Synthesis and Secretion of Transferrin by Cultured Mouse Hepatoma Cells

The mouse hepatoma cell (Hepa-1) in tissue culture has been shown to synthesize and secrete three electrophoretically distinct transferrins. Each of these forms of transferrin has a molecular weight of 77,000, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The concentration of each form is indicated by its staining intensity, which is highest in the form with the fastest mobility and lowest in the form with the slowest mobility. The relative rate of transferrin synthesis has been determined in log-phase and stationary-phase cells; the data indicate that the relative rate of synthesis increases twofold in stationary-phase cells. When the incorporation of [³H]leucine into transferrin reaches steady state, the rate of secretion is equal to the rate of synthesis; the rate of secretion also increases twofold in stationary-phase cells. Our studies also show that transferrin synthesis accounts for 0.98% of the total protein synthesis in log-phase cells and for 1.8% in stationary-phase cells. This is the level of synthesis that has been determined by in vivo studies. We conclude that after continuous culture for several years these hepatoma cells have maintained one of the characteristics of the differentiated liver cell, namely, the ability to synthesize and secrete transferrin.     

Insect-oriented locomotor responses by unmated females of Ephestia cautella (Walker) (Lepidoptera: Phycitidae)

Unmated E. cautella of both sexes were caged together and the ensuing behaviours of females were recorded, with particular attention to orientations to other insects. Calling females engaged in ‘turning-to-face’ and ‘walking up to’ orientations directed almost exclusively at wing-beating males (flying, or sexually excited and ambulatory). Non-calling, locomoting females engaged in ‘flying at’, ‘landing near’ and ‘walking into’ orientations directed predominantly at wing-beating or resting males, and occasionally at mating pairs or at calling females. The activities of the orienting female led to changes in the behaviour of some target insects, and 4% of all females mated directly after approaching males. Results are discussed in relation to sexual receptivity, locomotory excitation, and the pheromonal control of this species.     

Responses of High Arctic wet sedge tundra to climate warming since 1980

The global climate is changing rapidly and Arctic regions are showing responses to recent warming. Responses of tundra ecosystems to climate change have been examined primarily through short‐term experimental manipulations, with few studies of long‐term ambient change. We investigated changes in above‐ and belowground biomass of wet sedge tundra to the warming climate of the Canadian High Arctic over the past 25 years. Aboveground standing crop was harvested from five sedge meadow sites and belowground biomass was sampled from one of the sites in the early 1980s and in 2005 using the same methods. Aboveground biomass was on average 158% greater in 2005 than in the early 1980s. The belowground biomass was also much greater in 2005: root biomass increased by 67% and rhizome biomass by 139% since the early 1980s. Dominant species from each functional group (graminoids, shrubs and forbs) showed significant increases in aboveground biomass. Responsive species included the dominant sedge species Carex aquatilis stans, C. membranacea, and Eriophorum angustifolium, as well as the dwarf shrub Salix arctica and the forb Polygonum viviparum. However, diversity measures were not different between the sample years. The greater biomass correlated strongly with increased annual and summer temperatures over the same time period, and was significantly greater than the annual variation in biomass measured in 1980–1983. Increased decomposition and mineralization rates, stimulated by warmer soils, were likely a major cause of the elevated productivity, as no differences in the mass of litter were found between sample periods. Our results are corroborated by published short‐term experimental studies, conducted in other wet sedge tundra communities which link warming and fertilization with elevated decomposition, mineralization and tundra productivity. We believe that this is the first study to show responses in High Arctic wet sedge tundra to recent climate change.     

Light,nutrients and the fatty acid composition of stream periphyton

1. While the balance of light and nutrients is known to influence the food quality of herbivores by altering algal phosphorus and nitrogen content, the combined effects of light and nutrients on fatty acid synthesis in freshwater periphyton are relatively unknown. In this study, we manipulated light and phosphorus concentration in large, flow‐through experimental streams to examine their effects on both elemental stoichiometry and fatty acid content in periphyton. 2. Two levels of phosphorus (4 and 80 μg L^?1) and three of light (17, 40, 110 μmol photons m^?2 s^?1) were applied in a factorial design in two separate experiments. Diatoms dominated periphyton communities in both experiments, comprising >95% of algal biovolume. Periphyton growth in the streams was simultaneously affected by both resources, even at low rates of supply. 3. Periphyton C/P and C/N ratios increased with light augmentation and decreased with phosphorus enrichment, and consistent with the light : nutrient hypothesis (LNH). Light effects were strongest in streams with low phosphorus concentrations. 4. Periphyton fatty acids reflected the dominance of diatoms : palmitic (16 : 0), palmitoleic (16 : 1ω7) and eicosapentanoic (20 : 5ω3) were the principal saturated (SAFA), monounsaturated (MUFA) and polyunsaturated fatty acids (PUFA), respectively. Linoleic (18 : 2ω6) and linolenic (18 : 3ω3) acids, characteristic of chlorophytes and cyanophytes, were rare, comprising <2% of total fatty acids. 5. Periphyton fatty acid profiles were highly sensitive to light and phosphorus. The proportion of fatty acids comprised by SAFA and MUFA increased with light augmentation and decreased with phosphorus enrichment, whereas PUFA decreased with light and increased with phosphorus. Light effects on fatty acid composition were strongest in phosphorus‐poor streams. PUFA declined with increasing light/phosphorus ratios in the streams, whereas ‘energy’ fatty acids (16 : 0 and 16 : 1) increased. The ratio of SAFA/PUFA was strongly and positively correlated with C/P and C/N ratios. SAFA and MUFA, normalised to dry mass, increased two‐ to threefold with increasing light, while PUFA normalised to dry mass was not significantly affected by light. 6. Similarities in the responses of fatty acids and elemental stoichiometry to light and phosphorus treatments suggested that they were influenced by a common mechanism. Both components of food quality appeared to be sensitive to light‐regulated rates of carbon fixation which, when coupled with insufficient supplies of phosphorus, caused diatom cells to store surplus carbon in SAFA, MUFA and other carbon‐rich compounds that diluted both essential fatty acids and mineral nutrients.