Thrust reversal by tubular mastigonemes: immunological evidence for a role of mastigonemes in forward motion of zoospores ofPhytophthora cinnamomi

Summary The role of tubular mastigonemes in the reversal of thrust of the anterior flagellum ofPhytophthora cinnamomi was analysed using mastigoneme-specific monoclonal antibodies and immunoflu-orescence and video microscopy. Exposure of live zoospores ofP. cinnamomi to the mastigoneme-specific Zg antibodies caused alterations in the arrangement of mastigonemes on the flagellar surface and at Zg concentrations above 0.3 /ml, mastigonemes became detached from the flagellum. As a consequence of antibody binding to the mastigonemes there were concentration-dependent perturbations in zoospore swimming behaviour and anterior flagellum beat pattern. With increasing antibody concentration zoospores swam more slowly and other parameters of their swimming pattern, such as the wavelength of the swimming helix and the frequency of rotation, were also reduced. The effects of Zg antibodies were specific at two levels: control immunoglobulins or antibodies that bound to other flagellar surface components did not have an effect on motility, and Zg antibodies did not interfere with the motility of zoospores of oomycete species to which they did not bind. The effects of antibody-induced disruption of mastigoneme arrangement strongly support previous hypotheses that tubular mastigonemes are responsible for thrust reversal by the anterior flagellum, enabling it to pull the cell through the surrounding medium.     

ULTRASTRUCTURE OF SWARMERS IN THE LAMINARIALES (PHAEOPHYCEAE). II. SPERM1

The ultrastructure of sperm from 13 species in 11 genera of Laminariales collected in the northeast Pacific Ocean is unique in the brown algae. The sperm are elongate, and possess a nucleus, several mitochondria and two or three chloroplasts, but no eyespot. The anterior flagellum bears mastigonemes on the proximal half of its length; a distal “whiplash” portion lacks mastigonemes and is an extension of only the two central singlet microtubules of the axoneme. A peculiar feature of these sperm is the posterior flagellum, which is longer than the anterior flagellum and tapers distally as the doublet microtubules become singlets and decrease in number. This feature contrasts with the laminarialean zoospore, which possesses a short posterior flagellum with the usual “9 + 2” axoneme. The structure of these sperm differs from that reported for Chorda, the sperm of which resembles a primitive brown algal zoospore. The facts support the concept that Chorda is the most primitive member of the Laminariales.     

Monoclonal antibodies to cell surface components of zoospores and cysts of the fungusPythium aphanidermatum reveal species-specific antigens

A panel of monoclonal antibodies (MAbs) designated PA1 to PA8 has been raised against cell surface components of zoospores and cysts of the pathogenic fungusPythium aphanidermatum. The antibodies were selected on the basis of binding assays using indirect immunofluorescence. Four binding patterns were observed: PA1 labeled the entire zoospore surface including both flagella, PA2 binding was restricted to the anterior flagellum, PA3–PA6 bound to the adhesive cell coat secreted by zoospores during encystment, and PA7 and PA8 labeled zoospores and the cyst cell wall. Electron microscopic immunogold labeling of zoospores showed that PA2 bound to the mastigonemes on the anterior flagellum. The MAbs were tested for binding to zoospores and cysts of several isolates ofP. aphanidermatum, and to zoospores and cysts of several species ofPythium, Phystophthora, Aphanomyces, andSaprolegnia. The results showed that the antigens recognized by MAbs PA1–PA6 were restricted toP. aphanidermatum, whereas those recognized by PA7 and PA8 occurred on all species tested.     

