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Size-dependent changes in phytoplankton C and N uptake in the dynamic mixed layer of Lake Biwa (1996)

FRENETTE, JEAN-JACQUES ; VINCENT, WARWICK ; LEGENDRE, LOUIS ; [et al.]

Oxford BSL : Blackwell Science Ltd

Freshwater biology 36 (1996), S. 0

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ISSN: 1365-2427

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: 1. Short-term (days) hydrodynamic effects of wind-induced mixing on phytoplankton size structure, and C and N uptake characteristics, were studied in the surface mixed layer (epilimnion) of Lake Biwa (North Basin), before and during a period of high winds (typhoons).2. The latter period was characterized by two major typhoon events associated with deepening of the seasonal thermocline, reduced water column stability, decreased underwater irradiance and increased dissolved reactive N and particulate P.3. Nutrient concentrations, seston C/N ratios, and uptake rates indicated that phytoplankton biomass and production were limited by P and not N throughout the study. Higher C- and N-based productivity during the typhoon period than before reflected the increased phytoplankton biomass and higher specific uptake rates due to increased nutrient supply.4. Changes in the size-structure of phytoplankton (〈 2 and 〉 2 μm) were associated with variations in the stratification and mixing regime. When vertical stability was high (before the typhoons) concentrations of 〉 2 μm biomass (chlorophyll a, particulate organic C and N) were higher at the bottom of the mixed layer than at the surface whereas, when stability of the mixed layer was low (the typhoon period), the contribution of picoplankton (〈 2 μm) to total Chl a increased at the surface and decreased at the bottom following the first high winds.5. Photoadaptive adjustments of the phytoplankton provided further evidence of hydrodynamic control. The lower intracellular Chl a concentrations and C and N uptake efficiencies in the 〈 2 μm fraction suggest that they experienced, on average, higher irradiance than the larger cells because of their lower sinking rates. During the stability period, picoplankton exhibited higher photosynthetic efficiencies at the bottom of the mixed layer than at the surface. Such differences disappeared during the typhoon period indicating that the mixing rate was then probably higher than the photoacclimation rate in the small size fraction.6. The present results stress the highly transient nature of biological homogeneity in the surface mixed layer of the lake.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2427.1996.00083.x

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Physical mapping of the retinoid X receptorB gene in mouse and human (1995)

Nagata, Toshi ; Weiss, Elizabeth H. ; Abe, Kuniya ; [et al.]

Springer

Immunogenetics 41 (1995), S. 83-90

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ISSN: 1432-1211

Source: Springer Online Journal Archives 1860-2000

Topics: Biology , Medicine

Notes: Abstract Retinoid X receptors (RXRs) are zinc finger-containing nuclear transcription factors. They belong to the nuclear receptor superfamily that contains retinoid receptors, vitamin D receptors, thyroid hormone receptors, and steroid hormone receptors as well as the so-called orphan receptors. We previously mapped all three RXR genes on mouse chromosomes, using a panel of Mus spretus-Mus musculus interspecific backcross mice: Namely, the RXRA- gene (Rxra) on Chr 2 near the centromere, the RXRB gene (Rxrb) on Chr 17 in the H2 region, and the RXRG gene (Rxrg) on distal Chr 1. Using cosmid clones that cover the major histocompatibility complex (MHC) region, we determined the precise physical map positions of the gene encoding mouse and human RXRB, respectively. The mouse gene (Rxrb) maps between H2-Ke4 and H2-Ke5: namely, immediately telomeric to H2-Ke4 which encodes a histidine-rich transmembrane protein, and 12 kilobases centromeric to H2-Ke5 which is expressed in lymphoid tissues. Rxrb and H2-Ke4 are transcribed into opposite directions from a CpG-rich promoter of about 250 base pairs. This gene organization is well conserved also in the human genome at the HLA-DP subregion of CHr 6p, underscoring the strong conservation of the gene organization in the MHC region between the two mammals.