Rapid detection ofRhizoctonia species, causal agents of rice sheath diseases, by PCR-RFLP analysis using an alkaline DNA extraction method

Restriction fragment length polymorphism (RFLP) analysis for DNA products amplified by the polymerase chain reaction (PCR) was used for the direct detection ofRhizoctonia solani AG 1 IA and AG 2-2 IIIB,R. oryzae, R. oryzae-sativae andR. fumigata from the diseased rice sheaths. A rapid DNA extraction method with a solution of sodium hydroxide was conducted to extract parasite DNA from diseased rice sheaths. 28S ribosomal DNA (rDNA) derived from fungal genomic DNA extracted by the alkaline method was specifically PCR-amplified. The results of PCR-RFLP analysis for DNA samples from artificially inoculated rice sheath tissues with eachRhizoctonia spp. and the corresponding culture on the medium using two restriction enzymes.HhaI andMspI, showed identical polymorphisms. PCR-RFLP analysis using DNA samples from naturally infected rice sheath tissues also revealed the possibility of direct diagnosis ofR. solani AG 1 IA,R. oryzae andR. oryzae-sativae.     

Contribution of basal portion of shoot to N2 fixation associated with wetland rice

Summary Oryza sativa grown in flooded soil were transferred to water culture solution and acetylene reduction activities (ARA) of intact plants and rootless plants were measured for 5 h. Relative rate of ARA associated with the rootless wetland rice plant as compared with an intact plant varied from 8 to 100 percent, depending on the growth stage and varieties of rice and highest at the early stage (3 weeks after transplanting) for all varieties tested (IR26, Latisail, Khao Lo, and JBS236). ARA of shoots was associated with basal parts of the shoots about 3 cm from the base of wetland cultivated rice andOryza australiensis. Phyllospheric ARA was negligible except for senescent outer leaf sheaths. Microaerophilic N₂-fixing bacteria also inhabited basal parts of shoots (outer leaf sheaths and stems) of wetland rice. These findings suggest that N₂-fixation is partly associated with the shoots of wetland rice plants.     

Mycorrhizae in Adenostoma fasciculatum Hook. & Arn.: a combination of unusual ecto- and endo-forms

 The mycorrhizal status of Adenostoma fasciculatum, the dominant shrub in California chaparral, has been unclear. In two typical, nearly monospecificstands, A. fasciculatum was found to have arbuscules and intercellular hyphae. Antisera detected hyphae of the arbuscular mycorrhizal (AM) fungal genera Acaulospora, Glomus, and Scutellospora, although we found only spores of Glomus. Some roots had partial sheaths and inter- and intracellular septate fungi without indications of root necrosis. Ectomycorrhizal root tips were also found, including Cenococcum and other unknown taxa. Sporocarps of EM fungi including species of Rhizopogon, Pisolithus, Balsamia, Laccaria, Hygrophorus, and Cortinarius were found in the stand, with no other EM or arbutoid mycorrhizal plants nearby. These observations indicate that A. fasciculatum forms mycorrhizae with AM, septate, and EM fungi, but often fails to form easily recognizable mycorrhizal structures. Accepted: 5 September 1998     

Culturable bacterial communities on leaf sheaths and panicles of rice plants in Japan

Culturable bacterial communities on rice plants were investigated from 2001 to 2003. In total, 1,394 bacterial isolates were obtained from the uppermost leaf sheaths at 1 month before heading time and from leaf sheaths and panicles at heading time. The average culturable bacterial population on the leaf sheaths was larger at heading time than at 1 month previously. Furthermore, the population was significantly larger on panicles than on leaf sheaths, suggesting that the bacterial population is influenced by the organs of rice plants. Larger proportions of bacteria were obtained from the macerates of leaf sheaths after washing with phosphate buffer, and most culturable bacteria were verified to inhabit the inside or inner surface, rather than the outer surface, of the tissues. Verification of the bacterial composition based on 16S rRNA gene sequences revealed that genera of Sphingomonas, Microbacterium, Methylobacterium, and Acidovorax tended to be dominant colonizers on leaf sheaths, whereas Pseudomonas and Pantoea were isolated mainly from the panicles, indicating that leaf sheaths and panicles harbor distinct communities. Furthermore, the richness of bacterial genera was less on both leaf sheaths and panicles at heading time compared with that observed 1 month before heading time. Phylogenetic analyses using bacterial isolates belonging to the four dominant genera inhabiting leaf sheaths at heading time revealed that particular bacterial groups in each genus colonized the leaf sheaths.     