THE STRUCTURE, ORIGIN, ISOLATION, AND COMPOSITION OF THE TUBULAR MASTIGONEMES OF THE OCHROMONAS FLAGELLUM

The structure, assembly, and composition of the extracellular hairs (mastigonemes) of Ochromonas are detailed in this report. These mastigonemes form two lateral unbalanced rows, each row on opposite sides of the long anterior flagellum. Each mastigoneme consists of lateral filaments of two distinct sizes attached to a tubular shaft. The shaft is further differentiated into a basal region at one end and a group of from one to three terminal filaments at the free end. Mastigoneme ontogeny as revealed especially in deflagellated and regenerating cells appears to begin by assembly of the basal region and shaft within the perinuclear continuum. However, addition of lateral filaments to the shaft and extrusion of the mastigonemes to the cell surface is mediated by the Golgi complex. The ultimate distribution of mastigonemes on the flagellar surface seems to be the result of extrusion of mastigonemes near the base of the flagellum, and it is suggested that mastigonemes are then pulled up the flagellum as the axoneme elongates. Efforts to characterize mastigonemes biochemically after isolation and purification on cesium chloride (CsCl) followed by electrophoresis on acrylamide gels have demonstrated what appear to be a single major polypeptide and several differentially migrating carbohydrates. The polypeptide is not homologous with microtuble protein. The functionally anomalous role of mastigonemes in reversing flagellar thrust is discussed in relation to their distribution relative to flagellar anatomy and to the plane of flagellar undulations.     

Behaviour of Phytophthora cinnamomi Zoospores on Roots of Four Avocado Cultivars

Scanning electron microscopy was used to study the behaviour of Phytophthora cinnamomi zoospores on the roots of three tolerant avocado cultivars. Duke 7, G6 and Martin Grande, and a susceptible Edranol cultivar. Zoospores were attracted to the region of cell elongation and encysted on the roots of all cultivars studied. Adhesion of the zoospores appeared to be aided by root slime. Cysts usually produced one germ tube which penetrated the root directly, or formed an appressorium-like swelling before penetration occurred. Extensive growth of germ tubes occurred where zoospores germinated some distance behind the region of elongation. Cysts germinating behind this region often formed branched germ tubes and more than one appressorium-like swelling. There were no clear differences in the type of pre-penetration structures, formed by zoospore cysts, on the roots of the different avocado cultivars.     

Regulation of attachment, germination, and appressorium formation by zoospores ofLagenidium giganteum and related oomycetes by chitin, chitosan, and catecholamines

Summary Lagenidium giganteum (Oomycetes: Lagenidiales), a facultative parasite of mosquito larvae, infects the larval stage of most species of mosquitoes and a very limited number of alternate hosts. Host infection by this and other members of Oomycetes is initiated by motile, laterally biflagellate zoospores. Chemical bases for the various degrees of host specificity exhibited by these parasites is not known, but presumably involves receptors on the zoospore surface recognizing compounds either secreted by or on the surface of their hosts. Surface topography had no detectable effect onL. giganteum encystment or appressorium formation. Scanning electron microscopy documented the detachment of flagella during zoospore encystment. Bulbous knobs at the basal end of the detached flagellum were interpreted as encysting zoospores dropping the axoneme and/or the basal body and associated structures to which flagella are attached. Multiple signals appear to be involved in the initial steps ofL. giganteum host invasion. Zoospores of this parasite did not encyst on powdered preparations of chitin or chitosan (deacetylated chitin). Upon dissolution of chitosan in dilute acid followed by drying these solutions to form thin, transparent films, zoospores readily encysted. The degree of reacetylation of these films and the spacing of acetylated and deacetylated residues had no significant effect on zoospore encystment. Zoospores of a strain ofLagenidium myophilum isolated from marine shrimp, that also infects mosquito larvae, encysted on chitosan films. No encystment of spores of the plant parasitePhytophthora capsici was observed on chitin or chitosan films. Simulation of cuticle sclerotization by incubating chitosan films with different catecholamines and tyrosinase significantly reduced zoospore encystment. Zoospores that encysted on chitosan films did not germinate in distilled water. Germination could be induced by adding microgram quantities of bovine serum albumin or proteins secreted by motile zoospores into the water, and to a lesser degree by some amino acids, but not by various cations. Zoospores encysted and germinated on the pupal stage of some mosquito species. Appressoria were occasionally formed, but most subsequently sent out another mycelial branch, apparently without attempting to pierce the pupal cuticle. Methylation of pupal exuviae with ethereal diazomethane or methanol/HCl significantly increased zoospore encystment. Modification of chitin by catecholamines, lipids and protein on the epicuticular larval surface all affected host invasion.Abbreviations BSA bovine serum albumin - CID collision-induced dissociation - DOPA 3,4-dihydroxyphenylalanine - ESI-MS electrospray mass spectrometry - ESI-MS/MS tandem electrospray mass spectrometry - SDS-PAGE sodium dodecyl sulphate polyacrylamide gel electrophoresis - WGA wheat germ agglutinin - ZAP zoospore aggregation pheromone     

