Periacineta mexicana n. sp. (Ciliophora,Suctoria, Discophryida), Epizoic on Mexican Backswimmers of the Genus Buenoa (Insecta,Hemiptera, Notonectidae)

ABSTRACT. A new species of suctorian in the genus Periacineta, epibiotic on aquatic bugs (Hemiptera, Heteroptera, Nepomorpha), is described on the basis of morphological characteristics of the cell body, lorica, tentacular placement, and stalk, and its 18S rRNA partial sequence gene. Periacineta mexicana n. sp. is a loricate suctorian with elongate body and rounded apical region; tentacles are distributed randomly over apical region and not grouped into fascicles. Macronucleus in adult is elongate and located centrally. The suctorian usually forms closely aggregated pseudocolonies. We provide morphological data based on optical and scanning electron microscopy. A comparison with similar congeners, and emended diagnosis of the genus Periacineta also are provided. The ciliates were found attached to the first two pairs of legs of Mexican notonectids Buenoa pallens and Buenoa spp. (backswimmers).     

A probable rhabdovirus infecting ryegrass (Lolium spp.)

A particle with morphology characteristic of the rhabdovirus group was found in leaf-dips and thin sections of symptomless Lolium spp. from several places in Britain. The particle was not transmitted mechanically nor by a number of groups of possible arthropod vectors. Despite the lack of conclusive evidence for the viral nature of the particle its morphology and intracellular localization strongly suggest that it is a member of the rhabdovirus group. This is the first report of such a particle in Lolium spp. and in Gramineae in Britain. The presumed virus is tentatively called ryegrass bacilliform virus (RBV).     

Ultrastructure and movements of cell structures in normal pea and an ageotropic mutant

The pea mutant (Pisum sativum ageotropum) and the normal pea (P. sativum cv. Sabel) were compared in order to see if there were any differences in root anatomy or submorphology which could explain the presumed ageotropic behaviour of the mutant. In both types the root cap consists of a central core (columella) distinct from the peripheral part. The core contains five to six rows of columella cells, each consisting of 10 to 16 storeys of statocytes. The ultrastructure of the columella cells in the two types is very similar; the main difference is confined to the distribution of rough endoplasmic reticulum (ER), which in the mutant statocytes is evenly distributed throughout the cell, while in the normal pea statocytes it is mainly concentrated in the distal part at the “floor” of the cell. Using light micrographs, the movement of amyloplasts and nuclei have been followed in detail during a 40 min inversion period. The pattern of movement of the amyloplasts is apparently identical in the two types and the distances moved during the inversion period are 39 μm and 44 μm in the normal and mutant statocytes, respectively. The nucleus has not been observed to move in normal pea; a slight rearrangement of the nucleus position can be observed during the period 30 to 40 min after the start of inversion of the mutant. Based on magnified electron micrographs of the statocytes a morphometrical analysis was made of five cell structures – amyloplasts, nuclei, mitochondria, vacuoles and ER – which appeared to be freely movable or redistributable under the influence of the gravitational force.     

Microsilica as antigen carrier and adjuvant in the Atlantic salmon (Salmo salarL.)

Bovine serum albumin and a glycine/HCl extract fromAeromonas salmonicidawere most effectively adsorbed to microsilica particles at pH 5·0 compared with pHs of 6·0, 7·0, 8·0 and 9·0. Atlantic salmon were immunised by intraperitoneal injection of the glycine/HCl extract fromA. salmonicidaadsorbed to microsilica. Antibody titres againstA. salmonicidaantigens demonstrated a prominent adjuvant effect of the microsilica 8 weeks after immunisation compared with soluble antigens. The duration of the antibody response suggests that microsilica may have some depot effect. The antibody response was, however, lower than the response obtained with Freund's complete adjuvant. Microsilica stimulated the respiratory burst activity in cultured Atlantic salmon head kidney macrophages. Some side effects of the microsilica were observed. Adhesions between abdominal organs and between the organs and the peritoneum were distinct. In addition, a dark greyish pigmentation at the sites of adhesion was evident. Cultured macrophages in the presence of high concentrations of microsilica resulted in toxic effects on the cells.     