Fluvival tufa formation in a hard-water creek (Deinschwanger Bach, Franconian Alb, Germany)

Summary Cyanobacteria-dominated biofilms involved in tufa deposition in the hardwater creek Deinschwanger Bach, Bavaria, were investigated with regard to their effect on the carbonate equilibrium and fabric formation. Current tufa deposition is evident by up to 1.5 mm thick crusts that have formed on substrate plates placed in the creek for 10 months. Hydrochemistry data indicate that carbonate precipitation along the creek is physicochemically driven by CO₂ degassing, whereas photosynthetic carbon assimilation is without detectable effect on the macroscale carbonate equilibrium. However, stable isotope data indicate a minor photosynthetic effect, but only for the lower creek section where the pCO₂ already drops to the two-fold of the atmospheric level. Though the initial process of external nucleation on cyanobacterial sheaths in the lower creck section might be promoted of by a photosynthetically-induced microscale pH gradient, the effect is not strong enough to cause a CaCO₃ impregnation of the sheaths. The fabric of the laminated tufa crusts in the creek reflects the temporal alternation of porous microspariticPhormidium incrustatum-Phormidium foveolarum-diatom biofilms in spring, micrite-impregnatedPhormidium incrustatum-Phormidium foveolarum-diatom biofilms in summerautumn, and detritus-rich non-calcified diatom-biofilms in winter. By contrast, exopolymer-poor surfaces of cascade tufa mosses show large, euhedral spar crystals. Non-phototrophic bacteria, which occur in large numbers inPhormidium incrustatum-Phormidium foveolarums-diatom-communities, thrive on extracellular polymeric substances (EPS) and dead cells of the cyanobacteria and are unlikely to promote CaCO₃ precipitation.     

Formation of Gold Particles via Thiol Groups on Glycoconjugates Comprising the Sheath Skeleton of Leptothrix

Leptothrix, iron-oxidizing bacterium, produces microtubular sheaths that surround the catenulate cells. Organic nanofibrils excreted from the cell surfaces interweave and coalesce to form immature sheaths, which attract aqueous-phase inorganics to eventually form mature organic–inorganic sheaths. Such inorganic encrustation of the sheaths results from interactions between functional groups in the sheath skeleton and inorganics. Based on our previous findings that Leptothrix sheath skeleton sorbed 47 inorganics (Au was one of the most abundant adsorbates), we examined the sorption status of Au cations on cell-enclosing sheaths and their protein-free remnants and found that nano to sub-micron Au particles (AuNPs and AuSMPs, respectively) formed on the sheath-forming polymer consisting of a glycoconjugate (an amphoteric glycan modified with cysteine, glycine, and 3-hydroxypropionic acid). When the purified polymer was incubated in HAuCl₄ solution, AuNPs and AuSMPs formed on the polymer surfaces. Both particles formed also on cell-enclosing sheaths and protein-free sheath remnants incubated in HAuCl₄ solution. When SH groups in the cell-enclosing sheaths were masked with a fluorescent protein, Au particles did not form after incubation in HAuCl₄ solution. Results implicate that SH groups are at least partially involved in the reduction of Au cations to metallic Au and eventual formation of Au particles.     