Centrin association with the flagellar apparatus in spores ofPhytophthora cinnamomi

Summary Antibodies raised against the calcium-binding protein centrin, were used to identify and localise centrin containing structures in the flagellar apparatus of zoospores and cysts of the oomycetePhytophthora cinnamomi. Immunoblotting of extracts from zoospores indicates that theP. cinnamomi centrin homologue is a 20 kDa protein. Immunofluorescence microscopy with anti-centrin antibodies reveals labelling in the flagella, the basal body connector and co-localisation along the microtubular R1 root (formerly called AR3) that runs from the right side of the basal body of the anterior flagellum into the anterior of the zoospore close to the ventral surface. The centrin (R1^cen) and tubulin components of the R1 root split into four loops on the right hand side of the ventral groove and rejoin along the left hand side of the groove. The R1 root continues down the left hand side of the zoospore past the basal bodies and parallel to the R4 root. We propose that at least inP. cinnamomi there is no R2 root. Immunogold labelling confirms that centrin is a component of the basal body connector complex. When the zoospores become spherical during encystment, the R1^cen pivots by approximately 90 ° with respect to the nucleus.     

Structure of Labyrinthula sp. Zoospores*

SYNOPSIS. A species of Labyrinthula closely resembling L. algeriensis was isolated from marsh grass, Spartina alterniflora. Zoosporulation was obtained in ～50% of the cultures, which were grown on a modified Vishniac medium, when yeasts were used as food organisms; when the temperature was ～22 C; when thiamine (0.2 mg/l, biotin (1 μg/l, Ba (1 μg/l, and cholesterol (5 mg/l) were present; and when the cells were grown on a semisolid medium (0.6% agar) rather than higher concentrations of agar. The motile cells were similar to biflagellated fungal zoospores in that they were pyriform and laterally biflagellated. The anterior flagellum (13-15 μ long) possessed what appeared to be 2 rows of mastigonemes and was uniform in diameter while the posterior flagellum (6-10 μ) lacked mastigonemes and was tapered distally into a whiplash. The planonts are apparently not isogametes since planogametic copulation could not be induced and since synaptinemal complexes were not observed in sectioned presporangia.     

Ultrastructural evidence for the biflagellate origin of the uniflagellate fungal zoospore

Summary The morphological similarities between the kinetosome and the second centriole of the zoospores of Phlyctochytrium kniepii and P. punctatum (Chytridiomycetes) suggest that the second centriole in the chytrid zoospore is a vestigial flagellum base. It is suggested that the term vestigial kinetosome may also be used when referring to the structure which is presently termed the second centriole of the chytrid zoospore. Morphological similarities between the chytrid zoospores of P. kniepii and P. punctatum and the zoospores of Rhizidiomyces apophysatus (Hyphochytridiomycetes) are noted. The possible biflagellate origin of fungi with uniflagellate zoospores is discussed. The third fiber (C fiber) of the kinetosome triplet is shown to form as an outgrowth of the B fiber of the kinetosome doublet.     

