Effect of High-Pressure Gas Atmospheres and Anaesthetics on Chilling Injury of Plants

High pressures and anaesthetics were used to study chillinginjury in plants. Changes in membrane fluidity at low but nonfreezingtemperatures are thought to be involved in chilling injury-aphysiological disorder of many economically important plants,e.g. banana, cotton, cucumber, maize, rice, sorghum, and tomato.High-pressure helium and nitrogen atmospheres of 12 MPa increasedthe severity of chilling injury (i.e. rate of ion leakage) inexcised cucumber cotyledon discs, cucumber hypocotyl segmentsand tomato pericarp discs, and also increased the thresholdtemperature at which chilling occurred by 2° to 6°C.Exposure to vapours of the anaesthetics halothane and methoxyfluranereduced chilling injury in cucumber cotyledon discs, cucumberhypocotyl segments and tomato pericarp discs. The relative effectivenessof the two anaesthetics in reducing chilling injury was similarto their relative effectiveness in inducing anaesthesia in animalsand their relative lipid solubilities. The response of the tissuesto halothane and methoxyflurane, which increase membrane fluidity,and to high pressures, which reduce membrane fluidity, are consistentwith the hypothesis that cold-induced phase transition of membranescould be responsible for chilling injury. However, other cellularcomponents may also be affected, e.g. low temperatures, highpressures and anaesthetics can alter protein conformation, affection channels, depolymerize microtubules and cause the releaseof calcium from membrane lipids. Key words: Cucumber, Cucumis sativus, tomato, Lycopersicon esculentum, halothane, ion leakage, methoxyflurane     

THE DIET AND PREY CAPTURE MECHANISM OF MELO MELO (PROSOBRANCHIA: VOLUTIDAE)

Laboratory experiments undertaken with the South China Sea volute,Melo melo, have shown that it is a specialized predator of othercontinental shelf predatory gastropods, notably Hemifusus tuba(Melongenidae) and Babylonia lutosa (Buccinidae). (Received 30 December 1985;     

THE IMPORTANCE OF MUCUS AS A DEFENCE AGAINST CARABID BEETLES BY THE SLUGS ARION FASCIATUS AND DEROCERAS RETICULATUM

The effect of mucus exudation on the survival of Arion fasciatusand Deroceras reticulatum was studied by exposing mechanicallystimulated and control slugs to Carabidae beetles for 24 hours.A light stimulation, lasting three minutes, exhausted the copiousflow of mucus for one day. A generalist, Pterostichus niger,significantly preferred stressed D. reticulatum over controlones. Similarly, P. niger exclusively ate stressed individualsof A. fasciatus. Two beetles which specialize in gastropods,Cychrus caraboides and Carabus violaceus, consumed an equalnumber of stressed and control D. reticulatum and A. fasciatus.The susceptibility of the slug species to predation was different:for each beetle species, the proportion of available D. reticulatumpreyed upon was significantly higher than that of A. fasciatus.The differences in the behaviour of A. fasciatus and D. reticulatumin defending themselves against attacks is described. The mainreason why specialist beetles are able to hunt slugs successfullyis their ability to prevent the slugs from exuding large amountsof mucus. This may succeed by different means: C. violaceustargeted their killing strokes against the posterior part ofthe mantle while C. caraboides hit the head of the slug. Inboth case the strokes seemed to paralyze the slugs. (Received 31 March 1993; accepted 1 October 1993)     

Suppression of the Defence-Related Oxidative Burst in Bean Leaf Tissue and Bean Suspension Cells by the Necrotrophic Pathogen Botrytis cinerea