Occurrence of the suberized lamella in leaves of grasses of different photosynthetic types. I. In parenchymatous bundle sheaths and PCR (“Kranz”) sheaths

Summary Leaf blades of 42 grasses (Poaceae) have been examined ultrastructurally for the occurrence of a suberized lamella in walls of parenchymatous bundle sheaths and PCR (= Kranz) sheaths in both large and small vascular bundles. The sample includes species from a range of major grass taxa, and represents all photosynthetic types found in the grasses. Three grasses with unusual C₄ leaf anatomy were also included:Alloteropsis semialata, Aristida biglandulosa, Arundinella nepalensis. The presence of a suberized lamella in PCR cell walls was perfectly correlated with photosynthetic type. All PEP-carboxykinase type and NADP-malic enzyme type C₄ species examined possessed a suberized lamella in outer tangential and radial walls, but with variable presence in inner tangential walls. PCR cells of bothAlloteropsis semialata andArundinella nepalensis also possessed a suberized lamella. A lamella was totally absent from parenchymatous bundle sheath cells of the C₃ species examined (5 spp.) and ofPanicum milioides, a C₃-C₄ intermediate. It was also absent from PCR cells of NAD-malic enzyme type C₄ species (14 spp.) andAristida biglandulosa. The results are discussed in relation to the leakage of CO₂ from PCR cells, and to differences between C₄ types in ¹³C values, chloroplast position in PCR cells, and other anatomical characteristics.     

Investigations on theSphaerotilus-Leptothrix group

Thirty-fourSphaerotilus andLeptothrix strains were isolated from sewage, activated sludge and iron-containing ditch- and well-water, and their morphological and physiological characters studied. The organisms were grown under different conditions, e.g. on peptoneglucose agar and yeast-extract-manganous-carbonate agar, and in running ditch-water containing ferrous iron. Growth of these bacteria in synthetic media, with glucose as carbon source and aspartic and glutamic acids or inorganic nitrogen compounds as nitrogen source, required added vitamin B₁₂ unless nitrogen was supplied as hydrolyzed casein or as a mixture ofl-amino acids. Methionine was found to be responsible for this replacement of vitamin B₁₂.Five different types of sheath-forming bacteria were distinguished in the present study. Type I is the typical sewage organismSphaerotilus natans. It has large cells, grows well with relatively high concentrations of organic substrates, but cannot oxidize manganous compounds. In running ditch-water containing ferrous iron, ferric hydroxide may be deposited in and on its sheaths. AlthoughS. natans under such conditions may resemble the iron bacteriumLeptothrix ochracea, it has relatively long sheaths, partly filled with cells in contrast with the short and mostly empty sheaths of the latter.S. natans could be readily reisolated from its iron-bacterium cultures but very seldom from crude cultures ofL. ochracea; thus the two organisms are clearly different. Types II and III have relatively large cells, respond poorly to organic nutrients, but are able to oxidize manganous compounds. Type II forms fungus-like flocks in liquid media and resembles microscopicallyL. lopholea, with which it may be identical. Type III resemblesL. ochracea more closely than does any other type, but is probably not identical with it; the nameL. pseudo-ochracea sp.n. is proposed for this type. Type IV is intermediate between types I and V. In media with relatively high concentrations of organic nutrients it behaves like a sewage organism, but in poor media containing ferrous and manganous compounds, it behaves like an iron bacterium, depositing large amounts of ferric and manganic oxides in and on its sheaths; for this type the nameL. cholodnii sp.n. is proposed. Type V has small cells, grows poorly in all media tested, but actively oxidizes manganous compounds; the nameLeptothrix discophora is reserved for this type.The globular inclusions in the cells ofS. natans and other members of theSphaerotilus-Leptothrix group consist of poly--hydroxybutyrate.     

The Mechanical Roles of Clasping Leaf Sheaths: Evidence fromArundinaria tecta(Poaceae) Shoots Subjected to Bending and Twisting Forces