Effects of concanavalin A on the net formation of zoospores in Hydrodictyon reticulatum (Chlorococcales, Chlorophyceae)

In the green alga Hydrodictyon reticulatum (L.) Lager‐heim (Chlorococcales, Chlorophyceae), zoospores are arranged in a regular fashion to form an intricate hexagonal network during the asexual reproductive cycle. Polypeptides that bind concanavalin A (Con A) in zoospores increased in amount during net formation and decreased after the completion of the adhesion between zoospores. Fluorescein isothiocyanate‐Con A‐binding sites corresponded to the contact sites of zoospores immediately after cessation of the movement. Treatment with 25 μg mL^?1 Con A inhibited adhesion of isolated immotile zoospores obtained from parental cells, and Con A‐treated zoospores could not form hexagonal nets. Moreover, when isolated immotile zoospores were treated with Con A, the cessation of the zoospore movement was retarded in dose‐dependent manner. These results suggest that the Con A‐binding sites may participate in the adhesion of zoospores during hexagonal net formation.     

Synthesis and assembly of flagellar surface antigens during zoosporogenesis inPhytophthora cinnamomi

Summary Cryomicrotomy and immunofluorescence microscopy employing three different categories of monoclonal antibody (MAb) that label antigens on the surface of one or both flagella ofPhytophthora dnnamomi have been used to follow the synthesis and assembly of flagellar surface components. MAb Zf 1 binds to the surface of both the anterior tinsel and posterior whiplash flagella, as well as to a nuclear component. The labeling of the flagella is punctate in nature, is brighter at the flagellar base, and does not always extend to the distal tip of the flagella. MAbs in the Zt group recognise an antigen that is located along the sides of the tinsel flagellum and may be associated with the base of the mastigonemes. Immunodot-blot analysis has shown that binding of Zt MAbs is abolished by pretreatment with either pronase or periodate oxidation indicating that the antigen is a glycoprotein. MAbs in the Zg group bind to the mastigonemes on the tinsel flagellum and to packets of mastigonemes in the cytoplasm of zoospores. Zt and Zg antigens increase in abundance during zoosporogenesis and are present throughout the life cycle of the fungus, whereas the non-nuclear localisation of the Zf antigen appears only during sporulation. Prior to association with the flagellar surface, all three components become clustered in the groove region of zoospores. They do not become associated with the flagellar surface until at least 15 min after the flagellar axoneme has formed.Abbreviations BSA bovine serum albumin - DAPI 4,6-diamidino-2-phenylindole - DMF dimethylformamide - lgG₁ immunoglobulin G₁ - MAbs monoclonal antibodies - NIM non-immune mouse antibodies - PBS phosphate-buffered saline - PBST phosphate-buffered saline with 0.5% Tween 20 - PIPES 1,4-piperazinediethanesulfonic acid - PPD paraphenylenediamine dihydrochloride - RT room temperature - TBS tris-buffered saline - TEST tris-buffered saline with 0.05% Tween 20     

Quantification of laminarialean zoospores in seawater by real‐time PCR

Laminarialean plants undergo heteromorphic alternation of generations between the macroscopic diploid sporophyte and the microscopic haploid gametophyte. The generations change through the formation and release of asexual or sexual reproductive cells. It is difficult to monitor the release and diffusion of zoospores into the environment. Furthermore, even if zoospores can be detected, species identification remains difficult. This study attempted to develop a sensitive and fast identification method for laminarialean zoospores using quantitative PCR. In addition, we aimed to estimate the density of zoospores in natural seawater. Specific primers for Saccharina japonica and Undaria pinnatifida were designed and used to estimate the quantity of zoospores in seawater. DNA samples (environmental DNA) were collected from seawater once or twice each month for 2 years at the same area, and seasonal variations in the release of zoospores was monitored. The estimated maturation period based on the number of released zoospores in this study was comparable with those of the previously reported maturation periods of S. japonica and U. pinnatifida sporophytes. This supports the validity of our method in estimating zoospore release from laminarialean plants. The method will be a useful tool for ecological studies on these commercially relevant species.     