The interaction of two selected isolates of Botrytis cinerea with bean suspension cells and bean leaf discs was compared in relation to levels of reactive oxygen intermediates (ROI). Isolate B 1.7 was arrested by a hypersensitive‐like necrosis of bean leaf tissue. According to its inability to spread and produce conidia on the bean leaf tissue it was classified as non‐aggressive. The second isolate induced a fast expanding light brownish necrosis of the leaf tissue. It was able to produce conidia on bean leaf discs and was classified as aggressive. The generation of superoxide was followed biochemically in inoculated bean cell suspensions. Both isolates induced a similar early superoxide peak approximately 18‐h post inoculation (hpi). While the non‐aggressive isolate induced a much stronger secondary superoxide burst at 33 hpi, the level of superoxide of suspension cells inoculated with the aggressive isolate was below the control level. This is the first report on the occurrence of a biphasic oxidative burst in plant cells induced by a fungal pathogen. Such a suppression of superoxide generation was also observed in bean leaf discs inoculated with the aggressive isolate. An oxidative burst‐suppressing agent was extracted from inoculated cell culture medium and determined as 2‐methyl‐succinate (2‐MS) by GC/MS analysis. The compound was detected approximately 20 hpi in the aggressive fungus–plant interaction. 2‐MS was able to suppress the hypersensitive response‐like necrosis on leaf discs as well as the second superoxide burst in suspension cells when inoculated with the non‐aggressive isolate. The early superoxide burst at 18 hpi was not affected. The results confirm the important role of enhanced production of ROI in plant resistance reactions, also for a necrotrophlike B. cinerea.     

DOES TANDONIA BUDAPESTENIS (MOLLUSCA: PULMONATA) CONTAIN TOXINS? EVIDENCE FROM FEEDING TRIALS WITH THE SLUG PREDATOR PTEROSTICHUS MELANARIUS (COLEOPTERA: CARABIDAE)

Slugs are known to be killed and consumed by a range of invertebrateand vertebrate predators in the field. Carabid beetles (Coleoptera:Carabidae) in particular are major natural enemies of slugs,and have been shown to be capable of controlling certain speciesin a crop environment. This paper reports experiments to investigatethe effects, on the carabid Pterostichus melanarius, of feedingon the milacid slug Tandonia budapestensis. The slugs provedto be toxic, 50% of the beetles dying within two days. Mortalityof beetles fed on two other species of slug, Deroceras reticulatumand Arion distinctus, was not significantly different from thatfor beetles fed upon a control prey (Calliphora vomitoria).These results represent the only known case of a European slugproving to be toxic to potential predators, and is one of avery small number of reported instances of possible toxicityamongst terrestrial gastropods. The possibility that the orangeline down the dorsal keel of T. budapestensis may act as warningcoloration to birds is discussed. (Received 4 December 1996; accepted 5 March 1997)     

Convection in ice-covered lakes: effects on algal suspension

Convection occurs in ice-covered lakes if solar radiation warmsnear-surface water from the freezing point towards the temperatureof maximal density. One effect of convective mixing may be tosuspend non-motile phytoplankton in the upper water column,providing cells with enough light for growth during ice-coveredperiods. Observations of the diatom Aulacoseira baicalensisunder the ice cover of Lake Baikal, Siberia, support the hypothesisthat convective mixing causes net suspension of cells. Thispaper presents a theoretical examination of the conditions underwhich convective flow fields can suspend algae in the photiczone of the upper water column. It is shown that the efficiencyof algal suspension depends on the ratio of the still-wateralgal sinking rate, W_p, to convective updraft speed, W_u. Thesuspension efficiency is also shown to be affected by asymmetriesin the flow field and night-time cessation of convection, butonly if W_p and W_u are comparable in value. It is concluded thatconvection in Lake Baikal should be vigorous enough to increasethe mixed-layer residence time of A.baicalensis from a few daysto over a month, at least during years with thin snow cover.     

COCCULINIFORM LIMPETS (COCCULINIDAE AND PYROPELTIDAE) LIVING ON WHALE BONE IN THE DEEP SEA OFF CALIFORNIA

Cocculiniform limpets of the families Cocculinidae and Pyropeltidaeare here reported for the first time on whale bone in the deepsea. The new species and records of previously described speciesare from four whale-falls at bathyal depths on the continentalmargin off California, from Monterey Bay to the Catalina Basin.The family Cocculinidae is represented by the new species Cocculinacraigsmithi. With few exceptions, the previously known speciesof Cocculinidae are known from wood substrates. The family Pyropeltidaeis represented by three species: Pyropelta musaica McLean &Haszprunar, 1987, originally described from the Juan de Fucahydrothermal vents, Pyropelta corymba McLean & Haszprunar,1987, originally described from the hydrothermal vent habitatat the Guaymas Basin, and one new species, P. wakefieldi. Thetwo previously known species of Pyropelta have heretofore beenregarded as obligate members of the sulfide habitat of hydrothermalvents. Pyropelta species are the first gastropods known fromboth habitats. Like the hydrothermal-vent habitat, the newlyreported habitat on whale bone is also a sulfide-rich, reducingenvironment. (Received 20 January 1991; accepted 28 April 1992)     

Role of pulvinar chloroplasts in light-driven leaf movements of the trifoliate leaf of bean (Phaseolus vulgaris L.)