Representative shoot segments of the grass speciesArundinariatéctaconsisting of one intact internode and its subtendingnode and clasping leaf sheath were tested to determine the mechanicalinfluence of the leaf sheath on the ability of stems to resistbending and twisting forces. These segments were also used tomeasure shoot morphometry and composite tissue Young's and shearmoduli (EandG,respectively) to simulate the global deformationpatterns attending bending and twisting by means of finite elementanalyses. On average, leaf sheaths contributed 33% of the overallbending stiffness and 43% of the overall torsional stiffnessof stem segments. Comparisons betweenEandGof isolated internodesand leaf sheaths indicated that sheaths were composed of stiffertissues measured either in bending or twisting. Thus, leaf sheathscould act as an external cylindrical brace composed of stiffermaterials than those of the internodes they enveloped. The magnitudesof internodalEandGwere correlated with internodal shape suchthat the ability of internodes to resist twisting relative tothe ability to resist bending forces decreased as internodesbecame more slender or developed thinner walls (both of whichoccur in an acropetal direction from the base to the tip ofshoots). Finite element simulations predicted that, in bending,the leaf sheath laterally braces internodal walls as they tendto ovalize in cross section and push against its inner surfacewhich ovalizes to a lesser extent in the plane normal to thecurvature of shoot flexure. In twisting, the successive ovalizedtransections of internodal walls assumed a helical pattern alongthe length of shoot segments. This helical deformation patternwas attended by an inner lateral contraction of internodal wallsthat was less developed in the leaf sheath that thus provideddecreasing mechanical support to the internode as the lateralcontraction of internodal walls amplified. The twisting of internodesand sheaths was also predicted to concentrate tensile and shearstrains in the nodal diaphragm. Here stress intensities sufficientto produce tissue shear failure were concentrated at two opposingpoints on the surface of the diaphragm. Finite element analysesthus identified a potential weak point in the mechanical constructionof hollow, septate shoots that are, nevertheless, more thanadequately stiff to support their own weight, yet sufficientlyflexible to twist without irreparable damage in normal winds.Copyright1998 Annals of Botany Company Plant stems; nodes; internodes; leaf sheaths; elastic moduli; wind lodging; biomechanics.     

Ultrastructural aspects of leaves inFestuca ovina andPoa sphondylodes (C-3 Poaceae)

Structural aspects of the leaves of two common festucoids,Festuca ovina andPoa sphondylodes, have been examined employing the electron microscopy. The nature of vascular bundles and of sheaths that surround vascular tissues was discussed in the study. The festucoids exhibited a non-Kranz C-3 anatomy with more than four mesophyll cells separating the bundle sheaths of a leaf blade. Vascular tissues in theseFestuca andPoa leaves were surrounded by a double sheath: an inner distinct mestome sheath (MST) and an outer indistinctive layer of parenchymatous bundle sheath (PBS) cells. The PBS cells were much larger than the MST and had thin walls. The MST cells were relatively small and rectangular inP. sphondylodes and more or less hexangular in transverse sections ofF. ovina. InP. sphondylodes, MST had conspicuously thickened inner tangential walls with asymmetrically uninterrupted suberized lamellae in radial and tangential walls. In most differentiated MST cells, all walls were highly suberized. During suberin deposition, MST cells were quite vacuolated and most of the cytoplasm was present as a thin peripheral layer. However, MST walls inF. ovina revealed very thin suberized lamellae with translucent striations. No chloroplasts were detected inP. sphondylodes, whereas the MST inF. ovina contained small chloroplasts. Plasmodesmata were well developed in the primary pit fields of walls between MST and vascular cells, and between adjacent MST cells. Plasmodesmata were less frequent in the walls between the inner and outer sheath cells. Suberized lamellae were totally absent from the PBS cell walls in all veins. External to the PBS, the mesophyll comprised thin walled cells with abundant intercellular spaces. Peripherally arranged chloroplasts in the mesophyll were numerous and often larger than those of PBS and MST cells. Characteristics associated with C-3 and other ultrastructural features were also discussed in the study.     

C4 syndrome of the species in theDichotomiflora group of the genusPanicum (Gramineae)

Leaf anatomy, pattern of post-illumination CO₂ burst (PIB) and activity of three C₄-acid decarboxylating enzymes in C₄ photosynthesis were investigated with the leaves of five species in theDichotomiflora group of the genusPanicum. All species had mestome sheaths, exhibited the sharp pattern of PIB in less than 30 sec of darkness and were classified as NAD-malie enzyme species biochemically. However, they clearly fell into two groups according to the difference in chloroplast location in bundle sheath cells (BSC).P. coloratum var.makarikariense, P. lanipes andP. stapfianum had centripetal chloroplasts, whereasP. laevifolium andP. longijubatum had centrifugal chloroplasts, whereas cv. Kabulabula and cv. Solai had centrifugal chlorplasts. The results indicate that theDichotomiflora group had the two leaf anatomical variations of NAD-malic enzyme species. In addition, the results onP. coloratum suggest that this species may be divided into two separate species by chloroplast location in BSC. The ultrastructural features of leaves ofP. dichtomiflorum, NAD-malic enzyme species with centrifugal chloroplasts, were also investigated. Chloroplasts in BSC had well-developed grana, and numerous large mitochondria with extensively developed internal membrane structure were restricted to the area between the chloroplsts and the vacuole in BSC.     