ULTRASTRUCTURE OF THE RESERVOIR AND FLAGELLA IN PHACUS PLEURONECTES (EUGLENOPHYCEAE)1

The ultrastructure of the reservoir region of Phacus pleuronectes is described. Thin sections, ruthenium red staining, and shadow-cast preparations elucidate relationships and structural details of the flagella and flagellar hairs or mastigonemes. A heretofore undescribed structure in Phacus, the multitubular structure (MTS), with associated fibrillar projections, is reported. The MTS is located in the cytoplasm at the distal region of the reservoir near the contractile vacuole. A coordinated function of the MTS and adjacent fibrillar projections is suggested. The occurrence of mastigonemes along the entire length of the emergent flagellum is suggested, in contrast to earlier reports of their presence only on that portion of the flagellum distal to the cytostome. The present investigation postulates also that the mastigonemes are bipartite, the thicker fibrous bases becoming modified distally into the classically described, mastigonemes.     

THE EFFECTS OF HIGH IRRADIANCE ON THE SETTLEMENT COMPETENCY AND VIABILITY OF KELP ZOOSPORES1

Elevated irradiance has a profound effect on the successful dispersal and establishment of kelp zoospores, affecting their physiology and viability. The research to date, however, has been on zoospores localized near the benthos, with little attention on the importance of vertical transportation and subsequent exposure to increased irradiance. Therefore, we wanted to investigate the effects of exposure to high irradiance on the reproductive planktonic life‐history stages of kelps Macrocystis pyrifera (L.) C. Agardh and Pterygophora californica Rupr. Zoospores of both species were exposed to different irradiances (75, 275, 575, 1,025 μmol photons · m^?2 · s^?1) over varying durations (1, 2, 4, 8, 12 h) and subsequently monitored for settlement competency, gametophyte development, and reproductive viability. Settlement success for M. pyrifera was uniform throughout all irradiance × time treatments, while settlement for P. californica decreased with increasing exposure time but not irradiance, although settlement was generally reduced at the highest irradiance level. Following zoospore settlement, germ tube development was visible in the gametophytes of both species within 1 week, although a significant decline of germ tube density in P. californica was observed with increasing irradiance. Similarly, a decrease in germ tube development with increasing exposure was observed across all irradiance levels for M. pyrifera, but irradiance itself was not significant. Further development into embryonic sporophytes was remarkably similar to gametophyte development, suggesting that the effect of exposure of kelp zoospores to high irradiance on subsequent sporophyte production is mediated through gametophyte development as well as zoospore survival.     

Early development in an algal gametophyte: role of the cytoskeleton in germination and nuclear translocation

Summary Biflagellate zoospores from the giant kelpMacrocystis pyrifera underwent germination after adhering to a substrate and produced germ tubes that were approximately 13–15 m in length. Coincident with the germ tube elongation was organelle (other than the nucleus) translocation along the tube. Shortly after formation of the germ tube, the zoospore nucleus divided and one daughter nucleus translocated along the germ tube. The nucleus did not appear to undergo chromosomal condensation prior to division. The nuclear division and/or translocation of the daughter nucleus did not begin until well after germ tube elongation was complete, demonstrating that these are temporally distinct developmental events. The translocation of one daughter nucleus coincided with differentiation of the distal end of the germ tube into a bulbous structure. Following this, the first gametophytic cross wall was formed and, subsequently, the daughter nucleus remaining in the original zoospore body underwent repositioning, assuming a position in the germ tube near the cross wall. Cytochalasin D inhibited germ tube elongation suggesting that actin microfilaments are probably involved in this developmental process. In addition, when cytochalasin D was added to the culture after the germ tube elongation was complete, it did not affect either nuclear division or translocation, indicating that microfilaments were not directly involved in these nuclear events. Colchicine and the plant specific microtubule disrupting agent, amiprophos methyl blocked nuclear division and translocation without affecting germination or germ tube elongation. These data suggest that actin microfilaments are primarily responsible for complete germination, specifically germ tube elongation, while microtubules are involved in nuclear division and translocation. The present study demonstrates that germination (and germ tube elongation) and nuclear translocation inM. pyrifera gametophytes are temporally and mechanistically distinct developmental events.     

