Infection Behavior and Overwintering Survival of Foliar Nematodes, Aphelenchoides fragariae, on Hosta

We studied the pathogenicity and overwintering survival of the foliar nematode, Aphelenchoides fragariae, infecting Hosta spp. Nematodes applied to either lower or upper sides of noninjured and injured hosta leaves were able to infect and produce typical symptoms on nine cultivars. Leaves of only four cultivars (Borschi, Fragrant Blue, Patomic Pride, and Olive Bailey Langdon) showed no symptoms of nematode infection. The nematodes overwintered as juveniles and adults in soil, dry leaves, and dormant buds, but not in roots. Nematode winter survival was higher in dormant buds and soil from the polyhouse than in an open home garden. Of the nematodes found in the dormant buds, 35% to 79% were located between the first two outside layers of the buds. The nematodes tolerated 8 hr exposure to 40°C and −80°C in leaf tissues. Relative humidity influenced nematode migration from soil to leaves. The presence of nematodes only on the outer surface of foliage (leaves and petioles) confirmed the migration of A. fragariae on the surface of the plants. Of the total number of nematodes found on the foliage, 25% to 46% and 66% to 77% were alive at 90% and 100% relative humidity, respectively, suggesting that high moisture is required for the survival and upward movement of nematodes. We conclude that A. fragariae can overwinter in soil, infected dry leaves, and dormant buds and migrate in films of water on the outer surface of the plant during spring to leaves to initiate infection.     

A two-stage fed-batch heterotrophic culture of Chlorella protothecoides that combined nitrogen depletion with hyperosmotic stress strategy enhanced lipid yield and productivity

In this study, the influences of major nutrients on cell growth and lipid production were investigated in heterotrophic culture of Chlorella protothecoides. The results demonstrated that phosphorus depletion had no effect on lipid accumulation but restricted cell growth; however, nitrogen depletion could enhance lipid accumulation thus benefiting lipid production. Furthermore, the effects of glucose inhibition were comparatively investigated with osmotic stress, showing that the effects of glucose inhibition were similar to the effect of osmotic stress at equivalent osmotic pressures only if the glucose concentration was less than 100 g/L, otherwise the effects of glucose inhibition became much stronger than osmotic stress. Interestingly, it was found that a specific hyperosmotic stress could significantly enhance lipid accumulation, thus providing a new stress strategy for efficient lipid production. Finally, a novel two-stage fed-batch culture consisting of a growth phase and a lipid accumulation phase with nitrogen depletion and hyperosmotic stress was proposed, yielding a final lipid productivity of 177.3 mg/L/h with a very high lipid yield of 207.0 mg/g glucose and lipid content of 39.2% after 180 h culture, which were 1.60, 1.79 and 1.92-fold of those obtained in one-stage fed-batch culture without stress phase, respectively.     

The Influence of Environmental Factors on the Respiration of Plant-Parasitic Nematodes

Respiration of selected nematode species was measured relative to CO₂ level, temperature, osmotic pressure, humidity, glucose utilization and high ionic concentrations of sodium and potassium.In general, respiration was stimulated most by the dominant environmental factors at levels near those expected in the nematode''s "natural" habitat. Soil-inhabiting nematodes utilized O₂, most rapidly with high (1-2%) CO₂ whereas a foliar nematode (Aphelenchoides ritzemabosi) did so with 0.03% CO₂, the concentration typically found in air. Temperature optima for respiration corresponded closely to those for other activities. Ditylenchus dipsaci and Pratylenchus penetrans adults and Anguina tritici and A. agrostis second-stage larvae respired within the range of osmotic pressures from 0 to 44.8 arm and respiration of their drought-resistant stages was stimulated by increasing osmotic pressure which accompanies the onset of drought. Rehydration of A. tritici and A. agrostis larvae with RH as low as 5% stimulated measurable respiration. Glucose utilization from liquid medium by A. tritici larvae or A. ritzembosi was not detectable. Supplemental Na⁺ stimulated respiration of Anguina tritici, K⁺ did not.     