Laminar pulvini of bean (Phaseolus vulgaris L.) contain numerouschloroplasts in cells of their motor tissue. The quantitativerelationships of the chloroplast pigments, chlorophyll a andb, ß-carotene, lutein, neoxanthin as well as the xanthophyllcycle carotenoids (violaxanthin, antheraxanthin and zeaxanthin)were similar to those of mesophyll chloroplasts from leafletlaminae. Exposure of pulvinules to light caused deepoxidationof violaxanthin to zeaxanthin, showing that the xanthophyllcycle is functioning. Chlorophyll fluorescence analysis of pulvinulesconfirmed that their chloroplasts are capable of both photosyntheticelectron transport and non-photochemical fluorescence quenching,showing that they build up a considerable transthylakoid protongradient in the light. Application of DCMU to excised pulvinulesand laminar discs, as well as to pulvinules of intact, attachedterminal leaflets blocked electron transport and fluorescencequenching. Application of the uncoupler CCCP to intact pulvinulesalso prevented non-photochemical fluorescence quenching. Therate of movement of the low-light-adapted terminal leaflet inresponse to exposure of its pulvinule to overhead red light(500 µmol m^–2 s^–1) was reduced when the pulvinulewas pretreated with DCMU. The pulvinar response to overheadblue light (50 µmol ^–2 s^–1), which is morepronounced than to red light, was not affected by similar pretreatmentwith DCMU. Pretreatment with CCCP caused a short lag in theresponse to red light, but did not affect its subsequent rate.The results suggest that the pulvinar response to red, but notto blue light, requires non-cyclic electron transport and theresulting generation of ATP Key words: Leaf movements, light, non-cyclic electron transport, Phaseolus, pulvinar chloroplasts     

Chemical Patterns, Compartments and a Binary Epigenetic Code in Drosophila

I propose a model which accounts for the geometries and sequencein which compartmental boundary lines arise on the differentimaginal discs, and on the blastoderm of Drosophila melanogaster;and propose that successive lines are recorded by differentbinary switches, to create a binary epigenetic code word specifyingeach disc, and disc compartment. I suppose a biochemical systemundergoing reaction and diffusion acts throughout development.As an imaginal disc grows, a succession of differently shapedchemical concentration patterns form at a discrete set of discsizes. I suppose a specific concentration of one chemical isa threshold. Concentrations above or below threshold switchcells to one or another of two commitments. Then the line acrossthe imaginal disc with the threshold concentration is a predictedcompartmental boundary. The sequence and geometries of suchlines predict the compartmental boundaries seen on the wingdisc, the other discs, and on the blastoderm stage egg. Thecompartmental lines on the wing disc suggest that a terminalcompartment is specified by a combination of binary names recordinga sequence of binary commitments: anterior, not posterior; dorsal,not ventral; wing, not thorax; proximal, not distal. Each combinationcomprises a binary epigenetic code word. Recently I constructedan independent model for transdetermination in Drosophila whichproposed a similar binary epigenetic code for the differentdiscs. The clone restriction lines predicted on the blastodermby my transdetermination model, the chemical pattern model,and analogy with the wing disc, are nearly identical. Severalare already confirmed. The resultant binary code scheme correctlypredicts many relative transdetermination frequencies and accountssimply for the action of most homeotic mutants as genes whichalter a single switch state in one or more discs.     

