Hydroid defenses against predators: the importance of secondary metabolites versus nematocysts

Marine hydroids are commonly thought to be defended by stinging organelles called nematocysts that penetrate predator tissues and inject proteinaceous venoms, but not all hydroids possess these nematocysts. Although an increasing number of bioactive secondary metabolites have been isolated from marine hydroids, ecological roles of these compounds are poorly known. To test the hypothesis that nematocysts and noxious secondary metabolites represent alternative defenses against predation, we examined hydroids from North Carolina, United States for: (1) the palatability of whole polyps before and after nematocysts had been deactivated; (2) the palatability of their chemical extracts; and (3) their nutritional value in terms of organic content, protein content, and levels of refractory structural material (chitin). All hydroids were avoided by a generalist predator, the pinfish Lagodon rhomboides, compared with palatable control foods. Two of these (Halocordyle disticha and Tubularia crocea) became palatable after being treated with potassium chloride to discharge their nematocysts, suggesting that these species rely on nematocysts for defenses against predators. Chemical extracts from nematocyst-defended species had no effect on fish feeding. The four species that remained unpalatable after nematocysts had been discharged (Corydendrium parasiticum, Eudendrium carneum, Hydractinia symbiolongicarpus, Tridentata marginata) possessed chemical extracts that deterred feeding by pinfish. We have isolated and characterized the structures of the deterrent metabolites in two of these species. We found no differences in nutritional content or levels of chitin between nematocyst-defended and chemically defended species, and no evidence that either of these played a role in the rejection of hydroids as prey. Our results suggest that, among hydroids, chemical defenses may be at least as common as nematocyst-based defenses and that the two may represent largely alternative defensive strategies. The four hydroid species with deterrent extracts represent four families and both sub-orders of hydroids, suggesting that chemical defenses in this group may be widespread and have multiple origins. Received: 25 May 1999 / Accepted: 1 February 2000     

The hydroid fossil record and analytical techniques for assessing the affinities of putative hydrozoans and possible hemichordates

Hydrozoan cnidarians are widespread in modern environments, but their polyps or hydroids, when not biomineralized, are generally rare in the fossil record. To assess the affinities of four hydrozoan taxa previously described on the basis of supposed fossils of non‐biomineralized hydroids, we re‐analysed the type specimens of these taxa using a combination of light and electron microscopic tools, including backscattered electron (BSE) scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDS). New morphological, ultrastructural and taphonomic data were generated for Archaeoantennularia byersi from the Devonian of Michigan, Archaeocryptolaria compacta from the Ordovician of Virginia, and Mazohydra megabertha and Drevotella proteana from the Carboniferous Mazon Creek Lagerstätte of Illinois, which are preserved as carbonaceous fossils, aluminosilicate films and iron carbonate minerals in siderite concretions, respectively. In the context of these results, we provide a review of the fossil record of non‐biomineralized hydroids, describe possible biases and changes through time in their occurrence and preservation, and evaluate the criteria commonly used to identify and interpret their fossils. Although hydroids have been reported from Phanerozoic (particularly lower Palaeozoic) rocks around the world, many putative hydroids from the Palaeozoic are poorly substantiated and may actually be hemichordates. Indeed, none of the type specimens in this study represent unequivocal hydrozoans. As shown in BSE images, metatype specimens of A. byersi possess autothecae, fusellae, stolons, stolothecae and bithecae, which decisively indicate that they are dendroid graptolites rather than hydroids. The analyses yielded no evidence that A. compacta, Mazohydra and Drevotella are hydrozoans, as their holotypes lack the diagnostic morphological, taphonomic and ecological features characteristic of purported hydroid analogues. Consequently, our results suggest that many Palaeozoic hydroids may be hemichordates and that interpretations of hydroid fossils should be tested and refined using data collected via in situ analytical techniques like BSE‐SEM and EDS.     