Heterodera glycines: eggshell ultrastructure and histochemical localization of chitinous components

The eggshell in most nematodes consists of an outer vitelline layer, a middle chitinous and an inner lipid layer. Earlier work with eggs of Heterodera glycines suggests the presence of two chitinous layers but the vitelline layer was not observed. From our observation the outer chitin layer described in past literature is actually a vitelline layer. Histochemical analysis has demonstrated that chitin is absent from the outer envelope. Electron microscope observations of the eggshell show a waxy appearance and osmium staining consistent with that of the proteinaceous vitelline layer found in other nematodes. Lectin localization also shows that the eggshell continues to develop past fertilization with the delivery and integration of eggshell precursors. Contrary to previous reports, we propose that the ultrastructure of the eggshell H. glycines follows the common three-layer structure observed in other nematodes.     

模拟喀斯特生境条件下干旱胁迫对青冈栎苗木的影响

为了研究喀斯特"双层"地质结构对植物的影响,以及在干旱环境下,喀斯特地区植物的生理变化与适应策略,建立"土壤层-岩石(石灰岩)层-岩溶水层"水分供应分层模拟柱,对‘土壤层’设置不同水分梯度,种植青冈栎(Cyclobalanopsis glauca)苗木进行干旱胁迫试验,测定青冈栎的叶面积、比叶面积、生物量、渗透调节物质含量、相对叶绿素含量。结果表明:在模拟柱‘岩溶水层’加水条件下,植物根系能下扎至‘岩溶水层’,‘土壤层’干旱胁迫对青冈栎的生理变化没有产生影响;在‘岩溶水层’无水条件下,青冈栎生理变化受‘土壤层’干旱胁迫影响显著,‘土壤层’水分含量越低,青冈栎的叶面积、生物量、叶绿素含量、叶片相对含水量越小,青冈栎干鲜比、根冠比、可溶性糖、丙二醛和脯氨酸含量越高。青冈栎幼苗利用岩溶水层水分是适应喀斯特干旱环境的重要策略。     

The effect of <Emphasis Type="Italic">Cercidium praecox</Emphasis> and <Emphasis Type="Italic">Prosopis laevigata</Emphasis> on vertical distribution of soil free-living nematode communities in the Tehuacán Desert,Mexico

Vegetation cover is known to act as an abiotic mediator influencing the structure of soil fauna communities in arid and semi-arid ecosystems. The aim of the current research was to determine the spatial dispersion of the soil free-living nematode community under the canopy of Cercidium praecox and Prosopis laevigata during the rainy season. These shrubs are the dominant plant associations in the western part of the Tehuacán-Cuicatlán Valley in Mexico. Soil samples were taken from each 10-cm depth between 0 and 50 cm in August 2004. Our results demonstrated that the abundance and structure of the soil free-living nematode communities in the study area were strongly dependent on plant effects, specified by limited factors such as soil moisture and organic matter availability. The greatest degree of abundance of soil-free-living nematodes (88%) was found in the upper (0–10 cm) soil layer. Plant parasites were the most abundant trophic group under the two plants (58 and 36% under Parkinsonia (Cercidium) praecox and Prosopis laevigata, respectively), whereas omnivore-predators were the most dominant (96%) in inter-plant spaces. The fungivore/bacterivore (F/B) ratio was found to be the most useful tool of the ecological indices tested in the present study, reflecting the vertical distribution of the free-living nematode communities beneath different plant species in the different soil layers. The soil free-living nematode communities and their vertical distribution were found to be affected by plant ecophysiological adaptation, soil moisture, and the interaction between them.     

Distribution of Tardigrades within a Moss Cushion: Do Tardigrades Migrate in Response to Changing Moisture Conditions?

The distribution of tardigrades within the layers of the cushion moss Grimmia alpicola Hedwig, 1801 was investigated. The aim of this study was to determine the tardigrade species present within the moss layers during both wet and dry periods and to determine if migration occurred in response to changing moisture conditions. Samples of the moss were removed from concrete caps on brick fence posts before and after rainfall and separated into two sections (top and bottom). The tardigrades from each layer and moisture condition were identified to species. Data for each species were statistically analyzed with a two-way analysis of variance (ANOVA) to compare the numbers of individuals present in the top and bottom layers of the moss under both wet and dry conditions.

