Search results
(1 - 2 of 2)
- Title
- Cytometric quantification of nitrate reductase by immunolabeling in the marine diatom Skeletonema costatum,
- Description
- Background: The uptake of nitrate by phytoplankton is a central issue in biological oceanography due to its importance to primary production and vertical flux of biogenic carbon. Nitrate reductase catalyzes the first step of nitrate assimilation, the reduction of NO'3 to NO 2. A cytometric protocol to detect and quantify relative changes in nitrate reductase (NR) protein content of the marine centric diatom Skeletonema costatum is presented. Methods: Immunolabeling of NR protein was achieved with polyclonal antibodies raised against S. costatum NR. Antisera specific to a NR protein subunit and to a NR polypeptide sequence were compared and cytometric results of NR protein abundance were related to Western analyses. Changes in cellular NR abundance and activity were followed during an upwelling simulation experiment in which S. costatum was exposed to a shift from ammonia to nitrate as major nitrogen source. Results: NR protein could be detected in NO 3-grown cells and at extremely low levels hardly discernible by Western Blot densiometry in NH 4-grown cells. The protocol allowed observation of early stages of NR induction during an upwelling simulation. NR abundance increased after the nutrient shift to reach a new physiological 'steady- state' 96 hrs later. NR activity exhibited diel variation with maxima at mid- day. NR abundance as estimated by both flow cytometry and Western analysis exhibited a hyperbolic relationship to NR activity. This pattern suggests post-translational activation of NR protein. Conclusions: The presented protocol allows the differentiation of NH 4- versus NO 3-grown algae as well as the monitoring of early stages in the induction of nitrate assimilatory capacities. (C) 2000 Wiley-Liss, Inc., Cited By (since 1996):8 Seaweeds, CODEN: CYTOD, ,
- Author
- Jochem, Smith, Gao, Zimmerman, Cabello-Pasini, Kohrs, Alberte
- Date
- 2000-01-01T00:00:00Z
- Title
- Top-down impact through a bottom-up mechanism. In situ effects of limpet grazing on growth, light requirements and survival of the eelgrass Zostera marina,
- Description
- Temporal changes in abundance, size, productivity, resource allocation and light requirements of a subtidal eelgrass (Zostera marina L.) population were followed for 2 yr after the September 1993 appearance of a previously rare oval form of the commensal limpet Tectura depicta (Berry) in Monterey Bay, California, USA. By exclusively targeting the epidermis, limpet grazing impaired photosynthetic performance but left respiratory demand, meristematic growth and more than 90% of the leaf biomass intact. The resulting low P:R ratios of grazed plants raised the light requirements for the maintenance of positive carbon balance almost 2-fold relative to healthy ungrazed plants and prevented the summertime accumulation of internal carbon reserves. Shoot density in this once-continuously vegetated 30 ha meadow declined from more than 50 shoots m-2 (2230 g fresh wt [FW] m-2) to sparse patches supporting an average of 16 shoots m-2 (380 g FW m-2). More than 50% of the continuously vegetated meadow was converted to bare sand despite ambient light availability and water temperatures that were favorable for growth of healthy, ungrazed plants. Plant size declined by 50 % and internal sugar reserves declined more than 4-fold within 6 mo after the appearance of T. depicta. Plant losses were most extensive during winter, when internal carbon reserves were minimal. The dramatic decline in eelgrass vigor and abundance reported here, despite a physical environment that was favorable for healthy eelgrass survival, illustrates the amplification of top-down control by this relatively inconspicuous limpet through a feeding mechanism that specifically impairs photosynthesis, a bottom-up process., Cited By (since 1996):11, Seaweeds, CODEN: MESED, ,
- Author
- Zimmerman, Steller, Kohrs, Alberte
- Date
- 2001-01-01T00:00:00Z