Contributions to the Morphology of Some Species of Microsorium

Morphology of eleven epiphytic and rupicaulous species of Microsoriumis described. The paleae in the genus are either peltate withthe basal region developing secondarily as a hood over the stalk,or basally attached with auricles on either side of the stalk.The auricles in M. hancockii and M. pteropus develop from singleinitial cells adjacent to the stalk, while in the others nospecialized initial cells occur. Marginal and terminal glandularhairs occur on the paleae, except in M. hancockii and M. pteropusin which marginal hairs are absent. Slender sclerenchyma strands are scattered profusely in theground tissue of the rhizome. The stelar cylinder is dictyostelicand is dissected by lacunae into cylindrical vascular bundles.Leaf traces are multiple strands originating as branches fromthe dorsal median vascular bundle of the stelar cylinder andthe one next to it on each side. Two or three closely placedvascular bundles of the rhizome constitute the vascular connexionto each branch of the rhizome. Venation of the leaf lamina is reticulate with most of the free-endingveinlets entering foliar hydathodes. The juvenile leaves bearhairs similar to the pro-thallial hairs and are spatulate witha medianly placed forked vein. Sori are generally punctiform,but in M. hancockii and M. pteropus spread slightly over theveins, often forming elongated coenosori. Uniseriate (multiseriatein M. rubidum), multicellular paraphyses occur in all speciesexcept M. scolopendria. The spores are monolete and either psilateor granulate. The prothalli develop from 3-5 cells long germ filaments inwhich the anterior cells divide longitudinally and form an ameristicprothallial plate. An apical meristematic cell is formed later,and a cordate prothallus is developed, except in M. hancockiiand M. pteropus in which a definite meristem is never formedand the prothalli are ribbon-shaped and branched. The cordateprothalli possess polypodiaceous hairs: the ribbon-shaped onesare more or less naked and devoid of any midrib. The chromosome number in the species is n = 36 (zn = 72).     

LYCOPODIUM PROTHALLI AND THEIR ENDOPHYTIC FUNGI AS STUDIED IN VITRO

Freeberg , John A. (Lehigh U., Bethlehem, Pa.) Lycopodium prothalli and their endophytic fungi as studied in vitro. Amer. Jour. Bot. 49(5): 530–535. Illus. 1962.—A fungus isolated from a prothallus of Lycopodium obscurum is described. This fungus was found to invade prothalli of L. complanatum, L. selago and L. cernuum. The association of the fungus with L. complanatum in vitro is such that the form of the prothallus as well as the general area of fungus invasion approaches that of prothalli in nature. Prothalli grown with the fungus on a starch medium were found to gain in weight more rapidly than prothalli grown alone. This suggests that the presumed symbiotic relationship in nature can be duplicated in vitro under certain conditions.     

Colchicine Effect and the Production of Abnormal Spermatozoids in the Prothalli of Dryopteris subpubescens (BI.) C.Chr. and Goniopteris prolifera Roxb

Dilute colchicine solutions have been found to modify the earlystages of germination of spores in the ferns Dryopteris subpubescensand Goniopteris prolifera. When subsequently grown on soil theprothalli continued to grow abnormally and produced abnormalsperms. Certain prothalli in both species produced large sperms,possibly being diploid, and others and less normal ones producedgiant possibly tetraploid sperms. Monstrous sperms were noted in which two, three, or four bodieswere all united in front, or more rarely where the body forksinto two heads.     

The Ecology of Armillaria mellea in Britain Biological Control

The first trial in Britain of a method developed and used inEast Africa to control Armillaria mellea is described. Contraryto experience in East Africa, colonization of hardwood rootsby A. mellea was not reduced either by ringbarking trees beforefelling, or by frill-girdling and poisoning. Five years afterfelling, roots of trees treated in this manner were found tobe fully colonized, while invasion of the roots of untreatedtrees appeared to be still in progress. However, the formerwere far less effective as food bases for A. mellea than thelatter. Further experimentation may-reveal whether the treatmentsdescribed are practical methods for reducing infection in plantationsestablished on infested hardwood sites. Stump poisoning (withno pre-felling treatment) may also prove effective.     