Physiological Basis for a Cycloheximide-induced Soft Rot of Potatoes by Pseudomonas fluorescens

Cycloheximide renders discs of potato tissue (Solanum tuberosum,cultivar Kennebec) susceptible to soft rot by a non-pathogenicisolate of Pseudomonas fluorescens. Pectate lyases (E.C. 4.2.99.3 [EC] )are the dominant extracellular macerating agents produced bythe test organism. Potato discs aged 24 h become resistant tomaceration by purified lyase preparations. Cycloheximide blocksthe development of resistance by inhibiting suberization. Thesite of inhibition is thought to be the cycloheximide-sensitivesynthesis of phenylalanine ammonia-lyase (E.C. 4.3.1.5 [EC] ) in potatodiscs. This enzyme is necessary for production of phenolic precursorsof suberin. Comparison of tissue from a number of potato cultivarscorrelates the synthesis of phenylalanine ammonia-lyase withresistance of discs to attack by the Pseudomonad. Resistance of potato tissue to pectate lyase is also affectedby intrinsic reactions not involving suberization. Resistanceincreases in fresh unsuberized discs when tubers are transferredfrom cold storage to room temperature before use. Resistancedecreases rapidly when tubers are transferred back to the cold.The intrinsic resistance appears to increase in the surfacelayer of cells in ageing discs. It is estimated that intrinsicreactions and suberization contribute equally to resistanceof aged discs to pectate lyase maceration.     

In vitro Regeneration from Excised Leaf Discs of Three Brassica Species

Excised leaf discs of three Brassica species, B. oleracea, B.napus, and B. campestris were induced to produce adventitiousbuds and subsequently entire plants by culture on media withspecific combinations of 6-benzylaminopurine (BAP) and -naphthylaceticacid (NAA). Each species required a particular hormone concentrationfor optimum growth and differentiation: B. oleracea, BAP 10mg^–1 and NAA 1 mg 1^–1; B. napus, BAP 10 mg 1^–1and NAA 10 mg 1^–1; B. campestris, BAP 1 mg 1^–1 andNAA 10 mg 1^–1. In a more detailed study on one of these species, namely B.oleracea, the relative influence of other media components suchas amino acids and other organic additives was examined. Itwas also found that the source and size of the explant greatlyaffected the growth response, as did the size of the culturevessel. The regenerated plants dislayed a range of ploidy as well asphenotypic abnormalities. Findings are discussed in relation to results from other tissueculture systems.     

THE MORPHOLOGICAL EXPRESSION OF IMPOSEX IN NUCELLA LAPILLUS (LINNAEUS) (GASTROPODA: MURICIDAE)

The prosobranch gastropod Nucella lapillus exhibits imposex(occurrence of male parts in addition to the female genitalduct) in response to tributyltin (TBT) pollution. Six stageswith three different types in the first three stages and twotypes in the last two stages can be distinguished and are documentedwith SEM-photographs for the first time. Furthermore, nine additionalalterations to the genital tract are shown. As a consequence of TBT exposure in early life stages a sexchange might occur. The oogenesis is suppressed and supplantedby spermatogenesis. The results are two observed specimens witha male genital tract (with a testis) and different female parts.Anatomical and histological details are given here. If TBT-expositionoccurs later, the vagina is replaced by a small prostate glandor the vaginal opening is occluded by proliferating tissue. The two established indices for PSH monitoring (VDS and RPS)in muricid gastropods are discussed. It is shown that the VDSis the more valid parameter. (Received 2 January 1991; accepted 1 March 1991)     

Direct and indirect cues of predation risk influence behavior and reproduction of prey: a case for acarine interactions

Little is known about the flow of chemical information fromhigher to lower levels within the animal food chain. However,this information may determine the behavior and distributionof many animals (e.g., that of potential prey) when exposedto direct and indirect cues of predation risk. We used herbivorousspider mites, Tetranychus urticae Koch (Tetranychidae) as amodel to examine the foraging and oviposition decisions thatprey make when exposed to these cues. We conducted laboratorytests to determine if the previous presence of predators (directcues) on leaf discs or the presence of injured conspecifics(indirect cues) alters the distribution of adults and eggs ofT. urticae. When given a choice, after 24 h, fewer adults and eggswere found on leaf discs that had previously contained specialistspider mite predators, Phytoseiulus persimilis Athias-Henriot (Phytoseiidae),than on discs unexposed to predators. Also, more T. urticaeemigrated from predator-exposed discs than from unexposed discs orfrom those that had previously contained nonpredatory mites(Tyrophagus putrescentiae, Acaridae). Finally, fewer T. urticaeforaged and laid eggs on predator-exposed discs or on thosewith artificially damaged conspecifics (eggs or dead adults)than on discs with intact conspecifics. Tetranychus urticaeprobably recognizes infochemicals (kairomones) from its predatorsor cues from injured spider mites and consequently avoids feedingor ovipositing in areas exposed to these cues. Recognition and avoidanceof kairomones from specialist predators by this prey are likelyto be hereditary, but avoidance of injured conspecifics maybe an adaptation to avoid predators that are not inherentlyrecognized. We discuss the behavioral and ecological implicationsof our findings.     