ZOOSPOROGENESIS,MORPHOLOGY, ULTRASTRUCTURE,PIGMENT COMPOSITION,AND PHYLOGENETIC POSITION OF TRACHYDISCUS MINUTUS (EUSTIGMATOPHYCEAE,HETEROKONTOPHYTA)1

The traditional order Mischococcales (Xanthophyceae) is polyphyletic with some original members now classified in a separate class, Eustigmatophyceae. However, most mischococcalean species have not yet been studied in detail, raising the possibility that many of them still remain misplaced. We established an algal culture (strain CCALA 838) determined as one such species, Trachydiscus minutus (Bourr.) H. Ettl, and studied the morphology, ultrastructure, life cycle, pigment composition, and phylogeny using the 18S rRNA gene. We discovered a zoosporic part of the life cycle of this alga. Zoospore production was induced by darkness, suppressed by light, and was temperature dependent. The zoospores possessed one flagellum covered with mastigonemes and exhibited a basal swelling, but a stigma was missing. Ultrastructural investigations of vegetative cells revealed plastids lacking both a connection to the nuclear envelope and a girdle lamella. Moreover, we described biogenesis of oil bodies on the ultrastructural level. Photosynthetic pigments of T. minutus included as the major carotenoids violaxanthin and vaucheriaxanthin (ester); we detected no chl c. An 18S rRNA gene‐based phylogenetic analysis placed T. minutus in a clade with species of the genus Pseudostaurastrum and with Goniochloris sculpta Geitler, which form a sister branch to initially studied Eustigmatophyceae. In summary, our results are inconsistent with classifying T. minutus as a xanthophycean and indicate that it is a member of a novel deep lineage of the class Eustigmatophyceae.     

Characterization of zoospore and cyst surface structure in saprophytic and fish pathogenicSaprolegnia species (oomycete fungal protists)

Summary The importance of the surface structure and chemistry in zoospores and cysts of oomycetes is briefly reviewed and the organelle systems associated with encystment described. The surface structure and chemistry of primary and secondary zoospores and cysts ofSaprolegnia diclina (a representative saprophytic species) andS. parasitica (a representative salmonid fish pathogen) were explored using the lectins concanavilin A (Con A) and wheat germ agglutinin (WGA) and monoclonal antibodies (MAbs) raised against a mixed zoospore and cyst suspension ofS. parasitica. The binding of lectins and antibodies to spores was determined using immunofluorescence microscopy with fluorescein isothiocyanate-labelled probes and with electron microscopy with gold-conjugated probes applied to spore suspensions post-fixation. In both species Con A, which is specific for glucose and mannose sugars, bound to both the surface of primary and secondary zoospores (the surface glycocalyx) and their cyst coats and readily induced zoospore encystment. The binding to the cysts appeared to be mainly associated with the matrix material released from the primary and secondary encystment vesicles and which appeared to diminish with time. No binding to germ tube walls was observed with this lectin. The MAb labelling showed a generally similar binding pattern to the primary and secondary cysts to that observed with Con A, although the binding to zoospores was more variable. Primary zoospores bound the antibodies but secondary zoospores appeared less reactive. It is suggested that the MAbs share a common epitope with one or more of the Con A-binding components. In both species WGA, which is specific for amongst other things the sugar N-acetyl glucosamine, bound to localised apical patches on the primary zoospores. This lectin also binds to the ventral groove region of secondary zoospores ofS. diclina, which were induced to encyst by this lectin. In contrast secondary zoospores ofS. parasitica were not induced to encyst by the addition of WGA and showed a patchy dorsal binding with this lectin. WGA also binds to both the inner wall of discharged primary cysts and the young germ tube walls of both species. These observations are discussed both in relation to other oomycete spores and to their possible functional and ecological significance.Abbreviations BSA bovine serum albumin - Con A Concanavalin A - DBA Dolichos biflorus agglutinin - ELISA enzyme-linked immunosorbent assay - EM electron microscope - EV encystment vesicles - FCS foetal calf serum - FITC Fluorescein isothiocyanate - FV peripheral fibrillar vesicles - G+F 0.2% glutaraldehyde and 2.0% formaldehyde primary fixative solution - 2G 2% glutaraldehyde primary fixative - LM light microscopy - MAbs monoclonal antibodies - LPV large peripheral vesicles - PBS phosphate buffered saline - PCV flattened peripheral cisternae - PEV primary encystment vesicle - PIPES piperazine-N,N1-bis(2-ethane sulfonic acid) - PNA Ricinus communis agglutinin - RAM-FITC/Au_10–20 Fluorescein isothiocyanate/gold (10 or 20 nm) labelled rabbit anti-mouse immunoglobulin - RCA Ricinus communis agglutinin - SEM scanning electron micrograph - SBA soybean agglutinin - SEV secondary encystment vesicles - TEM transmission electron micrograph - UEA I Ulex europaeus agglutinin - WGA wheat germ agglutinin     