Five tardigrade species were identified, including two species new to science: Macrobiotus sp. n.; Milnesium tardigradum Doyère, 1840; Echiniscus viridissimus Peterfi, 1956; Echiniscus perviridis Ramazzotti, 1959; and Echiniscus sp. n. The new species will be described in a forthcoming paper. No significant differences were found in the numbers of individuals of four of the five species in each layer within the moss or for each moisture condition. Only one species, E. viridissimus, was significantly more frequent in the top layer of the moss, regardless of moisture condition.

Migration within the moss cushion was not detected in any of these five species as a result of changes in moisture conditions. In xeric moss species, it may not be beneficial for tardigrades to migrate to avoid desiccation. Instead, they apparently undergo anhydrobiosis in both the top and bottom layers of the moss cushion.     

Ultrastructural studies on the nematode Xiphinema diversicaudatum: Egg shell formation

The ultrastructure of the formation of the egg shell in the longidorid nematode Xiphinema diversicaudatum is described. Upon fertilization a vitelline membrane, which constitutes the vitelline layer of the egg shell, is formed. The chitinous layer is secreted in the perivitelline space, between the vitelline layer and the egg cell membrane. On completion of the chitinous layer, the material of the lipid layer is extruded from the egg cytoplasm to the outer surface, through finger-like projections. Both chitinous and lipid layers are secreted by granules in the egg cytoplasm that disappear as the layers are completed. Chitinous and lipid layers are formed during the passage of the egg through the oviduct. The vitelline layer is enriched with secretions produced by the oviduct cells and then by phospholipids secreted by the cells of the pars dilatata oviductus. The inner uterine layer is also formed by deposition of secretory products apposed on the egg shell in the distal uterine region and Z-differentiation. In the proximal part of the uterus, the egg has a discontinuous electron-dense layer, the external uterine layer. Tangential sections between chitinous and uterine layers revealed the presence of holes, possibly egg pores, delimited by the two uterine layers.     

Distribution of lipopolysaccharide and the detection of a new subfraction in the cell envelope of a marine pseudomonad.

The three outer layers of the cell envelope of marine pseudomonad B-16, the loosely bound outer layer, the outer membrane, and the periplasmic space layer, are the only ones containing appreciable amounts of both lipid and carbohydrate. These layers and a fraction released into the medium during growth of the cells were examined for the presence of common antigens by double immunodiffusion using anti-whole serum. Each of the layers, the medium fraction, and lipopolysaccharide (LPS) isolated from the organism were shown to contain two or more diffusible components showing reactions of identity. Thus LPS is found in each of the three outer layers of the cell envelope of this gram-negative bacterium. The periplasmic space layer was found to contain a fraction accounting for 20% of the dry weight of the layer, which was sedimentable at 30,000 x g and contained lipid, protein, and carbohydrate. Double-immunodiffusion tests indicated that the fraction contained at least one of the two antigens present in isolated LPS. A particulate material was released by the cells during growth which gave a positive test for 2-keto-3-deoxyoctulosonic acid and cross-reacted serologically with LPS.     

Anhydrobiotic Coiling of Nematodes in Soil

Nematodes of three genera (Acrobeloides sp., Aphelenchus avenae, and Scutellonema brachyurum) were induced to coil and enter anhydrobiosis in drying soil of two types: sandy loam and loamy sand. Coiling was studied in relationship to soil moisture characteristics. Coiling and the physiological state of anhydrobiosis occurred before the water in sandy soils reached a water potential of -15 bars. Coiling was maximum at 3-6 bars, depending on the soil type and nematode species. It appeared that induction of coiling and anhydrohiosis were determined by the physical forces exerted by the water film surrounding the nematode, which, for these three species, was 6-9 monomolecular layers of water, rather than the % moisture and relative humidity of the soil per se.     