Enzymatic studies of the extracellular mucilage of two aquatic hyphomycetes,Lemonniera aquatica andMycocentrospora filiformis

The effect of three carbohydrate-digesting enzymes, β-glucuronidase, lyticase and α-mannosidase and three proteolytic enzymes, α-chymotrypsin, papain and pronase E, on the strength of conidial attachment ofLemonniera aquatica andMycoentrospora filiformis was determined using the LH_Fowler cell Adhesion Measurement Module. Carbohydrate-digesting enzyme treatments showed significant differences in number of attached and detached, conidia versus control samples; little or no effect was observed for the proteolytic enzymes. Scanning and transmission electron microscopy showed different degrees of mucilage digestion by the carbohydrate-digesting enzymes on the germ hyphae, hyphae subtending appressoria, and appressoria of the two species. The loss of mucilage integrity and decrease in mucilage thickness were more pronounced on the hyphal sheaths than on the appressorial sheaths. Lyticase caused the most severe damage to the mucilage and cytoplasm of both fungi, particularlyL. aquatica. β-Glucuronidase and α-mannosidase exhibited more effective mucilage digestion onM. filiformis than onL. aquatica. Results indicate that the mucilage of the two species is mainly polysaccharide, containing more β-1,3-glucans than β-glucuronide and α-mannosyl residues. Variability of mucilage composition exists between these species and also between different structures of the same fungus.     

Selection of plant parts by Depressaria multifidae (Lep., Oecophoridae) on its seasonally-restricted hostplant, Lomatium grayi (Umbelliferae)

ABSTRACT.

• 1 Depressaria multifidae Clarke feeds on a broader variety of Umbelliferae plant parts than other Depressaria species.
• 2 Early instar larvae feed in the sheaths surrounding floral buds and leaves. Later instar larvae feed in the sheaths and floral stems and on flowers and leaves.
• 3 Floral stems bored by larvae had significantly larger basal stem diameters than floral stems that were not bored. Smaller stems usually have umbels with only male flowers, and wither after flowering, too soon for larvae to complete development. In contrast, larger stems often have umbels with some hermaphroditic flowers, which remain green and erect long enough for larvae to complete development. Hence, selection may favour larvae that bore only in relatively large stems.
• 4 In the laboratory, larvae fed sheaths with enclosed floral buds, flowers, or leaves all pupated at the same weight, but larvae fed floral stems pupated at a significantly lower weight. Larval and pupal development time was the same on all plant parts.
• 5 In the field, larvae restricted to a single umbel throughout development pupated at the same weight as those restricted to a single leaf.
• 6 Unlike in other Depressaria species, nitrogen levels only partly correspond to the pattern of use of plant parts in D.multifidae. Nitrogen values varied as follows: floral buds > immature leaves ≥ flowers > floral stalks > sheaths excluding floral buds or leaves.
• 7 The broad variety of plant parts used by D.multifidae may result partly from the problem of feeding on a small, seasonally restricted hostplant; the greater use of sheaths and floral stems than in other Depressaria species may result from selection for safety from parasites or predators.
• 8 The results for D.multifidae indicate that the way in which an insect feeds on a plant species can vary broadly even at a single site.