Changes in Leaf Gas Exchange Properties of Cloned Betula pendula Saplings after Partial Defoliation

The effects of partial defoliation on the gas exchange characteristicsof the remaining leaves were studied in cloned Betula pendulaL. saplings grown in pots on two different soil types: prefertilizedpeat and unfertilized sand (Experiment 1). The responses ofundamaged leaves to different damage modes of leaf laminae werealso studied using saplings grown on prefertilized peat only(Experiment 2). In Experiment 1, removal of the upper leaves,which represented about half the total leaf area, approximatelydoubled the mean net photosynthetic rates of the remaining lowerleaves on both soil types and at both measuring dates (12–13d and 34 d after assigning the treatments). However, when thelower leaves were removed there was a temporary increase inthe mean net photosynthetic rates of the remaining expandedupper leaves only in the plants grown on sand. In Experiment2, the removal of laminae caused a similar increase in the light-saturatednet photosynthetic rates of the remaining leaves, irrespectiveof whether the laminae were removed totally immediately or graduallyin three stages. The magnitude of the photosynthetic responsewas determined by the amount of leaf tissue removed and wasindependent of the way in which it was removed. We concludethat the increase in the photosynthetic rates of the remainingleaves after partial defoliation may be attributed to the alleviatedcompetitive status among the leaves rather than to the decreasedsource/sink ratio within a plant. Key words: Partial defoliation, net photosynthesis, Betula pendula, birch sapling, herbivory     

Clinical,Pathological, and Etiologic Aspects of Acquired Dermal Melanocytosis

To study the pathogenesis of acquired dermal melanocytosis (ADM), we reviewed the clinical, immunohistochemical, and ultrastructual features of 34 cases (female, 33, and male, 1) of ADM. The patients’ ages at onset ranged from 8 to 51 years and averaged 26.8+12.7 years. There was a positive family history. Gray-brown macules were mostly recognized on the face. Not only active dermal melanocytes but also non-pigmented c-KIT-and TRP-2-positive immature melanocytes were detected in the dermis. Taken together those clinical and histological findings, activation of pre-existing immature melanocytes by sunlight, estrogen, and/or progesterone, and some other factors, may be the most likely mode of the development of ADM. Moreover, using cultured murine neural crest cells as a model of c-KIT-positive immature melanocytes, we confirmed that endothelin-1, which is produced and secreted by keratinocytes after UV-irradiation, affects melanocytes and accelerated melanogenesis.     

Responses of Daphnia pulex populations to toxic cyanobacteria

1. We studied the effects of toxic cyanobacteria, Microcystis aeruginosa , on Daphnia pulex populations. The experiment was performed at room temperature in laboratory microcosms to which we added toxic Microcystis in two pulses. Green alga, Scenedesmus obtusiusculus, was provided in two concentrations.
2. Microcystis exposure resulted in a decreased population density of Daphnia. The proportion of adolescents was higher in the Microcystis treatment than in the control, while the proportion of newborns did not differ significantly from the control. This indicates delayed maturation of Daphnia exposed to Microcystis . We found no significant impacts of cyanobacteria, food level or clonal origin on population variability after correcting for differences in population size.
3. Juveniles of the two clones studied showed different sensitivities to toxic Microcystis in the acute test. However, in the population experiment we did not find clonal differences between Microcystis and control treatments in the relative proportion of juveniles.
4. The number of ephippia produced per adult was highest in the treatments with Microcystis. This indicates that cyanobacterial toxins may be one of several factors inducing ephippia formation, acting directly or through inhibition of feeding.     

Sensitivity of Daphnia to toxic cyanobacteria: effects of genotype and temperature

1. We studied the effects of both acute and chronic exposure of Daphnia pulex to toxic Microcystis aeruginosa . We focused on the effects of Daphnia genotype and temperature (19 and 24 °C).
2. The study revealed variation among ten Daphnia pulex clones in survivorship under acute Microcystis exposure, measured as EC₅₀. An increase in temperature caused a clear decrease in EC₅₀, although the ranking of clones according to sensitivity remained the same at both temperatures.
3. In the chronic exposure of two of the clones, toxic Microcystis reduced survival and reproduction. The two clones differed in their responses, indicating different means of coping with toxic cyanobacteria. Toxic cyanobacteria reduced slightly more at 24 °C than 19 °C.
4. The clonal difference in sensitivity to toxic cyanobacteria at acute exposure was reversed at chronic exposure. This indicates that the results from short-term toxicity cannot be used to predict life history responses under sublethal exposure.