Impact of whitefish on an enclosure ecosystem in a shallow eutrophic lake: changes in nutrient concentrations,phytoplankton and zoobenthos

Large bag-type (75 m³) and tube-type (105 m³) enclosures were set up in the shallow eutrophic Lake Suwa and were each stocked with exotic planktivorous whitefish (Coregonus lavaretus maraena). The release of whitefish caused the increase in nutrient concentration in the tube-type enclosure whereas no such increase was observed in the bag-type enclosure. Bottom sediment seemed to be an important source of chironomid food for whitefish. The proportion of phytoplankton measuring<10μm and 20–40μm, which respectively corresponded toOchromonas spp. andCryptomonas sp., were lower in the fish enclosures than in the control, which might have been caused by high grazing pressure by rotifers. The predation by whitefish might have affected the species composition of phytoplankton through reducing copepod predation on rotifers, not through reducing the densities of cladocerans which directly feed on phytoplankton as many investigators have reported. The phytoplankton biomass was not affected much by the release of fish. Possible reasons are that the increase in density of rotifers reduced the biomass of available phytoplankton and also that inedible Cyanophyceae were in the decreasing phase of their seasonal succession and could not increase successfully in spite of elevated nutrient levels.     

Impact of whitefish on an enclosure ecosystem in a shallow eutrophic lake: selective feeding of fish and predation effects on the zooplankton communities

Bag-type enclosures (75 m³) with bottom sheets and tube-type enclosures (105 m³) open to the bottom sediment were stocked with exotic whitefish (Coregonus lavaretus maraena) to study their predation effects on the plankton community. The fish fed mainly on adult chironomids during the period of their emergence (earlier part of the experimental period). Thereafter, the food preference was shifted to larvae of chironomids and crustacean zooplankters. The predation effects on the plankton community were not evident in the bag-type enclosures where zooplankton densities were consistently low. The fish reduced the crustacean populations composed ofBosmina fatalis, B. longirostris andCyclops vicinus in the tube-type enclosures where the prey density was high (above ca. 50 individuals 1⁻¹). The results suggested that the intensity of predation depended on the prey density. Rotifers increased in the fish enclosure, probably becauseCoregonus reduced the predation pressure byCyclops vicinus on rotifers and allowed the latter to increase. In the fish enclosures, no marked changes in species composition were observed. Zooplankton predated by the fish seemed to be distributed near the walls of the enclosures. Problems of enclosure experiments for examining the effects of fish predation on pelagic zooplankton communities are discussed.     

Electron transfer between horse heart and Candida krusei cytochromes c in the free and bound states

Electron transfer between horse heart and Candida krusei cytochromes c in the free and phosvitin-bound states was examined by difference spectrum and stopped-flow methods. The difference spectra in the wavelength range of 540–560 nm demonstrated that electrons are exchangeable between the cytochromes c of the two species. The equilibrium constants of the electron transfer reaction for the free and phosvitin-bound forms, estimated from these difference spectra, were close to unity at 20°C in 20 mM Tris-HCl buffer (pH 7.4). The electron transfer rate for free cytochrome c was (2–3) · 10⁴ M^?1 · s^?1 under the same conditions. The transfer rate for the bound form increased with increase in the binding ratio at ratios below half the maximum, and was almost constant at higher ratios up to the maximum. The maximum electron exchange rate was about 2 · 10⁶ M^?1 · s^?1, which is 60–70 times that for the free form at a given concentration of cytochrome c. The activation energy of the reaction for the bound cytochrome c was equal to that for the free form, being about 10 kcal/mol. The dependence of the exchange rate on temperature, cytochrome c concentration and solvent viscosity suggests that enhancement of the electron transfer rate between cytochromes c on binding to phosvitin is due to increase in the collision frequency between cytochromes c concentrated on the phosvitin molecule.     

Role of hydroxyproline-rich cell wall protein in growth regulation of rice coleoptiles grown on or under water

The elongation of both intact and excised rice coleoptiles waspromoted when they were submerged in water. Amino acid analysisof the cell wall revealed that air-type coleoptiles (grown onthe surface of water) contained more hydroxyproline than water-typeones (grown under water). The suppression of hydroxylation ofpeptidyl proline under water was confirmed with air-type sectionsby examining the imino acid content, ¹⁴C-proline incorporationinto the cell wall and its modification by ,'-dipyridyl. Also,dipyridyl significantly promoted the growth of floated sectionsto the level of submerged sections. Therefore, the lower hydroxyprolinecontent caused by lower oxygen tension in water is concludedto be one of the factors promoting growth of rice coleoptilesunder water. However, the hydroxyproline content in the cellwall decreased with growth of both air-and water-type coleoptiles;thus hydroxyproline-rich cell wall protein can not be regardedas the final growth cessation factor in rice coleoptiles. (Received December 17, 1979; )     