GLYCOCONJUGATE ORGANIZATION OF ENTEROMORPHA (=ULVA) FLEXUOSA AND ULVA FASCIATA (CHLOROPHYTA) ZOOSPORES1

Ecologically successful algae that colonize natural and artificial substrates in the marine environment have distinct strategies for opportunistic dispersal and settlement. The objective of this research was to visualize molecular architecture of zoospores from Enteromorpha (=Ulva) flexuosa (Wulfen) J. Agardh and Ulva fasciata Delile that coexist but alternate in dominance on an intertidal bench. Multiple fluorescent lectins were used to stabilize and probe for diverse zoospore glycoconjugates (GC) that could be involved in cell and substrate interactions. Results from epifluorescence microscopy showed distinct cellular and extracellular polymeric substance (EPS) domains of GC relative to settlement morphologies. Glycoconjugates were similar for both species with (1) α‐d mannose and/or glucose moieties localized on flagella, the anterior domes and anterior regions, the plasma membranes, and EPS; (2) α‐fucose localized on flagella and anterior regions; (3) N or α,ß‐N acetylglucosamine localized on flagella, the anterior regions, and EPS; and (4) varied N‐acetylgalactosamine and/or galactose moieties localized on each domain for both species excluding the plasma membranes. Some differences in lectin binding were observed for each species at the flagella, the anterior domes, and the plasma membranes. Glycoconjugate distributions shifted with morphological changes that followed initial adhesion. TEM of E. flexuosa zoospore stages following carbohydrate‐stabilizing fixations and gold‐conjugated lectin probes resolved GC with α‐d mannose and/or glucose, and/or N‐acetylglucosamine at the plasma membrane, ER and diverse vesicles of the anterior pole, EPS, and discontinuous regions or knobs associated with flagellar surfaces. The distinct distribution and diversity of zoospore GC may be central to recognition and attachment on diverse substrata by these algae.     

Forecasting infections of the red rot disease on Porphyra yezoensis Ueda (Rhodophyta) cultivation farms

Pythium porphyrae is a fungal pathogen responsible for red rot disease of the seaweed Porphyra (Rhodophyta). Infection forecasts of Porphyra by P. porphyrae were estimated from the epidemiological observations of Porphyra thalli and numbers of zoospore of P. porphyrae in laboratory and cultivation areas. Four features of forecasting infections were determined by relating zoospore concentrations to the incidence of thallus infection; infection (in more than 1000 zoospores L⁻¹), microscopic infection [less than 2 mm in diameter of lesion (in from 2000 to 3000 zoospores L⁻¹)], macroscopic infection [more than 2 mm in diameter of lesion (in from 3000 to 4000 zoospores L⁻¹), and thallus disintegration (in more than 4000 zoospores L⁻¹). High zoospore concentrations led to more infection. The tendency that zoospore concentration of P. porphyrae increased with the rate of infection of Porphyra thalli was generally observed in forecasting infections in both the laboratory and in cultivation areas. Based on the Porphyra cultivation areas, the accuracy and consistency of forecasting infections suggest that this method could be employed to manage and control red rot disease.