Infection of Cucumber Cotyledons by Cucumber Mosaic Virus and the Participation of Chlorophyllase in the Development of Chlorotic Lesions

Cotyledon infection of cucumber (Cucumis sativus L. cultivarImproved Telegraph) results in abnormal growth and the appearanceof chlorotic lesions leading to general chlorosis of the cotyledons.The disease causes increased chlorophyll degradation and chlorophyllaseactivity. Virus-induced perturbations in chlorophyllase activityare discussed in relation to current concepts of the role ofthis enzyme in vivo.     

Cruzipain,a major Trypanosoma cruzi antigen,promotes arginase-2 expression and survival of neonatal mouse cardiomyocytes

An intense myocarditis is frequently found in the acute phase of Trypanosoma cruzi infection. Despite the cardiac damage, infected individuals may remain asymptomatic for decades. Thus T. cruzi may directly prevent cardiomyocyte death to keep heart destruction in check. Recently, it has been shown that Schwann cell invasion by T. cruzi, their prime target in the peripheral nervous system, suppressed host cell apoptosis caused by growth factor deprivation. Likewise, the trans-sialidase of T. cruzi reproduced this antiapoptotic activity of the parasite. In this study, we have investigated the effect of cruzipain, another important T. cruzi antigen, on survival and cell death of neonatal BALB/c mouse cardiomyocyte cultures. We have found that cruzipain, as well as T. cruzi infection, promoted survival of cardiomyocytes cultured under serum deprivation. The antiapoptotic effect was mediated by Bcl-2 expression but not by Bcl-xL expression. Because arginase activity is involved in cell differentiation and wound healing in most cell types and it favors parasite growth within the cell, we have further investigated the effect of cruzipain on the regulation of L-arginine metabolic pathways. Our results have revealed that cruzipain enhanced arginase activity and the expression of arginase-2 isoform but failed to induce nitric oxide synthase activity. In addition, the inhibition of arginase activity by N^G-hydroxy-L-arginine, abrogated the antiapoptotic action of cruzipain. The results demonstrate that cruzipain may act as a survival factor for cardiomyocytes because it rescued them from apoptosis and stimulated arginase-2. apoptosis; Bcl-2; Bcl-xL; nitric oxide synthase; nitric oxide     

Role of Cell-wall-degrading Enzymes in the Development of Leaf Spots Caused by Ascochyta pisi and Mycosphaerella pinodes

Extracts of limited and spreading lesions caused by Mycosphaerellapinodes on detached pea leaflets contained proteolytic, cellulolytic,and pectolytic enzymes although only in spreading lesions wasthere much degradation of cell walls. The brown tissue fromlimited M. pinodes lesions was resistant to maceration by enzymesfrom spreading lesions. Limited lesions contained water-soluble,95 per cent ethanol insoluble, partially dialysable, inhibitorsof pectin transeliminase which is probably the macerating enzyme. Green, spreading M. pinodes lesions developed only on leafletsfloating on water. Growth of these lesions was accompanied bycontinous loss of phenolic substances to the water while thephenol content in infected tissue remained similar to that inuninoculated controls. In contrast, the phenol content in mature,limited M. pinodes lesions on leaflets suspended just abovethe water level was about four times that in healthy tissue.It is suggested that loss of phenolics from floating leafletsprevents tissue browning and the development of resistance ofthe cell walls to maceration. But this type of resistance doesnot appear to be a major factor in the limitation of lesionson suspended tissue. Extracts of limited Ascochyta pisi lesions on leaflets floatingon water contained pectolytic and hemicellulolytic enzymes.Some cellulase (Cx) activity was detected although there waslittle evidence of cellulose degradation in cell walls in infectedtissue. The nature of the macerating factor remains uncertainbut it was found that extracts from lesions contained inhibitorsof pectic enzymes and that tissue just beyond that colonizedby the fungus was resistant to maceration; this resistance isprobably important in restricting the growth of the pathogenin the leaf.     

