PARENT SESSION
Posters P2B Light, redox and metabolic regulation: Light Reactions. Abstracts (444-478)

New approaches to studies of cell cycle regulation of photosynthesis in algae. Ivan Setlik^{1, 2}, Eva Setlikova^{1, 2}, Zdenko Gardian², Radek Kana², Josef Komenda^{1, 2}, Vojtech Kasalicky^{1, 2}, Ondrej Prasil^{*,1, 2}, ¹ Institute of Microbiology AVCR, Trebon, Czech Republic² Institute of Physical Biology, Nove Hrady, Czech Republic

ABSTRACT- Photosynthetic apparatus of unicellular algae undergoes major structural rearrangements and functional changes during each diel cycle. These changes reflect tight regulation driven by varying metabolic requirements of different phases of the cell cycle. As a result, the cellular photosynthetic activities of synchronized algal cultures exhibit diurnal changes with amplitude of up to one order. Although these diel changes of photosynthesis have been subject to numerous studies, no generally accepted model of the underlying regulatory mechanism(s) exists. We will present detailed analysis of diel changes in photosynthetic activities and in structural properties of thylakoid membranes in the model green alga Scenedesmus quadricauda. In our studies we have employed several novel methodological approaches, including the fluorescence kinetic microscope equipped with chamber that allows monitoring changes in photochemical activities of single algal cell during the whole cell cycle. We will compare this "single cell approach" with the traditional measurements in bulk suspensions. Throughout the whole cell cycle the overall photosynthetic activities measured both by oxygen evolution and carbon incorporation are inversely proportional to the extent of nonphotochemical quenching. The minimum of photosynthesis occurs at the time of cell division when the acceptor side of Photosystem II undergoes major modifications, as judged by changes in thermoluminescence and decay kinetics of variable fluorescence. At the same time the susceptibility of the acceptor side of PSII to herbicides significantly decreases and unusual pattern of phosphorylation of PS II proteins is observed. The simultaneously measured activity of PS I does not show any major cell cycle modifications. The analysis of data from the mass spectrometry shows cell-cycle dependent changes in the oxygen consuming processes in light (respiration and Mehler reaction) that are proportional to the instantaneous photosynthetic activity. The results obtained with Scenedesmus will be compared with results from other model algae from different taxonomic groups and model of regulation of photosynthesis during the cell cycle will be presented.

KEY WORDS: regulation, photosynthesis, cell cycle, algae