The structure of the egg-shell of Porrocaecum ensicaudatum (Nematoda: Ascaridida)

Wharton D. A. 1979. The structure of the egg-shell of Porrocaecum enslcaudatum (Nematoda: Ascaridida). International Journal for Parasltology9: 127–131. The egg-shell of Porrocaecum ensicaudatum is oval with an opercular plug at either end. The shell consists of three layers: an inner lipid layer, a middle chitinous layer and an outer vitelline layer. The vitelline layer has strands of particulate material attached to its outer surface. The chitinous layer consists of 8.5 nrn fibrils which are made up of a chitin microfibril core surrounded by a protein coat. The fibrils are oriented randomly or in parallel, there being no indication of helicoidal architecture.The chitinous layer varies in thickness to form a pattern of interconnecting ridges on the surface of the egg. This pattern presumably increases the shell's structural strength.     

Ultrastructural Variation of Cuticular Layers in Cephalobinae (Nemata: Rhabditida)

The ultrastructure of the body wall cuticle in Acrobeles complexus, Cervidellus alutus, and Zeldia punctata was studied as a step toward understanding biological diversity within Cephalobinae, and to discover new characters for phylogeny-based classification of the suborder. In each species the cuticle consists of cortical, median, and basal layers. The cortical layer includes an external trilaminate and internal granular zone; the basal layer is striated. In Z. punctata the median layer is electron-lucent, vacuolar, and penetrates the cortical layer; it also includes periodically dense columns that apparently correspond to punctuations visible with light microscopy. In contrast, the median layer of the body wall cuticle in A. complexus and C. alutus is bisected by a zone that undulates parallel to the nematode surface and with periodicity corresponding to annuli. Phylogenetic analysis, using derived cuticle patterns of Cephalobinae, requires an understanding of ecological pressures that could result in convergent evolution of cuticle characters.     

Isolation, Composition, and Structure of Membrane of Listeria monocytogenes

The plasma membrane of Listeria monocytogenes strain 42 was prepared by osmotic lysis of protoplasts with tris(hydroxymethyl)aminomethane (Tris) buffer, pH 8.2, containing MgCl₂ and glucose, followed by washing with NaCl and MgCl₂ in Tris buffer. Electron microscopy showed that the preparation was not contaminated with cytoplasmic material. The membrane preparation was composed of 55 to 60% protein, 1.5% ribonucleic acid, 0.1% deoxyribonucleic acid, 1.3 to 2.3% carbohydrate, 0.17 to 0.38% amino sugar, 0.2 to 0.4% rhamnose, 3.5 to 4.0% phosphorus, 10.5 to 12.0% nitrogen, and 30 to 35% lipid. Amino acid composition of the washed membrane showed some variation from that of the whole cells. Sulfur-containing amino acids were not present in the membrane hydrolysate. The membrane carbohydrate contained glucose, galactose, ribose, and arabinose. The membrane lipid was 80 to 85% phospholipid and 15 to 20% neutral lipid. The lipid contained 2.3 to 3.0% phosphorus, 2.5 to 3.0% carbohydrate, and a very small amount of nitrogen (0.2 to 0.3%). The phospholipid was of the phosphatidyl glycerol type. Electron micrographs of the washed membrane showed three layers. The outer and inner layers varied in thickness from 25 to 37 A and the middle layer from 20 to 25 A. The total thickness varied between 85 and 100 A. These preparations contained many vesicles which stained heavily with lead citrate. Some vesicles were also attached to the protoplast ghosts in the form of extrusions or intrusions, or both. Membrane preparations obtained by lysis of protoplasts in the absence of MgCl₂ were fragmented and contained less lipid (20 to 22%) and ribonucleic acid (0.3 to 0.5%) than preparations prepared with MgCl₂.     

