Chemiosmotic coupling of ion transport in the yeast vacuole: Its role in acidification inside organelles

Acidification inside the vacuo-lysosome systems is ubiquitous in eukaryotic organisms and essential for organelle functions. The acidification of these organelles is accomplished by proton-translocating ATPase belonging to the V-type H⁺-ATPase superfamily. However, in terms of chemiosmotic energy transduction, electrogenic proton pumping alone is not sufficient to establish and maintain those compartments inside acidic. Current studies have shown that thein situ acidification depends upon the activity of V-ATPase and vacuolar anion conductance; the latter is required for shunting a membrane potential (interior positive) generated by the positively charged proton translocation. Yeast vacuoles possess two distinct Cl^– transport systems both participating in the acidification inside the vacuole, a large acidic compartment with digestive and storage functions. These two transport systems have distinct characteristics for their kinetics of Cl^– uptake or sensitivity to a stilbene derivative. One shows linear dependence on a Cl^– concentration and is inhibited by 4,4-diisothiocyano-2,2-stilbenedisulfonic acid (DIDS). The other shows saturable kinetics with an apparentK _m for Cl^– of approximately 20 mM. Molecular mechanisms of the chemiosmotic coupling in the vacuolar ion transport and acidification inside are discussed in detail.     

Autotrophic picoplankton in southern Lake Baikal: abundance, growth and grazing mortality during summer

Autotrophic picoplankton were highly abundant during the thermalstratification period in late July in the pelagic area (waterdepth 500–1300 m) of southern Lake Baikal; maximum numberswere 2 x 10⁶ cells ml^–1 in the euphotic zone ({small tilde}15m). Unicellular cyanobacteria generally dominated the picoplanktoncommunity, although unidentified picoplankton that fluorescedred under blue excitation were also abundant (maximum numbers4 x 10⁵ cells ml^–1) and contributed up to {small tilde}40%of the total autotrophic picoplankton on occasions. Carbon andnitrogen biomasses of autotrophic picoplankton estimated byconversion from biovolumes were 14–84 µg C l^–1and 3.6–21 µg N l^–1. These were comparableto or exceeded the biomass of heterotrophic bacteria. Autotropicpicoplankton and bacteria accounted for as much as 33% of paniculateorganic carbon and 81% of nitrogen in the euphotic zone. Measurementsof the photosynthetic uptake of [^l4C]bicarbonate and the growthof picoplankton in diluted or size-fractionated waters revealedthat 80% of total primary production was due to picoplankton,and that much of this production was consumed by grazers inthe <20 µ.m cell-size category. These results suggestthat picoplankton-protozoan trophic coupling is important inthe pelagic food web and biogeochemical cycling of Lake Baikalduring summer.     

MOLECULAR PHYLOGENETIC ANALYSIS OF rbcL IN THE PRYMNESIOPHYTA1

The nucleotide sequences of rbcL genes encoding the large subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) were determined from six species of Prymnesiophyta to clarify their phylogenetic relationships. Molecular phylogenetic trees were constructed using PAUP (Phylogenetic Analysis Using Parsimony). These analyses suggest that the Prymnesiophyta, except for the Pavlovales, area relatively stable monophyletic group. Pleurochrysis carterae, included in the Isochrysidales, is a sister species of a monophyletic group consisting of other members of the Isochrysidales, Gephyrocapsa oceanica and Emiliania huxleyi, members of the Coccosphaerales, Calyptrosphaera sphaeroidea and Umbilicosphaera sibogae var. foliosa, and a member of the Prymnesiales, Chrysochromulina hirta. The nucleotide sequence of rbcL from G. oceanica was identical to that from E. huxleyi within the region examined. Our trees show that G. oceanica and E. huxleyi are more closely related to C. hirta than to U. sibogae, C. sphaeroidea, and P. carterae. These results suggest that orders in the Prymnesiophyceae, including the above-mentioned genera, should be redefined.     

Genetic interaction between the Ras-CAMP pathway and the Dis2s1/Glc7 protein phosphatase in Saccharomyces cerevisiae

The Saccharomyces cerevisiae DIS2S1/GLC7 gene encodes a type 1 protein phosphatase indispensable for cell proliferation. We found that introduction of a multicopy DIS2S1 plasmid impaired growth of cells with reduced activity of the cAMP-dependent protein kinase. In order to understand further the interaction between the two enzymes, a temperature-sensitive mutation in the DIS2S1 gene was isolated. The mutant accumulated less glycogen than wild type at the permissive temperature, indicating that activity of the Dis2s1 protein phosphatase is attenuated by the mutation. Furthermore, the dis2s1 ^ts mutation was shown to be suppressed by a multicopy plasmid harboring PDE2, a gene for cAMP phosphodiesterase. These results indicate that the Ras-cAMP pathway interacts genetically with the DIS2S1/GLC7 gene.     