The Angiospermous Root ParasiteOrobancheL. (Orobanchaceae) Induces Expression of a Pathogenesis Related (PR) Gene in Susceptible Tobacco Roots

Parasitic plants develop a haustorium that intrudes host tissues.In roots of transgenic PRb-1b-GUS tobacco the expression ofthe chimeric gene was prominent nearOrobancheinfection. Theexpression of the pathogenesis related (PR) protein gene inOrobanche-infectedroots indicates thatOrobanchereleases appropriate elicitors,and that the susceptible plant does senseOrobancheinvasion.TheOrobanche-responsive promoter may be a useful tool in engineeringresistances to this parasitic weed.Copyright 1998 Annals ofBotany Company Haustorium,Nicotiana tabacum, Orobanche aegyptiaca, parasitic plants, PR proteins, tobacco.     

The Infection of Pine stumps by Fomes annosus and other fungi

A study of the infection biology of stump-colonizing fungi hasshown that certain species, for instance Fomes annosus, Peniophoragigantea, Stereum sanguinolentum, and several causing blue-stain,initiate infection of fresh stumps by means of air-borne sporeswhich colonize the cut surface. The incidence of natural infectionis reduced considerably by applying creosote to the surfaceimmediately after felling. High resin content of stumps is correlatedwith increased resistance to infection. Marked seasonal variationin the incidence of stump infection by F. annosus and P. giganteawas observed. The spore content of the air, and competitionbetween fungi in stumps, are considered to be important factorsaffecting this variation. Initial colonization of stump roots usually proceeds from thebody of the stump. Invasion of roots by saprophytes presentin the soil or litter also occurs but only many months afterfelling. Crowns of plantation pines may bear many spores of stump-colonizingfungi, including F. annosus. Under the conditions described,the proportion of stump infections ascribable to rain-splash-bornespores was small compared with that caused by wind-borne spores.     

The effects of Fungi on the Gametophytes of Pteridium aquilinum (L.) Kuhn

I. The prothalli have been shown to be convenient subjects forthe study of some fungal relationships with green plants. Purecultures have been established from all the populations examinedby germination of young spores, and it has been shown that duringdormancy the number of spores which can germinate in pure culturedecreases more rapidly than the number which can germinate incultures containing contaminant fungi. Previous reports of thestimulatory effect of fungi on prothallial growth and developmenthave been confirmed and extended. 2. Prothalli growing on mineral agar have been shown to be potentiallysusceptible to the attack of a wide variety of pathogens ofhigher plants, but only two naturally occurring species of fungipathogenic to prothalli have been found during an examinationof growth on a variety of soils from bracken-infested areasin the west of Scotland. 3. The aetiology of the disease incited by Botrytis cmerca inprothalli has been shown to be similar to that of this diseasein higher plants. The pathogen is some-times restricted to lesionsof limited size around the sites of successful infections andthis is associated with changes in the cell walls of the host.A protopectinase solution prepared from a culture of germinatingspores by Brown's method induced symptoms in the prothallialcells similar to those induced by the attack of the fungus.The cell-attacking properties of the solution were greatly reducedwhen the protopectinase content was inactivated by low heatfor a short time, but they were not entirely destroyed. Thisconfirms previous indications that more than one complex maybe involved in the attack, but since the second moiety demonstratedis at least partially thermolabile the evidence does not supportjudgement of its relative significance in the attacking process.     

Impacts of a native parasitic plant on an introduced and a native host species: implications for the control of an invasive weed