Cell-Wall Changes in Potato Tuber Tissue 4Phytophthora infestans (Mont.) De Bary

Examination of the carbohydrates of cell walls prepared fromtuber discs of a susceptible variety of potato showed an increase,with time, in all the polysaccharide fractions in control discs,but a slower increase in the pectic fraction and a more rapidincrease in the extraction residue to discs infected with Phytophthorainfestans. These differences were related to the monosaccharidecomposition of hydrolysates; there was no increase in galactose,found predominantly in the pectic fraction, but a rapid increasein glucose which is confined almost exclusively to the extractionresidue. Part of the increased glucose was due to an accumulationof hyphal wall of P. infestans which contains mainly an alkali-insolubleglucan. Galactanase activity, which was demonstrated in infecteddiscs, could account for the divergence of galactose contentfrom that of the controls. There was an enhanced accumulationof a lignin-like polymer associated with the cell-wall fractionof infected discs.     

Ineffectiveness of cytokinin-induced chlorophyll retention in hypostomatous leaf discs

Kinetin retarded the decrease in chlorophyll content in leafdiscs from 5 species of plants with amphistomatous leaves, wherethe upper surface was exposed to air, but not in Rumex acetosera.When leaf discs were floated so that the lower surface was exposed,the effect of kinetin was less evident. Kinetin also stimulatedtranspiration in leaf discs from Nicotiana tabacum (amphistomatous),but not in leaf discs from Paederia chinensis (hypostomatous).Nor kinetin did retard chlorophyll breakdown in this specieswhen leaf discs were floated so that the stomatal surface wasin contact with the solution. The ineffectiveness of cytokininsin chlorophyll retention in leaf discs from hypostomatous leaveswas not due to reduced uptake of benzylaminopurine-¹⁴C. Chlorophyll retention was severely inhibited by coating theleaf surface with vaseline either in the presence or absenceof kinetin. Leaf discs floated on a solution exposed to CO₂-lessair retained more chlorophyll than those in normal air. Thereis thus a close relationship between stomatal opening (as measuredby stimulation of transpiration) and chlorophyll retention,as influenced by cytokinins. It is suggested that cytokinin-induced chlorophyll retentionand odier effects on leaf tissues could be mediated throughits effects on stomatal opening. (Received January 22, 1976; )     

The Influence of Leaf Water Status and ABA on Leaf Growth and Stomata of Phaseolus Seedlings with Hypoxic Roots

The objective of this study was to assess the relative rolesof leaf water status and root-sourced signals in mediating beanleaf responses to root hypoxia. To do so, the roots of beanplants under varied VPD (0.95 kPa to 0.25 KPa) were made hypoxic.Under all conditions, leaf growth rates and stomatal conductanceswere reduced. There was a transitory decline in leaf water potentialat high VPD which accounted for the initial reduction in leafgrowth rates and stomatal conductance. At low VPD, no waterdeficits were detected. Leaf growth inhibition and reduced stomatalconductance under low VPD treatments were unrelated to leafwater status and must be induced by some other factor. In vitrogrowth of leaf discs was reduced by xylem sap collected fromhypoxic roots. Exogenously applied ABA, at high concentrationsin KCl and sucrose, or at low concentrations diluted in xylemsap from aerated plants, inhibited in vitro growth of leaf discs.Applications of ABA in the transpiration stream reduced stomatalconductance.     