Fine Structure of Hydrolysed Primary Walls in Tracheary Elements of Petiolar Xylem in Eucalyptus delegatensis

The hydrolysed lateral primary walls of tracheary elements ofthe petiolar xylem of Eucalyptus delegatensis were examinedby electron microscopy. Vessel-vessel and vessel—tracheidhydrolysed walls were strikingly different in appearance fromtracheid—tracheid walls. The difference seemed to be inthe degree to which the primary walls were hydrolysed. The observationssuggest the wall hydrolysis to be an ordered and controlledprocess. Eucalyptus delegatensis, hydrolysed wall, petiolar xylem, tracheary elements     

Action of a pure xyloglucan endo-transglycosylase (formerly called xyloglucan-specific endo-(1-4)-β-d-glucanase) from the cotyledons of germinated nasturtium seeds

The action on tamarind seed xyloglucan of the pure, xyloglucan-specific endo-(1→4)-β-D-glucanase from nasturtium (Tropaeolum majus L.) cotyledons has been compared with that of a pure endo-(1→4)-β-D-glucanase (‘cellulase’) of fungal origin. The fungal enzyme hydrolysed the polysaccharide almost completely to a mixture of the four xyloglucan oligosaccharides: Exhaustive digestion with the nasturtium enzyme gave the same four oligosaccharides plus large amounts of higher oligosaccharides and higher-polymeric material. Five of the product oligosaccharides (D,E,F,G,H) were purified and shown to be dimers of oligosaccharides A to C. D (glc₈xyl₆) had the structure A→A, H (glc₈xyl₆gal₄) was C→C, whereas E (glc₈xyl₆gal), F (glc₈xyl₆gal₂) and G (glc₈xyl₆gal₃) were mixtures of structural isomers with the appropriate composition. For example, F contained B₂→B₂ (30%), A→C (30%), C→A (20%), B₂B₁ (15%) and others (about 5%). At moderate concentration (about 3 mM) oligosaccharides D to H were not further hydrolysed by the nasturtium enzyme, but underwent transglycosylation to give oligosaccharides from the group A, B, C, plus higher oligomeric structures. At lower substrate concentrations, hydrolysis was observed. Similarly, tamarind seed xyloglucan was hydrolysed to a greater extent at lower concentrations. It is concluded that the xyloglucan-specific nasturtium-seed endo-(1→4)-β-D-glucanase has a powerful xyloglucan-xyloglucan endo-transglycosylase activity in addition to its known xyloglucan-specific hydrolytic action. It would be more appropriately classified as a xyloglucan endo-transglycosylase. The action and specificity of the nasturtium enzyme are discussed in the context of xyloglucan metabolism in the cell walls of seeds and in other plant tissues.     

Comparison of the surface structures of choline-less Torulopsis pintolopesii grown on defined media with choline or methionine

Summary The chemical composition of cell walls from choline-less Torulopsis pintolopesii grown with choline or with methionine was studied. Methioninegrown cells synthesized a weakened cell wall compared to normal choline-grown yeast. The ethylenediamine fractionation procedure yielded three fractions—A, B, and C—with different solubilities. Glucose and mannose were detected in hydrolysed unfractionated cell walls from yeasts grown under both conditions as well as in all fractions. Glucose content was greater in fractions B and C from methioninegrown cells; the mannose content was about the same. Walls from choline-grown cells (W _c ) had 25% more protein than walls from methionine-grown cells (W _m ). The amino acid composition of the proteins of W _c and W _m was not qualitatively altered. Seventeen amino acids were identified; glutamic and aspartic acids and valine predominated. W _c had 3.5 times more lipid than W _m . The amount of phosphorus was the same. Yeasts grown on methionine synthesized more ergosterol than choline-grown cells. The rate of formation of spheroplasts was higher in methionine-grown cells. Rates of incorporation of adenine, glutamic acid, and uracil were similar in cells grown on methionine or choline; incorporation of phenylalanine and tyrosine was depressed in methionine-grown cells.     

PATHWAY OF WATER MOVEMENT IN HYDROIDS OF POLYTRICHUM COMMUNE HEDW. (BRYOPSIDA)

The pathway of water movement in hydroids of Polytrichum was determined by the precipitation of an electron-dense crystal (Prussian blue) in the transpirational stream. Hydrolysed end walls appear highly water permeable since Prussian blue granules were localized within the loose fibrillar network. Electron-dense granules were found free in the lumen but not in the lateral wall or in the middle lamella. These results are compared with data from vascular plant tracheary elements.     