Background and Aims: While invasive species may escape from natural enemies in thenew range, the establishment of novel biotic interactions withspecies native to the invaded range can determine their success.Biological control of plant populations can be achieved by manipulationof a species' enemies in the invaded range. Interactions weretherefore investigated between a native parasitic plant andan invasive legume in Mediterranean-type woodlands of SouthAustralia. Methods: The effects of the native stem parasite, Cassytha pubescens,on the introduced host, Cytisus scoparius, and a co-occurringnative host, Leptospermum myrsinoides, were compared. The hypothesisthat the parasitic plant would have a greater impact on theintroduced host than the native host was tested. In a fieldstudy, photosynthesis, growth and survival of hosts and parasitewere examined. Key Results: As predicted, Cassytha had greater impacts on the introducedhost than the native host. Dead Cytisus were associated withdense Cassytha infections but mortality of Leptospermum wasnot correlated with parasite infection. Cassytha infection reducedthe photosynthetic rates of both hosts. Infected Cytisus showedslower recovery of photosystem II efficiency, lower transpirationrates and reduced photosynthetic biomass in comparison withuninfected plants. Parasite photosynthetic rates and growthrates were higher when growing on the introduced host Cytisus,than on Leptospermum. Conclusions: Infection by a native parasitic plant had strong negative effectson the physiology and above-ground biomass allocation of anintroduced species and was correlated with increased plant mortality.The greater impact of the parasite on the introduced host maybe due to either the greater resources that this host providesor increased resistance to infection by the native host. Thisdisparity of effects between introduced host and native hostindicates the potential for Cassytha to be exploited as a controltool.     

Nutrient Relations of Groundsel (Senecio vulgaris) Infected by Rust (Puccinia lagenophorae) at a Range of Nutrient Concentrations I. Concentrations, Contents and Distribution of N, P and K

Groundsel (Senecio vulgaris L.), healthy or infected with therust fungus Puccinia lagenophorae was grown in sand and fedwith a complete nutrient medium diluted to give a range of concentrations.Analysis of bulked, dried tissues of the plant showed that undernutrient-rich conditions rust infection resulted in increasedconcentrations of total (Kjeldahl) nitrogen and potassium buthad little effect on phosphorus concentration. Thus, despitereduced dry weight growth, total plant nitrogen contents wereno less in rusted than control plants. Although total contentsof phosphorus and potassium were reduced by rust, effects wereprobably related to loss of these nutrients in fungal spores. Interactions between rust infection and nutrient supply weresignificant but differed between nutrients: rust caused increasednitrogen concentrations only under nutrient-rich conditionsbut increased phosphorus concentrations only when nutrient supplywas limited. Increased concentrations were not confined to infectedtissues. Mechanisms underlying rust-nutrient interactions appearto be complex and to depend inter alia on the partitioning andrecycling of the particular nutrient within the plant. Rust-inducedincreases in potassium concentration occurred under both highand low nutrient conditions but were confined to infected tissues.Potassium accumulation in nutrient deficient conditions wasprobably due to increased transpirational flux into infectedtissues, but under nutrient-rich conditions reduced potassiumexport appeared to assume greater significance. The possible implications of the changed nutrient relationsfor the wider interactions of rust-infected plants in naturalvegetation are discussed. Senecio vulgaris, Puccinia lagenophorae, rust infection, nutrient deficiency, nutrient content, nutrient concentration, nutrient distribution     

Leaf Spots Induced by Ascochyta pisi and Mycosphaerella pinodes

The leaf-spot pathogens, Ascochyta pisi and Mycosphaerella pinodes,both cause limited, necrotic lesions in detached pea leafletssuspended above water. When leaflets were floated on water A.pisi lesions were still limited, but those caused by M. pinodesspread rapidly to occupy all the leaflet tissue. Increasing the numbers of spores in inocula decreased numbersof mature lesions caused by A. pisi, but increased numbers ofspreading lesions caused by M. pinodes. Older leaflets weremore susceptible to both pathogens. Studies of penetration and colonization of leaves with the aidof light and electron microscopy showed that cell-wall-degradingenzymes were involved in the formation of A. pisi lesions andin spreading lesions caused by M. pinodes. There was littleevidence of cell-wall degradation in limited M. pinodes lesionsin which penetration of walls by hyphae seemed to be mechanicalin nature. No physical barriers developed in tissues surrounding limitedlesions. Nevertheless, A. pisi was rarely found beyond the necroticarea. This suggested that tissues beyond the lesion had becomeresistant to the parasite. In contrast, M. pinodes often grewoutside the necrotic area, sometimes many days after this hadstopped growing, but when it did so it caused no more necrosisunless leaflets were placed in conditions in which the spreadingtype of lesion could develop.     