Biosynthesis of triterpenoids from amino acids in Pisum sativum. The distribution of the radioactivity in squalene biosynthesized from radioisotopically labelled l-leucine and l-valine

Radioisotopically labelled l-leucine and l-valine were fed to Pisum sativum and incorporated into squalene and β-amyrin. Chemical degradation of the radioactive squalene revealed an equal distribution of the radioactivity in the isopentenyl pyrophosphate(IPP)-derived and the 3,3-dimethylallyl pyrophosphate(DMAPP)-derived moieties of the squalene molecule, unlike the unbalanced distribution in favour of the DMAPP-derived moiety of a monoterpenoid molecule biosynthesized from these amino acids by higher plants.     

Control of passive permeability of chinese hamster ovary cells by external and intracellular ATP

External ATP causes passive permeability change in several transformed cells, but not in untransformed cells. We studied the effect of external ATP on the passive permeability of CHO-K1 cells, a transformed clone of Chinese hamster ovary cells. Treatment of the cells with external ATP alone did not produce a permeability change, and this was observed only when a mitochondrial inhibitor, such as rotenone or oligomycin, was present together with ATP. These inhibitors reduced the concentration of intracellular ATP and a permeability change by external ATP was observed when intracellular ATP was decreased more than 70%. This requirement for permeability change of CHO-K1 cells was quite unique, since passive permeability change of other transformed cells so far tested was induced by ATP alone. Treatment of CHO-K1 cells with cyclic AMP analogues increased their sensitivity to external ATP about 2-fold. The roles of external and intracellular ATP in controlling passive permeability are discussed.     

Studies on the population dynamics of a thistle-feeding lady beetle,Henosepilachna pustulosa (Kôno) in a cool temperature climax forest

1. A field study was carried out on the population dynamics of a thistle-feeding lady beetle, Henosepilachna pustulosa (Kôno ) living in a cool temperature climax forest in northern Kyoto Prefecture, central Japan.
2. Intensive marking, release and recapture program was carried out to estimate the adult population parameters by usingJolly-Seber method.
3. Sampling ratio was around 50%. Marking ratio rapidly rised as the census progressed and approached to 100%.
4. Sex ratio (% ♀) was 63–69% in both overwintered and new adults.
5. Daily survival rate was as high as 0.95 or more and constant throughout the season. Adult longevity in the spring was longer than 40 days.
6. Reproductive rate i. e., the ratio of the number of newly emerged adults in a given generation to that of overwintered adults in the preceding generation, is very small, ranging 1–3, whereas winter survival is higher than 50%, consequently the size of populations in the study area remain in a remarkably constant size and it never reached a level where intraspesific competition occurred.
7. The population characteristics of H. pustulosa are compared with those of the two closely related species, H. vigintioctopunctata and H. vigintioctomaculata, which are the pests of Solanaceous crops. Hp is more K-strategic than the two pest species.

     

Triterpenoid saponins from Fatsia japonica

Five triterpenoid saponins isolated from the flowers, the mature fruits and the leaves of Fatsia japonica were identified as 3-O-[β-d-glucopyranosyl(1→4)-β-d-glucopyranosyl]-hederagenin (1), 3-O-[β-d-glucopyranosyl-(1→4)-α-l-arabinopyranosyl]-oleanolic acid (2), 3-O-[α-l-arabinopyranosyl]-hederagenin (3), 3-O-[β-d-glucopyranosyl]-hederagenin (4) and 3-O-[β-d-glucopyranosyl(1→4)-α-l-arabinopyranosyl]-hederagenin (5). The saponins 1 and 2 are new, naturally occurring, triterpenoid saponins. The distribution of the five saponins in three parts of the plant was investigated. Saponins 2, 3 and 5 were present in the flowers, saponins 1, 3, 4 and 5 were in the mature fruits and saponins 2, 3, 4 and 5 were in the leaves.     

Contact-mediated changes in ATPase activity at the surface of primary cultured hepatoma cells

Summary Hepatoma cells grown in monolayer culture display certain alterations in their Mg-ATPase activity present on the cell surface as a function of time during a exponential growth. Levels of enzyme estimated biochemically and expressed as activity per cell increase as the cell population density increases. Histochemical investigation shows that Mg-ATPase activity is located intensively on the surface of cell contact and the activity is not encountered on the cell surface facing the free space. No enzyme activity is detected histochemically on the cell surface of sparse culture. Deposits of acidic polysaccharide are also seen on the surface of cell contact.