Accumulation of Phenylpropanoids in Cotyledons of Morning Glory (Pharbitis nil) Seedlings during the Induction of Flowering by Poor Nutrition

Flowering of Pharbitis nil strain Violet is induced in continuouslight under poor nutritional conditions. High-performance liquidchromatography of extracts of the cotyledons revealed that twocompounds in addition to chlorogenic acid accumulate under suchconditions. The compounds were identified as pinoresinol glucosideand p-coumaroylquinic acid. The endogenous levels of these phenylpropanoidswere correlated with the flowering response when nutrition waspoor. However, activation of phenylpropanoid biosynthesis seemednot to be essential for the induction of flowering. (Received May 17, 1993; Accepted July 26, 1993)     

A Factor That Interrupts the Cell Cycle at G2 or Prophase is Present in Full-Grown Frog Oocytes

Full-grown amphibian oocytes that had been arrested at meiotic prophase I contained an activity that prevented the cell cycle from progressing beyond a G₂-like stage. Injection of the contents of germinal vesicles (GV-content) or cytoplasm obtained from oocytes of the frog Rana rugosa prevented fertilized eggs of Cynops pyrrhogaster or Bufo japonicus from cleaving. The nuclei in the arrested eggs consisted of thin chromosomes and nucleolus-like particles enclosed within clear nuclear membrane and their volume increased as a function of time after injection. Cycling of maturation-promoting factor (MPF) did not occur in the injected eggs, but DNA synthesis was not disturbed. The injection of exogenous MPF into the eggs induced the reinitiation of the cell cycle with progression to the M phase and subsequent cleavage. Furthermore, the injection into the full-grown oocytes of Bufo inhibited induction of the maturation of oocytes by progesterone. These results demonstrate that a factor that arrests the cell cycle either at a G₂-like stage of mitosis or at prophase in meiosis is present both in the GV and cytoplasm of frog oocytes. We refer to this factor as a G₂-specific cytostatic factor (G₂-CSF). G₂-CSF may play an important role not only in the physiological arrest at prophase I in meiosis, but also in regulation of the G₂/M transition in the cell cycle of early embryonic cells.     

Host plant conspicuousness and the distribution of eggs and larvae in the butterfly,Anthocharis scolymus (Lepidoptera: Pieridae)

We investigated how the distribution pattern of eggs and larval on the host plant, Turritus glabra, was influenced by the oviposition behavior of the pierid butterfly Anthocharis scolymus. Females searched for the host plants visually and they frequently approached taller host plants with sparse surrounding vegetation. After encountering host plants, oviposition behavior of females was independent of host plant characteristics such as height, density, and type of surrounding vegetation. A female laid eggs singly on a host plants. Most females appeared to lay their eggs regardless of the presense of eggs on the host plant. Consequently egg and larva tended to be abundant on conspicuous host plants as measured by height or relative isolation from other plants. However, overcrowding of eggs on an individual host decreased the survival rate of larvae.     

Water intake by the adult mayflyEpeorus ikanosis (Ephemeroptera: Heptageniidae) and its effect on their longevity

Water drinking habits during flight in adult mayflies ofEpeorus ikanonis Takahashi were observed and the effect of water intake on their longevity was examined. The study was carried out in a mountain stream in western Japan. Adult males collected a water droplet under the head capsule while alighting on the water surface and consumed it after moving to nearby riparian vegetation. The amount of water intake was experimentally estimated to be 9.7% of the bodyweight for males. Although females did not show the water drinking behavior in the field, they imbibed as much as 5.5% of the bodyweight of water in an experimental situation. Morphological observation of the mouthparts revealed that the water was drawn in through the pits at the base of the labrum. In the field caging experiment, males with a water supply had a substantially longer life span than those without. Increase in adult life span by drinking water was less marked in females. Multiple copulation was observed in both sexes during the experiment. The water drinking behavior of the males may closely relate to mating success through increased longevity. Variation in the longevity of adult mayflies was discussed with regard to the possibility of water intake. This paper forms part of a PhD thesis submitted to the Department of Zoology in Kyoto University (1990).