Catabolism of Tryptophan by Trypanosoma evansi

ABSTRACT. Trypanosoma brucei gambiense , which causes human African trypanosomiasis, catabolizes the aromatic amino acid tryptophan via an initial aminotransferase catalyzed reaction to form several indole end products, which have been suggested to contribute to the pathogenesis of trypanosomiasis. To determine if this same pathway exists in T. evansi , the closely related trypanosome pathogen of domestic animals, tryptophan catabolism was examined in vitro and in vivo. As is the case with human African trypanosomes, T. evansi catabolized tryptophan to form indole-3-pyruvic acid and smaller amounts of indole-3-acetic acid and indole-3-lactic acid. Large concentrations of indole-3-pyruvic acid are excreted in urine of trypanosome-infected mice. However, indole-3-ethanol could not be detected in incubates of T. evansi or T. b. gambiense , even though the latter species had previously been reported to form this neutral metabolite. A new, previously unreported tryptophan metabolite was isolated and partially characterized from incubates of T. evansi and T. b. gambiense. Although the functional significance of tryptophan catabolism to trypanosomatids remains obscure, the pathway is quantitatively significant in all species examined thus far.     

Selection of a suitable cladoceran species for toxicity testing in turbid waters

Abstract Two Australian cladocerans, Moina australiensis Sars and a species of Ceriodaphnia, were evaluated as possible biological indicator organisms to assess the toxicity of irrigation supply and drainage water of the Murrumbidgee and Coleambally Irrigation Areas. M. australiensis, being large (～2000 μm) and orange, was initially chosen to overcome visibility problems in highly turbid Australian inland waters. However, the organism responded erratically in culture. Mortality was high and neonate production was unpredictable when cultured under recommended United States Environmental Protection Agency protocols. Attempts to improve culture performance by optimizing food (quality and quantity), water (control source, hardness, volume) and temperature were only marginally successful. Similar difficulties were not evident when Ceriodaphnia sp. was used as the test organism. Although Ceriodaphnia sp. is small (～1000 μm), grey and more difficult to see in turbid water its responses were more predictable and reliable than those of M. australiensis. Results of initial trials comparing the two organisms suggest that Ceriodaphnia sp. was a better test organism and more suited to local requirements.     

Long- and short-term effects of decreased sink demand on carbohydrate levels and photosynthesis in wheat leaves

Wheat (Triticum aestivum L.) ears were removed to investigate long-term regulation of photosynthesis by sink demand at ambient CO₂ and 22 °C. The CO₂ level was also increased to 660 μmol mol^?1 and temperature was lowered to 5 °C to examine short-term responses of photosynthesis to low sink demand. Sink removal inhibited photosynthesis and increased leaf levels of glucose, fructose and ribulose-1, 5-bisphosphate (RuBP), and the glucose-6-phosphate (G6P)/fructose-6-phosphate (F6P) and RuBP/3-phosphoglycerate (PGA) ratios under growth conditions, but had no effect on the activity and activation state of ribulose-1, 5-bisphosphate carboxylase oxygenase (Rubisco) either under growth or short-term conditions, suggesting an inhibition of photosynthesis by decreased in vivo catalysis of Rubisco. Photosynthesis increased similarly in eared and earless shoots after a rise in CO₂ concentration, and the ratio of triose-phosphates (glyceraldehyde 3-phosphate and dihydroxyacetone phosphate, TP) to PGA was similar or higher for removed than intact ears, suggesting that feedback inhibition of photosynthesis was not caused by a limitation of ATP synthesis in chloroplasts. Under short-term conditions (660 μmol mol^?1 CO₂, 5 °C), TP and RuBP levels and the TP/PGA and TP/RuBP ratios were increased by sink removal, indicating an additional limitation of photosynthesis by the rate of RuBP regeneration.     

Seasonal Variation in Respiratory and Photosynthetic Parameters in Three Mosses from the Maritime Antarctic

Carbon fixation under controlled conditions was measured inthree mosses from the maritime Antarctic using an infra-redgas analysis system. Gas exchange parameters were determinedduring each season in 1993 and 1994 using the Arrhenius equationand a hyperbolic tangent function applied to respiration andphotosynthesis, respectively. Environmental data was collectedin 1994 for comparison. All seasonal variations were greaterinBrachythecium than in the species from less hydric habitats.Respiration rates were highest in summer and lowest in winterat all temperatures inBrachythecium, but there was little changeinChorisodontium orAndreaea . There was some seasonal variationin the initial slope (K_p) of the photosynthesis-irradiance curvein all species, although the environmental data suggested thatthis was of little ecological importance. In all species seasonalchanges in the maximum rates of photosynthesis (GP_max, NP_max)were observed, generally with a pattern of summer maxima, althoughthere were some interannual differences. These changes are consideredto be the most important in affecting the overall annual productivityof the mosses. There were no seasonal variations in the optimumtemperatures for either gross or net photosynthesis, or forthe irradiance at the onset of light saturation (I_k). The resultshave important implications for the use of models to estimatethe productivity of the Antarctic flora based upon present orpredicted climate data. Antarctica; bryophytes; mosses; carbon exchange; irradiance; photosynthesis; productivity models; respiration; seasonal variation; temperature     

Immunogenic potential of human bone marrow mesenchymal stromal cells is enhanced by hyperthermia

Background aims

Bone marrow–derived mesenchymal stromal cells (MSCs) have been reported to suppress T-cell proliferation and used to alleviate the symptoms of graft-versus-host disease (GVHD). MSCs are a mixed cell population and at this time there are no tools to isolate the cells responsible for the T-cell suppression. We wanted to find a way to enhance the immune-modulatory actions of MSCs and tried varying the temperature at which they were cultured.

Age‐related reproductive success in dichromatic male Black Redstarts Phoenicurus ochruros: Why are yearlings handicapped?

Reproductive constraints on sexually mature, young birds may be the underlying cause for the evolution and maintenance of delayed plumage maturation in passerine birds. I examined whether yearling male Black Redstarts in non-definitive plumage are reproductively handicapped and explored possible reasons for it. Yearlings raised only half as many young per season as adults. Differential reproductive effort was excluded as a possible source for age-related reproductive success because yearlings and adults did not differ in the frequency of non-breeding or in paternal effort. The lower annual reproductive success of yearlings was attributed to their lower probability of obtaining (multiple) females and adult females. Males mated to adult females raised almost twice as many offspring as males mated to yearling females. I conclude that the proposed preconditions for the evolution and maintenance of delayed plumage maturation do still prevail in the Black Redstart.