phosphate Growthon cyclic-adenosine monophos-phate (c-AMP) was slow comparedwith inorganic phosphate, while myo-inositol hexaphosphate (phytin)was not used for growth by Phaeocystis. The relative affinityof Phaeocystis alkaline phosphatase for a number of organicphosphates, including those used in the growth tests, was determinedby measuring the ability of the organic phosphates to inhibitthe hydrolysis of a test substrate by the enzyme. The relativeaffinity was expressed by means of an inhibition constant (K₁)values for c-AMP and phytin were relatively high, indicatinglow affinity of the enzyme for these substrates K₁, values forthe other phosphates tested were much lower indicating highaffinity of the enzyme. Comparison of the results of the growthexperiments with the Kt values indicated that the latter weresuitable instruments for predicting the outcome of the growthexperiments The results imply that in natural environments Phaeocystiscan use enzyme-hydrolysable organic phosphates efficiently forgrowth.     

Isolation and Characterization of Temperature-Sensitive, High-CO2 Requiring Mutant of Anacystis nidulans R2

Temperature-sensitive (ts), high-CO₂ requiring mutants of Anacystisnidulans R2 were isolated by N-methyl-N'-nitro-N-nitrosoguanidine(MNNG) mutagenesis and ampicillin enrichment. One of these mutantswas able to grow under ordinary air enriched with 5% CO₂, butnot under ordinary air at 40?C. At 40?C, the concentration ofCO₂ at which the rate of oxygen evolution reached half the maximumvelocity (apparent Km(CO₂) in photosynthesis) was 1,000 timeshigher in mutant cells than in wild type cells, whereas therewas no significant difference in the maximum rate of photosynthesis. When wild type and mutant cells were incubated with 55 µmNaHC0₃ under illumination at 40?C, the initial rate of inorganiccarbon (IC) transport from the medium into the cells and themaximum internal IC accumulation were significantly higher inwild type cells than in mutant cells. These results indicate that the isolated high-CO₂ requiringmutant lacks the ability in transporting IC into the cells at40?C. Furthermore, the finding that the mutant cells which aredefective in IC transport cannot grow under ordinary air suggeststhe importance of IC concentrating system(s) in photosynthesisof cyanobacteria. Present address: Department of Molecular Biology, The Universityof Wyoming, Laramie, Wyoming 82071, U.S.A. To whom reprints should be requested. (Received April 28, 1988; Accepted September 14, 1988)