     

Comparison of the role of the foliar sheath in nutrient (ammonium and phosphate) acquisition by the seagrass <Emphasis Type="Italic">Thalassia hemprichii</Emphasis> (Ehrenb.) Aschers. at two different sites on tropical Hainan Island,China

Generally, the foliar sheaths of seagrass contribute a large biomass to the dry weight of plants, and are found to be above-sediment biomass or, sometimes, below-sediment biomass. However, the role of foliar sheaths of seagrass in nutrient uptake has not yet been established. Thus, this study was performed to test whether the growth form of foliar sheaths affects the nutrient uptake properties of the seagrass. Two separate sets of morphotypes of the seagrass Thalassia hemprichii were collected from two different tropical meadows in coastal Hainan Island, China in the South China Sea. Ammonium (NH₄ ⁺) and phosphate (P_i) uptake by solely blades and roots (experiment I), and above and below-sediment tissues (experiment II) of the two sets of specimens were examined in partitioned chambers using laboratory incubations. Curve profiles of the blade and root saturation uptake kinetics were shown to be similar for the two morphotypes of T. hemprichii. However, the above and below-sediment tissues uptake kinetics had different characteristics between the two morphotypes. For plants with above-sediment foliar sheaths, uptake by the above-sediment tissues contributed an important part of the whole plants’ nutrient acquisition. In contrast, for plants with below-sediment foliar sheaths, the contribution of nutrient uptake by above-sediment foliar blade tissues seemed almost negligible. Therefore, the results demonstrated that foliar sheaths of the tropical seagrass T. hemprichii were able to absorb NH₄ ⁺ and P_i. Especially interesting is that the capacity for uptake by robust foliar sheaths growing beneath the sediment was remarkable (we termed this the Zhang–Huang–Thorhaug effect). The role of sheaths in nutrient acquisition found in this study is critical in elucidating seagrass nutrient uptake strategies.     

Morphological classification of ectomycorrhizas ofPinus densiflora

Morphological classification of ectomycorrhizas ofPinus densiflora was conducted. Fifty soil samples containing pine ectomycorrhizas, and 40 pine seedlings were collected randomly in two separate reforested stands ofP. densiflora (45 yr old) from May 1992 to October 1994. Fifty-six types of ectomycorrhizas could be classified based upon microscopically observable morphological characteristics. Fifty percent of the types showed cystidia or other specific characteristics such as laticiferous hyphae in the fungal sheaths, verrucose emanating hyphae and a positive hyphal reaction to UV irradiation. Four mycorrhizal types were confirmed to be formed by the fungiRussula delica, R. mariae, R. nigricans, andCenococcum geophilum, respectively. Although the other 52 types were unidentified mycobionts at species level, it was inferred that they were formed by the fungiHebeloma, Lactarius, Russula andTuber. There was a slight difference in the observed mycorrhizal types between the tree ages. Contribution No. 127, Laboratories of Plant Pathology and Mycology, Institute of Agriculture and Forestry, University of Tsukuba.     

Leafhoppers on leaves: An analysis of feeding behavior using conditional probabilities

Feeding behavior of four deltocephaline leafhoppers,Graminella nigrifrons, G. oquaka, Amblysellus grex, andDalbulus maidis on maize and johnsongrass was analyzed using an electronic monitoring device. Five distinct waveform patterns were identified: secretion of sheath saliva (salivation), nonvascular probing, nonsieve element ingestion, x-waveform, and phloem ingestion. Waveforms were associated with feeding activities by correlation with light microscopic examination of salivary sheath termination points in leaf tissue and analysis of honeydew excreted by monitored leafhoppers. In previous studies x-waveforms have been reported to occur only when the stylets of homopterans are in contact with the phloem; the function of x-waveforms is poorly understood. There were no differences in time spent salivating or ingesting from nonsieve elements amongG. nigrifrons, G. oquaka andA. grex on either plant.D. maidis differed from other species in phloem probing and feeding behavior; only a small proportion produced x-waveforms, although those that did spent significantly more time in this behavior than other species. Also,D. maidis spent more time than other leafhoppers ingesting from tissues other than sieve elements. Kinetic diagrams of transition probabilities show that probing activities of all species were not random regarding the sequence of behaviors culminating in phloem ingestion. Thirty-five percent ofG. nigrifrons x-waveforms were followed by nonsieve element ingestion. This was consistent with observations showing that salivary sheaths of leafhoppers producing x-waveforms sometimes do not terminate in the phloem, but rather in nearby cells. Phloem ingestion was always preceeded by x-waveforms. The quantitative differences in probing behavior are discussed in relation to ability of these leafhoppers to transmit the phloem-associated maize chlorotic dwarf waikavirus.     