Role of Inhibitors of Fungal Growth in the Limitation of Leaf Spots Caused by Ascochyta pisi and Mycosphaerella pinodes

The phytoalexin, pisatin, was detected in host tissues 24 hafter inoculation of pea leaflets with spores of the leaf-spottingpathogens Ascochyta pisi and Mycosphaerella pinodes. Pisatincontinued to accumulate in infected tissue as A. pisi lesionsdeveloped and was present in inhibitory concentrations in thebrown tissue beyond the region colonized by the pathogen. During the formation of limited M. pinodes lesions, concentrationsof pisatin were highest 2 days after inoculation. Levels weremore variable and lower in older lesions which appeared to containno other inhibitors of germ-tube growth. Spreading lesions causedby M. pinodes on leaflets floating on water contained littleor no pisatin although little was released to the water below.These lesions did, however, contain other highly active inhibitorsof germ-tube growth. The significance of these results in terms of limitation oflesions are discussed. The ease with which M. pinodes lesionscan become progressive may reflect the greater ability of thispathogen to grow in high concentrations of pisatin under certainconditions.     

Observations on the Biology of Fomes annosus, with Particular Reference to East Anglian Pine Plantations: III. Natural and Experimental Infection of Pines, and Some Factors affecting Severity of the Disease

Apparently Fomes annosus normally invades healthy, not damaged,roots, the wood being infected almost at once in mall roots,though in larger ones the fungus grows in the bark for sometime. Alkaline soils also favour the latter type of development.Infections of living roots are more frequent around infectedstumps in alkaline soils than in acid ones. Details are given of infection of pine roots induced experimentallyand of the factors affecting invasion. Greater resistance to killing is evinced by older tree and thoseon the margin of the plantation. Disease is leas severe in EastAnglia on acid soils and where there is more organic matteron the soil surface. These relations are apparently associatedwith the types of soil microflora (of which details are given),the antagonism of Trichoderme viride being especially important.     

The Translocation of 14C-Labelled Assimilates in Dwarf Bean Plants Infected with Xanthomonas phaseoli (E.F.Sm.) Dowson

The distribution of ¹⁴C-labelled assimilates in dwarf beansinfected on one unifoliate with Xanthomonas phaseoli or systemicallyinfected with the pathogen was compared with the distributionin plants subjected to water stress. Unifoliates on systemically-infectedand water-stressed plants retained a much greater proportionof assimilated ¹⁴CO₂ than equivalent leaves on healthy plants,but unifoliates directly inoculated with X. phaseoli (localinfection) retained only a slightly larger proportion than controlplants. Local infection had little influence on the distribution ofexported radiocarbon but systemic infection produced markedeffects and there were similar changes in water-stressed plants.These changes seem to be related mainly to changes in growthpatterns, particularly to the reduced development of trifoliateleaves. The main causes of the altered assimilate distributionappear to be modified source-sink relationships, but the natureof the vascular system of dwarf bean and interference with vascularfunction by X. phaseoli seem to be more significant factorsthan in other diseases where assimilate distribution has beenstudied.     

Comparative study on the gametophyte morphology and development of three paramo species of Jamesonia (Pteridaceae,Polypodiopsida)

The sexual phase of three species of Jamesonia (J. imbricata, J. rotundifolia and J. scammaniae) has been studied, from spore germination to gametangia formation, with special attention to the morphological development of prothalli. This is the first work to deal with gametophytes of species in this genus. All three species have trilete, tetrahedrical spores that germinate following the Vittaria type. The developmental pattern of J. imbricata and J. rotundifolia is intermediate between the Adiantum and Ceratopteris types, as the initial mitotic activity is assumed by an obconical apical cell, substituted later by a lateral meristem. In J. scammaniae, no apical cell or lateral meristem is formed, so the prothalli remain ameristic throughout the developmental process. Adult gametophytes are naked and variable in shape, in the same species ranging from typical cordate prothalli to irregularly lobed forms. Gametangia of normal shape and size was observed in both J. imbricata and J. rotundifolia, but not in J. scammaniae. Apogamy could be expected to occur in the genus, a phenomenon to be examined in the future. Comparisons are made with known species of related genera and results are discussed from an ecological perspective in the paramo environment.     

