The consequences of infection of rainbow trout, Salmo gairdneri Richardson, by an acanthocephalan, Pomphorhynchus laevis Muller, have been studied using light and electron microscopy. The mucosal epithelium, of the gut adjacent to the metasoma of the worm suffered compression and abrasion. The praesoma of P. laevis penetrated the mucosal epithelium, lamina propria, stratum compactum, stratum granulosum, muscularis and serosa of the gut wall, and was invested by a fibrous capsule of inflammation tissue. This was composed of four principal cell types: eosinophilic granular cells (EGCs), type A cells, type B cells and fibroblasts. Some melanocytes and lymphocytes were also present. The role of the EGCs in the inflammation response is not known, but may not be an active one. The type A cells resembled neutrophils of other fish species, and have tentatively been placed in this category. The type B cells, with large cisternae formed by the RER, resembled plasma cells and may have been involved in a humoral response to the acanthocephalan. The integument of P. laevis did not appear to be damaged by the cells of the inflammation tissue, and it seems likely that this host response was incapable of rejecting the parasite.
The mechanism of cytokinin-induced cell expansion in cotyledons excised from dark-grown seedlings of radish (Raphanus sativus L.) and cucumber (Cucumus sativus L.) was studied. Cotyledons were incubated in dim light with or without 17 micromolar zeatin for periods up to 3 days. Fresh weights and osmotic potentials were measured daily. Cell wall extensibility properties were measured before and after the growth period. Also, experiments in which radish cotyledons were grown in mannitol solutions of various concentrations were performed. Comparisons of growth rates and increases of tissue osmotic potentials (toward zero) during growth without mannitol indicate that wall extensibility increased during the growth period and that this extensibility was enhanced by zeatin.Extensibility values derived from growth rates in mannitol provided indirect evidence of zeatin-increased wall extensibility. These conclusions were verified by direct measurements of plasticity with an Instron extensiometer. Thus, growth stimulation of excised cotyledons by cytokinins apparently involves wall loosening, in addition to previously demonstrated increases of K(+) absorption and formation of reducing sugars.
Changes indueed in intestinal and rectal structure of the stone loach, Noemacheiltis barbatulus (L.) by Pomphorhynchtis laevis Muller infeetion are described. Within the gut, the main effect of the infection is the abrasion and flattening of the mueosa by the parasite. Where the praesoma penetrates the gut wall, there is a marked inflammatory response. This inflammatory response tissue is well vascularized and displays esterase activity. Granulocytes and phagocytic cells, whieh are found both within the inflammation tissue and within capillaries, are probably host leucocytes. The integument of P. laevis appears undamaged by granulocytes in its proximity and it is unlikely that the host's inflammatory respotise is capable of rejecting the parasite.
Materials and methodsStone loach collected from the River Severn, Shropshire (NGR SJ/396153) were maintained in the laboratory in 30x30x60 cm tanks supplied with constantly flowing filtered water at 19°C. Fish for investigation were killed by a blow on the head, the gut removed and examined for parasites prior to placement in the appropriate fixative. A total of 19 fish were examined for parasite-induced changes.
Light MicroscopyPortions of gut were fixed in phosphate-buffered formalin, dehydrated in ethanolic series, cleared in xylol and embedded in Paraplast (BDH, Poole, Dorset, UK) before sections 6-jLtm
Light and electron microscopy revealed no stimulation of oleosome disappearance or chloroplast development associated with zeatin‐enhanced growth of excised radish cotyledons. Accelerated protein body breakdown was the only detectable effect of zeatin treatment. Isocitrate lyase activity, disappearance of total lipids, and appearance of galactolipids, phospholipids, and chlorophyll were unaffected by zeatin. Results indicate that cytokinins do not accelerate conversion of radish cotyledons from storage to photosynthetic organs.
The digenean Allocreadium transversale (Rud.) has been recorded once previously in Great Britain. During work on the feeding of Cobitis taenia (L.) it was found to be a frequently occurring gut parasite. Great variation occurred in its seasonal level of incidence and mean worm burden, indicating a rapid turnover and replacement of the parasite in the fish. No significant relationship could be shown between the level of infection and age of the fish; but a highly significant relationship occurred between incidence of infection and fish age.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.