Cutaneous water loss and lipids of the stratum corneum in two syntopic species of bats

The lipid matrix of the stratum corneum (SC), the outer layer of the epidermis of mammals and birds, constitutes the barrier to diffusion of water vapor through the skin. The lipids of the SC are structured in the intercellular spaces of the mammalian epidermis in ordered layers, called lamellae, which have been postulated to prevent water loss. Lipids in the mammalian SC are mainly cholesterol, free fatty acids and ceramides, the latter forming the structural support for the lamellae. However, knowledge on how the lipid composition of the SC alters cutaneous water loss (CWL) in mammals is rudimentary, and is largely derived from studies on laboratory animals and humans. We measured CWL of individuals of two species of syntopic bats, Tadarida brasiliensis and Myotis velifer. In the first study of its kind on wild mammals, we correlated CWL with the lipid composition of the SC, measured using thin layer chromatography and high performance liquid chromatography coupled with atmospheric pressure photoionization mass spectrometry. Surface-specific CWL was 20.6% higher in M. velifer than in T. brasiliensis, although differences were not significant. Compared with individuals of M. velifer, individuals of T. brasiliensis had more classes, and a higher proportion, of polar ceramides in the SC, a feature associated with lower CWL. Individuals of T. brasiliensis also had a class of non-polar ceramides that presumably spans the lamellae and gives more cohesiveness to the lipid matrix of the SC. We conclude that qualitative and quantitative modifications of the lipid composition of the SC contribute to regulate CWL of these two species of bats.     

Origin and evolution of the unusual leaf epidermis of Caryodaphnopsis (Lauraceae)

We studied leaf epidermal anatomy of Caryodaphnopsis Airy Shaw, a genus disjunct between tropical Asia and tropical America, using light microscope and scanning electron microscope. We sampled 10 species of Caryodaphnopsis and 52 species of other Lauraceous genera. Our observations suggest that this genus possesses a unique lower leaf epidermis. Compared with other leaves of Lauraceae, this genus has an additional layer covering the lower leaf epidermis and the stomatal apparatus. The additional layer is either closed or poriferous/reticulate. The outer periclinal walls of the lower leaf epidermis protrude outside forming hollow domes or columns, and the distal endings of these domes or columns are expanded and fused, which forms the additional covering layer. Three different types are recognized in the genus: (1) the middle portion of the protuberances is not contracted and the distal endings are free or adnate to each other, with only limited space between the two layers; (2) the middle portion is slightly contracted in the outer part, the distal endings are fused, with more space between the two layers; (3) the middle portion is conspicuously contracted and elongated into columns, the distal endings are fused and it is roomy between the two layers. The structure of the leaf lower epidermis is reconstructed and illustrated for the first time. This unusual leaf lower epidermis of Caryodaphnopsis is derived in Lauraceae and is an autapomorphic character. Outward protrusions of the outer periclinal walls forming papillate protuberances surrounding the stomatal apparatus are also found in a few other genera including Neocinnamomum, a genus closely related to Caryodaphnopsis, but the distal endings of these protrusions are not expanded and connected. We hypothesize that the periclinal wall of the lower leaf epidermis has been gradually modified in Lauraceae, from a smooth pattern in most genera, to papillate pattern (e.g. Neocinnamomum), and to the double layered lower leaf epidermis in Caryodaphnopsis. The origin and evolution of this unique lower epidermis might have been related to the climatic cooling and aridification since the late Eocene.     

Anther ontogeny in <Emphasis Type="Italic">Brachypodium distachyon</Emphasis>

Brachypodium distachyon has emerged as a model plant for the improvement of grain crops such as wheat, barley and oats and for understanding basic biological processes to facilitate the development of grasses as superior energy crops. Brachypodium is also the first species of the grass subfamily Pooideae with a sequenced genome. For obtaining a better understanding of the mechanisms controlling male gametophyte development in B. distachyon, here we report the cellular changes during the stages of anther development, with special reference to the development of the anther wall. Brachypodium anthers are tetrasporangiate and follow the typical monocotyledonous-type anther wall formation pattern. Anther differentiation starts with the appearance of archesporial cells, which divide to generate primary parietal and primary sporogenous cells. The primary parietal cells form two secondary parietal layers. Later, the outer secondary parietal layer directly develops into the endothecium and the inner secondary parietal layer forms an outer middle layer and inner tapetum by periclinal division. The anther wall comprises an epidermis, endothecium, middle layer and the secretory-type tapetum. Major documented events of anther development include the degradation of a secretory-type tapetum and middle layer during the course of development and the rapid formation of U-shaped endothecial thickenings in the mature pollen grain stage. The tapetum undergoes degeneration at the tetrad stage and disintegrates completely at the bicellular stage of pollen development. The distribution of insoluble polysaccharides in the anther layers and connective tissue through progressive developmental stages suggests their role in the development of male gametophytes. Until sporogenous cell stage, the amount of insoluble polysaccharides in the anther wall was negligible. However, abundant levels of insoluble polysaccharides were observed during microspore mother cell and tetrad stages and gradually declined during the free microspore and vacuolated microspore stages to undetectable level at the mature stage. Thus, the cellular features in the development of anthers in B. distachyon share similarities with anther and pollen development of other members of Poaceae.     