Fungal Associations: III. The Role of Pectic Enzymes on the Synergistic Relation between Rhizoctonia solani Kuhn and Fusarium solani Snyder and Hansen, in the Rotting of Potato Tubers

The greatest activity of protopectinase obtained from the growthof Rhizoctonia solani and Fusarium solani on autoclaved potatoplugs occurred at pH 6.5, and greatest activity of the ‘lossof viscosity’ enzyme was found at 6–5 for Rhizoctonia,and between 6.5 and 8.3 for Fusarium. Protopectinase enzymeobtained from double infections of the Fusarium spp. with Rhizoctonia,or by mixing the enzymes of individual Fusarium spp. with Rhizoctoniaenzyme, were more active than the enzymes from single inoculations.Cylindrocarpon radicicola enzyme was more active when obtainedfrom a pure culture than from double infection. Similarly, mixingthis enzyme with the enzyme of Rhizoctonia reduced its activity.The evidence indicated that the protopectinase of Rhizoctoniawas similar to that of Cylindrocarpon and differed from thatof the Fusarium spp. Using paper partition chromatography, two bands from Rhizoctoniacrude enzyme had a stimulatory effect on Fusarium enzyme, whileonly one band from Fusarium enzyme stimulated Rhizoctonia enzyme. The purified enzyme of Rhizoctonia degraded pectin to galacturonicacid. Fusarium pure enzyme degraded pectin to an intermediatestage. A mixture of the two enzymes degraded pectin to galacturonicacid, without the intermediate stage formed by Fusarium alonebeing detected. The role played by pectic enzymes upon the synergistic relationof Rhizoctonia solani and Fusarium solani on rotting potatotubers is discussed.     

Scanning Electron Microscopy of the Infection of Beans by Rhizoctonia solani Propagules

Germination, hyphal spread, and formation of infection cushionsand lesions on bean hypocotyls by infective large propagulesof Rhizoctonia solani were studied with the scanning electronmicroscope. The surface of old, but not of young, hyphae appearedtypically wrinkled and shrunken. Infection cushions appearedas a network of several layers of crossed anastomosing hyphae.These features could not be observed under the light microscope.No differences in the surfaces of infective and non-infectivesmall propagules could be observed. Non-infective propagulesgerminating on the hypocotyls gave rise to spreading hyphaebut did not develop infection cushions.     

Infection of the diatom Asterionella by a chytrid. I. Effects of light on reproduction and infectivity of the parasite

The influence of hight limitation of the diatom Asterionellaformosa Hass, on the growth-determining parameters of its fungalparasiteRhizophydium planktonicum Canter emend, was measured,using laboratory cultures of both organisms. The experimentswere earned out at 6°C under a 15:9 h light-dark cycle.At saturating light conditions, the mean zoospore productionof the parasite was 23.4 zoospores sporangium^–1, and themean development time of the sporangia was 7 9 days. Light limitationof the host caused a substantial decrease of the zoospore production,while the development time was only slightly reduced. The improvedzoospore production at high light intensities was mainly theresult of incorporation of photosynthetic products generatedby the host after infection. Under limiting light conditions,Asterionella cells were less susceptible to infection withfungal zoospores. No infection at all occurred below 2 µEm^–2 s^–1, a light intensity that still supportedsome algal growth The maximum infection rate indicated thatchemotactic attraction of the parasite's zoospores by extracellularproducts of the host is involved. The infective lifetime ofthe zoospores of the parasite did not depend on light conditions,and was estimated at 8 days. The measured zoospore productionrates, both under limiting and saturating light conditions,enable the parasite to exceed the specific growth rate of thehost, and thus become epidemic, at sufficiently high host densities.