The release of α-amylase through gibberellin-treated barley aleurone cell walls

Localisation of -amylase (EC 3.2.1.1.) in low-temperature-embedded isolated barley (Hordeum vulgare L.) aleurone has been achieved using rhodamine-labelled secondary antibodies and the protein A-gold technique. Treatment with gibberellic acid (GA₃) resulted in an increase of immunofluorescence in the cytoplasm of aleurone cells and also its appearance in specific regions of the cell walls. Cytoplasmic label was neither perinuclear nor associated specifically with aleurone grains as had been found in earlier work, but was present throughout the cytoplasm of all cells. A relatively high level of labelling occurred in hydrolysed wall regions. Label was also associated with plasmodesmata in both hydrolysed and unhydrolysed wall regions. The pattern of labelling indicates that -amylase is released from aleurone via digested wall channels and that, except for the inner wall layer, unhydrolysed regions are impermeable to the enzyme. It is suggested that the resistant wall tubes around plasmodesmata may facilitate enzyme release by providing a pathway for transfer, especially of wall hydrolases, into the more impermeable parts of the wall.Abbreviations ER endoplasmic reticulum - GA₃ gibberellic acid - RER rough endoplasmic reticulum     

Sporangila autolysis in Clostridium perfringens type A

The autolytic system functioning in the release of mature spores and enterotoxin from sporangia of Clostridium prefringens was partially characterized. After sporangial autolysis in buffer, the supernatant fluid of the suspension contained autolysin active against purified sporangial walls. The autolysin was most active at pH 8 and 37°C, in the presence of Co²⁺ (0.3 · 10⁻³ M CoCl₂) and trypsin (48 μg/ml). Sodium dodecyl sulfate-treated sporangial walls further extracted with trichloroacetic acid to remove teichoic acid were a better enzyme substrate than walls treated only with sodium dodecyl sulfate. N-Acetylmuramyl-l-alanine amidase activity which released N-terminal alanine, and endopeptidase activity which hydrolysed the d-alanyl-glycine linkage liberating N-terminal glycine and C-terminal alanine, were both functional at pH 8. It is not known if one or two enzyme are involved. Autolysin appeared in cells as early as 2 h after inoculation into sporulation medium. Two asporogenic Stage 0 mutants grown in sporulation medium also produced autolysin identical in mode of action to that of the sporogenic wild type. Although the active cellular autolysin concentration subsequently decreased as cells sporilated, the walls of 8-h-old sporangia containing refractile heat-resistant spores were more susceptible to digestion by autolysin, than those of 2-, 4-, or 6-h-old cells grown in sporulation medium or of 4- or 14-h vegetative cells from growth medium. The results suggest that a progressive change may occur in the structure of the sporangial wall during spore morphogenesis, thus increasing its susceptibility to autolysis.     

Partial purification and properties of extracellular chitinase produced by Acremonium obclavatum,an antagonist to the groundnut rust,Puccinia arachidis

An extracellular chitinase of Acremonium obclavatum was partially purified. It had an M _r of 45 kDa on SDS-PAGE, and was optimally active at pH 3 to 4 and 50°C. Hg and Mn (10 mm) inhibited activity. The chitinase hydrolysed colloidal chitin more rapidly than crude chitin or isolated A. obclavatum cell walls. The partially-purified enzyme inhibited uredospore germination and germ-tube growth of Puccinia arachidis.The authors are with the Centre for Advanced Study in Botany, University of Madras, Guindy campus, Madras 600 025, India     