MORPHOLOGY OF THE MATURE SPERMATOZOON OF PHYSA ACUTA (DRAPARNAUD, 1801) (GASTROPODA: PHYSIDAE)

The morphology of the spermatozoon of Physa acuta (Draparnaud,1801) was examined using TEM. It was found to be of the modified-type,sharing characteristic features of other basommatophoran species.However, differences were noted in some cases, for example,in P. acuta the nucleus was torpedo-shaped with two helicalkeels, the midpiece possessed a maximum of three glycogen helices,the end piece was long and tapered and the total length of thespermatozoon was 365 µm. No identical spermatozoa havebeen found in other basommatophoran gastropods studied so far.If spermatozoon morphology is unique for individual specieswithin the genus Physa, it may provide a useful taxonomic toolin helping to clarify the uncertainty that surrounds the systematicsof this genus. (Received 26 February 1990; accepted 28 June 1990)     

Across-shelf transport of gastropod larvae in the central Bahamas: rapid responses to local wind conditions

Surveys for veliger larvae of the large gastropods Strombusgigas and Strombus costatus were carried out in duplicate transectsrunning offshore (0.26–5 km) from Lee Stocking Island,Exuma Cays, Bahamas. The across-shelf distribution of the larvaeduring the 1991 spawning season was highly variable over periodsof 3–6 days. Larvae of both species are known to inhabitthe upper few meters of the water column, and analysis of windstress patterns over the study period showed that across-shelfdistribution of the larvae was affected by wind forcing. Seaward(recruitment-unfavorable) transport near Lee Stocking Islandwas most highly correlated with wind stress toward the north-northwest(335–357). The resultant wind stress during the studywas toward 279, suggesting that recruitment of conch to nurserygrounds on the Great Bahama Bank in the Exuma Cays occurs underanomalous summer wind conditions. The correlation between theacross-shelf distribution of conch veligers and wind stresswas highest with extinction coefficients of 0.17–0.23in the exponentially filtered wind stress. This indicates thatlarval distribution over the 5-km-long transects responded rapidlyto changes in wind stress. Over 75% of the effective wind stressoccurred over just 6–8 h preceding collections; therefore,short-term changes in wind stress, such as afternoon strengtheningof the trade winds, may have a significant influence on across-shelflarval transport. ³Present address: Northeast Fisheries Science Center, NationalMarine Fisheries Service NOAA, 74 Magruder Road, Highlands,NJ 07732, USA     

A snail's space sets a snail's pace: movement rates of lavigeria gastropods in lake tanganyika, East africa

Endemic Lavigeria gastropods are diverse and common in the benthosof Lake Tanganyika. We used in situ studies of marked individualsto quantify rates of daily movement by three species, and testthe effects of size, sex, reproductive status and parasitismon movement. Average net travel distance was 50 cm day^–1,which corresponds to about 20 times shell length. Male L. coronatamoved significantly farther than L. coronata females or L. grandis,and L. nassa of either sex. There were also significant differencesamong individuals within each group; however, these differenceswere not predicted by size, reproductive status or parasitism.We interpret greater movement of L. coronata males as a reflectionof mate searching; the ratio of males to non-brooding, non-parasitizedfemales was three times as high in L. coronata (21:1) as inthe other species (6:1). Our results indicate that these snailsare capable of moving considerable distances, and that the highlylocalized distribution of L. coronata populations is not simplya reflection of limited movement by individual snails. (Received 20 September 2006; accepted 1 March 2007)     

EFFECT OF AMINO ACID IMBALANCE IN ARTIFICIAL DIETS ON FOOD CHOICE AND FEEDING RATES IN TWO SPECIES OF TERRESTRIAL SNAILS, CEPAEA NEMORALIS AND ACHATINA FULICA

Postingestive response to dietary imbalance of amino acids wasstudied in two species of terrestrial pulmonate gastropods Cepaeanemoralis and Achatina fulica using agar-based chemical diets.Both species showed preference responses to an experimentaldiet complete in all nutrients, and aversive responses to experimentaldiets containing excesses of methionine (in concentrations 1-10%dry wt of diet). Aversion to methionine was stronger in Achatinathan in Cepaea. One day's experience on a particular diet didnot significantly affect an animal's subsequent feeding responseon the same or different diets. What appeared to be more importantin influencing food choice in both species was day-to-day contactwith a given diet. (Received 7 March 1988; accepted 4 May 1988)