Site-specific structural analysis of a yeast prion strain with species-specific seeding activity

Prion proteins misfold and aggregate into multiple infectious strain variants that possess unique abilities to overcome prion species barriers, yet the structural basis for the species-specific infectivities of prion strains is poorly understood. Therefore, we have investigated the site-specific structural properties of a promiscuous chimeric form of the yeast prion Sup35 from Saccharomyces cerevisiae and Candida albicans. The Sup35 chimera forms two strain variants, each of which selectively infect one species but not the other. Importantly, the N-terminal and middle domains of the Sup35 chimera (collectively referred to as Sup35NM) contain two prion recognition elements (one from each species) that regulate the nucleation of each strain. Mutations in either prion recognition element significantly bias nucleation of one strain conformation relative to the other. Herein, we have investigated the folding of each prion recognition element for the serine-to-arginine mutant at residue 17 of Sup35NM chimera known to promote nucleation of C. albicans strain conformation. Using cysteine-specific labeling analysis, we find that residues in the C. albicans prion recognition element are solvent-shielded, while those outside the recognition sequence (including most of those in the S. cerevisiae recognition element) are solvent-exposed. Moreover, we find that proline mutations in the C. albicans recognition sequence disrupt the prion templating activity of this strain conformation. Our structural findings reveal that differential folding of complementary and non-complementary prion recognition elements within the prion amyloid core of the Sup35NM chimera is the structural basis for its species-specific templating activity.     

Phylogenetic and taxonomic problems in freshwater Oligochaeta with special emphasis on chitinous structures in Tubificinae

Setae and chitinous penis sheaths are the main characters used to distinguish genera and species of the subfamily Tubificinae. Genital setae and penis sheaths are of functional importance to facilitate copulation. Similar structures in different genera may be homologous or products of parallel evolution (homoiologous). Form and dimensions of the penis sheaths of many tubificine species are very variable. Transspecific overlap of quantitative species characters can make the determination of specimens in the genus Limnodrilus difficult. The configuration of the distal ends of the penis sheaths is an important character to distinguish Limnodrilus species. The definition of the intraspecific variability of this morphological character is problematic.     

The In Vitro Self-Assembly of Supramolecular Structures after the Spontaneous Disassembly of Carotovoricins

The self-assembly of supramolecular structures (empty sheaths and polysheaths of the macromolecular Erwinia carotovora bacteriocins) was studied by electron microscopy in the course of 1- to 2-year incubation of phage particles at 4°C. This study showed that the empty sheaths and polysheaths of the bacteriocins of eight E. carotovora strains spontaneously assemble at the self-assembly centers (or crystallization centers), which have a diameter of 26–65 nm and contain a dense proteinaceous material. The self-assembly center consists of two components, a primer and the structural protein of contracted sheaths. Empty sheaths assembled in the crystallization centers are polar structures synthesized through the stepwise head-to-tail polymerization of monomeric units. The supramolecular structures of two E. carotovora 62A bacteriocins are assembled in a different way. At the early stages of their self-assembly, a reticular structure is formed, which then transforms into very long polysheaths composed of monomers. Along with polysheaths, rounded or lamplike structures 33–117 nm in size composed of the subunits of contracted sheaths are produced. Carotovoricins may serve as suitable objects for the study of the self-assembly of elementary biological structures.     

In Vitro Spermatogenesis in Lepidopteran Larvae: Role of the Testis Sheath

Summary

Premeiotic spermatocysts from testes of Heliothis virescens larvae were cultured in vitro. These eupyrene cysts progressed through meiosis and elongation in a medium containing calf serum in the absence of ecdysteroids. However, they also required the presence of the testis sheaths. The spermatogenesis-promoting effect of testis sheaths was dose dependent and varied with the donor's age. The active material was extractable from the tissue and was heat stable.