Water permeability of Betula periderm

The water permeability of periderm membranes stripped from mature trees of Betula pendula Roth was investigated. The diffusion of water was studied using the system water/membrane/water, and transpiration was measured using the system water/membrane/water vapor. Betula periderm consists of successive periderm layers each made up of about 5 heavily suberized cell layers and a varying number of cell layers that are little suberized, if at all. It is shown that these layers act as resistances in series. The permeability coefficient of the diffusion of water (P _d) can be predicted with 79% accuracy from the reciprocal of the membrane weight (x in mg cm^-2) by means of the linear equation P _d=14.69·10^-7 x-0.73·10^-7. For example, the P _d of a periderm membrane having a weight of 10 mg cm^-2 (approx. 250 m thick) is 7.4·10^-8 cm s^-1, which is comparable to the permeability of cuticles. This comparison shows that on a basis of unit thickness, Betula periderm is quite permeable to water as cuticles have the same resistance with a thickness of only 0.5 to 3 m. It is argued that this comparatively high water permeability of birch periderm is due to the fact that middle lamellae and the primary walls of periderm cells are not at all, or only incompletely suberized and, therefore, form a hydrophilic network within which the water can flow. This conclusion is based on the following observations: (1) Middle lamellae and primary walls stain strongly with toluidine blue, which shows them to be polar. (2) If silver ions are added as tracer for the flow of water, they are found only in the middle lamellae, primary walls, and in plasmodesmata, while no silver can be detected in the suberized walls. (3) Permeability coefficients of transpiration strongly depend on water activity. This shows conclusively that water flows across Betula periderm via a polar pathway. It is further argued that liquid continuity is likely to be maintained under all physiological conditions in the network formed by middle lamellae and primary walls. On the other hand, the lumina of periderm cells, intercellular air spaces in the lenticels, and even the pores in the suberized walls (remainders of plasmodesmata) will drain at a humidity of 95% and below. Due to the presence of intercellulars the permeability coefficient of lenticels is much greater than that of the periderm. A substantial amount of the total water, therefore, flows as vapor through lenticels even though they cover only 3% of the surface.Abbreviations PM perideron membrane - P _d permeability coefficient for diffusion of water - P _tt permeability coefficient of transpiration - MES (N-morpholino)ethane sulfonic acid     

Diversity in conducting cells in early land plants and comparisons with extant bryophytes

Anatomical screening using scanning electron microscopy (SEM) of short lengths of smooth coalified axes (mesofossils) from a Lochkovian (Lower Devonian) locality in the Welsh Borderland, Shropshire has revealed extensive diversity in the architecture of centrally aggregated, elongate cells. At least 14 types have been discovered, each distinguished by variation in wall architecture and combination of the cells in the central strand. End walls have not been seen. These elongate cells may have smooth, uniformly thick or thin walls, walls with smooth projections either traversing or lining the lumen, or bilayered walls, the innermost perforated by pores of plasmodesmata dimensions. The latter type may be further divided on presence or absence of projections which may line the lumen, but usually cross it and are highly disorganized. Indeed, none of the cells shows the regularity associated with the secondary thickenings of tracheids, but the imperforate/pitted forms with projections superficially resemble the S‐type tracheids of the Rhyniopsida in basic construction. Simply pitted types show greater similarity with the water‐conducting cells (WCCs) of liverworts and Takakia. To facilitate direct comparison with bryophyte conducting elements, SEM studies were undertaken on the WCCs of a number of mosses and liverworts and on the leptoids of mosses, in conjunction with a range of degradation experiments designed to assess the fossilization potential of these cells. With the exception of polytrichaceous hydroids, the latter demonstrated the resilience of hydroids and leptoids to the chemical treatments. In addition, dehydration of the leptoids produced globular residues similar to those seen in some of the fossils. This combination of techniques raises the possibility that food‐conducting cells might well be preserved in coalified fossils, and hence extends the interpretation of the functions of the elongate cells. Broadly speaking, imperforate bilayered examples may have been involved in water conduction, cells with globular residues with or without pitting involved in metabolite movement, and smooth walled examples with or without projections involved in support. The wider affinities of the plants which produced the axes remain equivocal and in the absence of sporangia it is impossible to assign them to a genus. However, this anatomical diversity in vegetative remains of extreme simplicity demonstrates far greater diversity in early land vegetation than is apparent from perusal of species lists. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141 , 297–347.     

Chemical analysis and immunolocalisation of lignin and suberin in endodermal and hypodermal/rhizodermal cell walls of developing maize (Zea mays L.) primary roots

