1990

mardi 21 avril 2009
par   G. Grégori

Armbrust EV, Chisholm SW (1990) Role of Light and the Cell-Cycle on the Induction of Spermatogenesis in a Centric Diatom. Journal of Phycology 26 :470-478

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The centric diatom, Thalassiosira weissflogii Grun., can be induced to undergo spermatogenesis by exposing cells maintained at saturating levels of continuous light to either dim light or darkness. Using flow cytometry to determine the relative DNA and chlorophyll content per cell, the number of cells within a population that responded to an induction signal was measured. From 0 to over 90% of a population differentiated into male gametes depending upon both the induction trigger and the population examined, regardless of the average cell size of the population. Through the use of synchronized cultures, we demonstrated that responsiveness to an induction trigger was a function of cell cycle stage ; cells in early G1 were not yet committed to complete mitosis and were induced to form male gametes, whereas cells further along in their cell cycle were unresponsive to these same cues. A simple model combining the influence of light on the mitotic cell cycle and on the induction of spermatogenesis is proposed to explain the observed diversity in population responses to changes in light conditions.


Burkill PH, Mantoura RFC (1990) The Rapid Analysis of Single Marine Cells by Flow-Cytometry. Philosophical Transactions of the Royal Society of London Series a-Mathematical Physical and Engineering Sciences 333 :99-112

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Wood AM, Townsend D (1990) DNA Polymorphism within the Wh7803 Serogroup of Marine Synechococcus Spp (Cyanobacteria). Journal of Phycology 26 :576-585

<Go to ISI> ://A1990EU78500024

Genetic differences among ten strains of chroococcoid cyanobacteria (Synechococcus spp.) were identified by Southern blot hybridization. Data on shared number of restriction fragment length polymorphisms were used to identify the pattern and degree of genetic relatedness among the strains by two different methods of phylogenetic analysis. All the marine strains in the study contained phycoerythrin (PE) and cross-reacted with antisera directed against strain WH7803. Five contained a PE composed of phycourobilin (PUB) and phycoerythrobilin (PEB) chromophores, and three contained a PE composed of only PEB chromophores. Two freshwater strains which do not contain PE and do not cross-react with the anti-WH7803 serum were included in the study for comparison. Dollo Parsimony analysis and cluster analysis showed that the WH7803 serogroup includes at least four widely separated genetic lineages. Strains within each lineage were closely related but the differences between lineages were as great as those between any of the marine lineages and the freshwater lineage. Strains cultured simultaneously from the same water mass were associated with different lineages. Thus, we conclude that natural assemblages of marine Synechococcus are, at least occasionally, composed of individuals as genetically distinct from each other as members of different species or genera in other taxa.


Yentsch CM (1990) Environmental health : flow cytometric methods to assess our water world. Methods Cell Biol 33 :575-612

http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=2084485

Flow cytometry/cell sorting in aquatic sciences has been driven in two directions. The frontier directions are on shipboard and shore-based. On the one hand, the rapid analytical technique has been taken on shipboard to provide a real-time assessment of the particles and phytoplankton in water masses. These data also give information on the amount of vertical mixing and advection, and denote fronts between two or more water masses. There is an optical characterization (based on sizes, numbers, and pigment groups) of the individual primary producers, as well as detritus and suspended sediments. An optical-closure question is being addressed : "Does the total optical signal equal the sum of the parts ?" Additionally, associations with chemical and physical oceanographic features are readily accomplished. A "census" of thousands of phytoplankton cells is obtained and can be mapped. Scientists are able to identify "who is where ?" Such data are critical to understand the optical-feedback loop or the so-called photon-budget-in-the-sea, which in turn controls the rates at which growth processes occur in nature. On the other hand, an in-depth understanding is sought as to how particle size, shape, refractive index, nutritional status (nutrient and/or light limitation), growth dynamics, and cell cycle combine to control the optics (light scatter and fluorescence at the moment, and ideally absorption as well) or the photon-budget-of-the-cell. For this purpose, a shore-based facility associated with a diverse collection of phytoplankton is ideal. The development at Bigelow Laboratory of the Jane J. MacIsaac Facility is to provide services for the oceanographic community. Association and co-location with the Provasoli-Guillard Center for Culture of Marine Phytoplankton is key. Visitors are trained and given access to state-of-the-art instrumentation. Visiting investigators have available "the tropical, temperate, and polar seas" in concentrated form, as marine phytoplankton isolated worldwide and maintained as living clonal cultures. In this way, frontline cell biology questions can be addressed. The relentless exploration of standards and controls appropriate for the aquatic community must be continued. An intercalibration effort is a vital step. It is only with the widespread acceptance of particular reference materials and uniform optical filters among research groups utilizing FCM that comparable data sets describing aquatic particle distributions will be possible. For a global science, this strategy is imperative.