Effect of Temperature on Infection and Survival of Rotylenchulus reniformis

From infestation of lettuce with preinfective females to egg deposition, populations of Rotylenchulus reniformis from Baton Rouge, Louisiana; Lubbock and Weslaco, Texas; and Mayaguez, Puerto Rico, required 41, 13, 7, and 7 days at 15, 20, 25, and 34 C, respectively. No nematode infection occurred at 10 C with any R. reniformis population, and the population from Puerto Rico did not reproduce at 15 C. Nematode survival was not influenced by temperature, since populations from Texas and Louisiana survived for 6 months without a host at - 5 , - 1 , 4, and 25 C. Survival of R. reniformis was substantially influenced by soil moisture. Soil moistures greater than 7% (< 1 bar) aided nematode survival at storage temperature of 25 C, whereas moisture adversely affected nematode survival below freezing. Soil moisture below 4% (> 15 bars) favored nematode survival below freezing but adversely affected nematodes in soils stored at 25 C. Soil moisture effects on nematode survival were less accentuated at 4 and 0 C.     

Anther ontogeny in Campsis radicans (L.) Seem. (Bignoniaceae)

In this study anther ontogeny of Campsis radicans (L.) Seem. was investigated by transmission electron microscopy and light microscopy with special reference to the development of the anther wall. The anther wall formation follows the dicotyledonous type. The differentiation in anther starts with the appearance of archesporial cells which undergo periclinal divisions to give primary parietal layer to the epidermal site and the primary sporogenous cells to the inside. The primary parietal layer also divides to form two secondary parietal layers. Later, the outer secondary parietal layer (spl1) forms the endothecium and the middle layer by periclinal division whereas the inner one (spl2) directly develops into the outer tapetum forming the inner most layer of the anther wall. The sporogenous tissue is generally organized in two rows of cells with a horseshoe-shaped outline. The remainder of the tapetum lining the sporogenous mass is derived from the connective tissue. The tapetum thus has dual origin and dimorphic. Anthers are tetrasporangiate. The wall of the anther consists of an epidermis, endothecium, middle layer, and the secretory type tapetum. Tapetal cells are usually binucleated. Epidermis and Endothecium layers of anther wall remain intact until the end of anther and pollen development; however, middle layer and tapetum disappear during development.     

Stratification, composition, and function of marine mammal blubber: the ecology of fatty acids in marine mammals

Abstract This study of vertical fatty acid profiles, based on analysis of 58 fatty acids sampled at 3-mm intervals throughout the blubber column of a model marine mammal, the ringed seal (Pusa hispida), revealed three chemically distinct layers. The average depths of the outer and inner layers were quite consistent (approximately 1.5 and approximately 1 cm, respectively). Consequently, the middle layer varied greatly in thickness, from being virtually absent in the thinnest animals to 2.5 cm thick in the fattest. The relative consistencies of the thickness and composition of the layers as well as the nature of the fatty acids making up each layer support the generally assumed function of the various layers: (1) the outer layer is primarily structural and thermoregulatory, (2) the inner layer is metabolically active with a fatty acid composition that is strongly affected by recent/ongoing lipid mobilization/deposition, and (3) the middle layer is a storage site that contracts and expands with food availability/consumption. The remarkable dynamics of the middle layer along with the discrete pattern of stratification found in the vertical fatty acid profiles have important implications for methodological sampling design for studies of foraging ecology and toxicology based on analyses of blubber of marine mammals.