The composition of suberin and lignin in endodermal cell walls (ECWs) and in rhizodermal/hypodermal cell walls (RHCWs) of developing primary maize (Zea mays L.) roots was analysed after depolymerisation of enzymatically isolated cell wall material. Absolute suberin amounts related to root length significantly increased from primary ECWs (Casparian strips) to secondary ECWs (suberin lamella). During further maturation of the endodermis, reaching the final tertiary developmental state characterised by the deposition of lignified secondary cell walls (u-shaped cell wall deposits), suberin amounts remained constant. Absolute amounts of lignin related to root length constantly increased throughout the change from primary to tertiary ECWs. The suberin of Casparian strips contained high amounts of carboxylic and 2-hydroxy acids, and differed substantially from the suberin of secondary and tertiary ECWs, which was dominated by high contents of ω-hydroxycarboxylic and 1,ω-dicarboxylic acids. Furthermore, the chain-length distribution of suberin monomers in primary ECWs ranged from C₁₆ to C₂₄, whereas in secondary and tertiary ECWs a shift towards higher chain lengths (C₁₆ to C₂₈) was observed. The lignin composition of Casparian strips (primary ECWs) showed a high syringyl content and was similar to lignin in secondary cell walls of the tertiary ECWs, whereas lignin in secondary ECWs contained higher amounts of p-hydroxyphenyl units. The suberin and lignin compositions of RHCWs rarely changed with increasing root age. However, compared to the suberin in ECWs, where C₁₆ and C₁₈ were the most prominent chain lengths, the suberin of RHCWs was dominated by the higher chain lengths (C₂₄ and C₂₆). The composition of RHCW lignin was similar to that of secondary-ECW lignin. Using lignin-specific antibodies, lignin epitopes were indeed found to be located in the Casparian strip. Surprisingly, the mature suberin layers of tertiary ECWs contained comparable amounts of lignin-like epitopes. Received: 19 August 1998 / Accepted: 3 February 1999     

Structure and distribution of lignin in primary and secondary cell walls of maize coleoptiles analyzed by chemical and immunological probes

Lignin is an integral constituent of the primary cell walls of the dark-grown maize (Zea mays L.) coleoptile, a juvenile organ that is still in the developmental state of rapid cell extension. Coleoptile lignin was characterized by (i) conversion to lignothiolglycolate derivative, (ii) isolation of polymeric fragments after alkaline hydrolysis, (iii) reactivity to antibodies against dehydrogenative polymers prepared from monolignols, and (iv) identification of thioacidolysis products typical of lignins. Substantial amounts of lignin could be solubilized from the coleoptile cell walls by mild alkali treatments. Thioacidolysis analyses of cell walls from coleoptiles and various mesocotyl tissues demonstrated the presence of guaiacyl-, syringyl- and (traces of)p-hydroxyphenyl units besidesp-coumaric and ferulic acids. There are tissue-specific differences in amount and composition of lignins from different parts of the maize seedling. Electron-microscopic immunogold labeling of epitopes recognized by a specific anti-guaiacyl/syringyl antibody demonstrated the presence of lignin in all cell walls of the 4-d-old coleoptile. The primary walls of parenchyma and epidermis were more weakly labeled than the secondary wall thickenings of tracheary elements. No label was found in middle lamellae and cell corners. Lignin epitopes appeared first in the tracheary elements on day 2 and in the parenchyma on day 3 after sowing. Incubation of coleoptile segments in H₂O₂ increased the amount of extractable lignin and the abundance of lignin epitopes in the parenchyma cell walls. Lignin deposition was temporally and spatially correlated with the appearance of epitopes for prolinerich proteins, but not for hydroxyproline-rich proteins, in the cell walls. The lignin content of coleoptiles was increased by irradiating the seedlings with white or farred light, correlated with the inhibition of elongation growth, while growth promotion by auxin had no effect. It is concluded that wall stiffness, and thus extension growth, of the coleoptile can be controlled by lignification of the primary cell walls. Primary-wall lignin may represent part of an extended polysaccharide-polyphenol network that limits the extensibility of the cell walls.Abbreviations G, S, H guaiacyl, syringyl andp-hydroxyphenyl constituents of lignin - HRGP hydroxyproline-rich glycoprotein - LTGA lignothioglycolic acid - PRP proline-rich protein Dedicated to Professor Benno Parthier on occasion of his 65th birthdayDeceased 7 November 1996     

Biochemical characterization of a new type of intracellular PHB depolymerase from Rhodospirillum rubrum with high hydrolytic activity on native PHB granules

A Rhodospirillum rubrum gene that is predicted to code for an extracellular poly(3-hydroxybutyrate) (PHB) depolymerase by the recently published polyhydroxyalkanoates (PHA) depolymerase engineering database was cloned. The gene product (PhaZ3 _Rru ) was expressed in recombinant E. coli, purified and biochemically characterized. PhaZ3 _Rru turned out, however, to share characteristics of intracellular PHB depolymerases and revealed a combination of properties that have not yet been described for other PHB depolymerases. A fusion of PhaZ3 _Rru with the enhanced cyan fluorescent protein was able to bind to PHB granules in vivo and supported the function as an intracellular PHB depolymerase. Purified PhaZ3 _Rru was specific for short-chain-length polyhydroxyalkanoates (PHA_SCL) and hydrolysed both untreated native PHB granules as well as trypsin-activated native PHB granules to a mixture of mono- and dimeric 3-hydroxybutyrate. Crystalline (denatured) PHB granules were not hydrolysed by PhayZ3 _Rru . Low concentrations of calcium or magnesium ions (1–5 mM) reversibly (EDTA) inhibited the enzyme. Our data suggest that PhaZ3 _Rru is the representative of a new type of the growing number of intracellular PHB depolymerases.     

Diguanidinobutanase of Pseudomonas putida and enzymatic preparation of agmatine from 1,4-diguanidinobutane

Diguanidinobutanase (EC 3.5.3.20), which catalyses the hydrolysis of 1,4-diguanidinobutane (DGB) to agmatine (1-amino-4-guanidinobutane) and urea, was purified to homogeneity from Pseudomonas putida ATCC 12633. The enzyme had a molecular mass of 170 kDa and was suggested to be a tetramer of subunits that had a molecular mass of 38 kDa. The enzyme contained two Mn²⁺ ions per subunit. DGB was the most effective substrate and its K _m was 0.65 mM. The turnover number for the subunit at saturation with DGB was 1330 molecules s^–1. The higher homologues of DGB with five to seven methylene groups were also hydrolysed effectively. Agmatine was hydrolysed at a rate of 0.6% of that observed with DGB. The agmatine homologues with five to seven methylene groups were hydrolysed, although the rates were low. The enzyme was sensitive to p-chloromercuribenzoate. Agmatine sulphate was enzymatically prepared from DGB. The purified product, free from detectable putrescine and DGB, was obtained with a yield of 93% (mol/mol).Student of the United Graduate School of Agricultural Sciences, Gifu University     

The localization of galactosyl residues and lectin receptors in the mucilage and the cell walls ofCosmocladium saxonicum (Desmidiaceae) by means of fluorescent probes

Summary The localization of galactosyl residues and lectin binding sites in mucilage and cell walls of the colony forming green algaCosmocladium saxonicum (Desmidiaceae) has been studied using fluorescent probes. In mucilaginous filaments, which are secreted through pores of the cell wall, and in the primary cell wall galactosyl residues in -bound configuration are exposed, as indicated by indirect immunofluorescence using antiserum to monogalactosyl diglyceride residues. Concanavalin A receptors are present mainly at the surface of the secondary cell wall, whereasRicinus communis agglutinin, type I, receptors are predominantly associated with mucilaginous connecting strands, which join adjacent cells within a colony. NoUlex europaeus agglutinin receptors were found. Application of the fluorochrome calcofluor white ST resulted in labeling both, the primary and the secondary cell wall. The data, obtained with the fluorescent probes were compared with those obtained by thin layer chromatography of hydrolysed mucilage.This work includes parts of a doctoral thesis of B. S. carried out under the supervision of Prof. Dr. M.Mix.     

Purification and Properties of a Type II-like Dipeptidyl Peptidase from the Ruminal Peptidolytic Bacterium,Prevotella albensis M384

A dipeptidyl peptidase which hydrolyses the synthetic dipeptidyl peptidase (DPP) substrate, Ala₂- p -nitroanilide, was purified 193-fold from the ruminal peptidolytic bacterium, Prevotella albensis M384. The enzyme was a homodimer of molecular mass 91 kDa. Its activity against Ala₂- p -nitroanilide had optimal pH and temperature of 7.2 and 40°C respectively. Enzyme activity was inhibited by the serine protease inhibitors, PMSF and dichloroisocoumarin, but not by inhibitors of other categories of proteases. Synthetic substrates for DPP-1 (GlyArg- p -nitroanilide, GlyArg-4-methoxy-naphthylamide), DPP-3 (ArgArg-4-methoxynaphthylamide) and DPP-4 (GlyPro-4-methoxynaphthylamide) or for leucine or alanine aminopeptidase were not hydrolysed, nor were di- or tripeptides. N-Acetyl-Ala₂- p -nitroanilide was not hydrolysed. Oligopeptides with Ala, Ile, Ser or Val adjacent to the N-terminal amino acid were all hydrolysed, while peptides with basic or acidic residues in the same position were not. The purified DPP from P. albensis is therefore most similar in its catalytic properties to mammalian DPP-2.     

Potential antifouling strategies for marine finfish aquaculture: the effects of physical and chemical treatments on the settlement and survival of the hydroid Ectopleura larynx

The hydroid Ectopleura larynx is a common fouling organism on aquaculture nets. To contribute to the development of novel cleaning methods, laboratory and field studies determined the effects of heat (30, 40, 50 and 60°C for immersion times of 1 and 3 s) and acetic acid (0.2 and 2.0% for immersion times of 1, 3 and 10 s, 1 and 5 min) on the settlement of actinulae and the survival of juvenile and adult E. larynx. Laboratory studies showed that, regardless of immersion time, a temperature of 50°C was effective in preventing the settlement of actinulae and the survival of juveniles, while ≤12% of adult hydroids could survive. A temperature of 60°C killed all adult hydroids. For an acetic acid concentration of 0.2%, an immersion time of 1 min substantially reduced the settlement of actinulae and the survival of juvenile and adult hydroids, and none of the juvenile and adult hydroids survived after 5 min. For an acetic acid concentration of 2.0%, all immersion times were effective and reduced the mean settlement of actinulae and the survival of juvenile and adult hydroids to ≤10%. Field studies with fouled net panels exposed to selected heat or acetic acid treatments showed small reductions in mean wet weight and net aperture occlusion of the net panels 2 and 5 days after treatment. Visual inspections of the net panels showed that hydranths of the hydroids were shed, but the dead stolons of the hydroids remained on the treated net panels. Novel cleaning methods and devices may utilise these results to effectively kill E. larynx on aquaculture nets, while further studies are needed to determine the necessity of removing the dead hydroids before further biofouling accumulates on thenets.     

Cell wall polysaccharides from cell suspension cultures of the Atlantic Forest tree Rudgea jasminoides (Rubiaceae)

Rudgea jasminoides (Rubiaceae) is a tropical tree species native of the Atlantic Forest in the south of Brazil. Previous studies with leaf cell walls of R. jasminoides showed a different proportion of cross-linked glycans compared to what is usually reported for eudicots. However, due to the difficulties of working with whole plant organs, cell suspensions of R. jasminoides, consisting of predominantly undifferentiated cells with mainly primary cell walls, were used to examine cell walls and extracellular soluble polysaccharides (EP) released into the culture medium. Sugar composition and linkage analysis showed homogalacturonans, xylogalacturonans and arabinogalactans to be the predominant EP. In the cell wall, homogalacturonans and arabinogalactans are the major pectins, and xyloglucans and xylans are the major cross-linking glycans. The presence of xylogalacturonans in the R. jasminoides cell cultures seems to be related to the occurrence of a homogeneous cell suspension with loosely attached cells. Although all alkali extractions from the cell walls yielded amounts of xyloglucan that exceed those of the xylans, the latter was found in a proportion that is higher than what has been usually reported for primary cell walls of most eudicots. The xyloglucan from cell walls of cell suspension cultures of R. jasminoides has low fucosylation levels and high proportion of galactosyl residues, a branching pattern commonly found in storage cell-wall xyloglucans.     

The genusCandida berkhout

The aim of the study was to verify the accuracy of the taxonomic classification of rough variants of the speciesCandida guilliermondii on the basis of comprehensive study of phenetic manifestation and to determine differences in cell wall structure with special reference to polysaccharides (1) According to their phenotype, the test strainsCandida guilliermondii (Cast.) Langeron et Guerra andCandida guilliermondii var.membranaefaciens Lodder et Kreger-Van Rij belong to the speciesCandida guilliermondii, whileCandida guilliermondii var.nitratophila Diddens et Lodder is phenotypically closer toCandida pelliculosa. (2) Observation of native and hydrolysed cell walls in the electron microscope showed no differences between the test strains. (3) The results of X-ray phase analysis of cell walls differentiatedCandida guilliermondii var.nitratophila from the other two, however. (4) Electron microscopy photomicrographs and diffractograms of cell walls indicated that, after 2% HCl extraction at 100 C, the cell walls contain chitin, which is isolated by further extraction with 30% HCl. After 3% NaOH hydrolysis the chitin diffractogram is not clear.