ゲノム情報科学研究教育機構  アブストラクト
Date July 22, 2008
Speaker Dr. Oliver Ebenhoh, Max-Planck-Institute for Molecular Plant Physiology, Germany
Title Modeling the degradation of transitory starch in plant leaves
Abstract During daytime, plants draw energy from the sunlight through their photosynthetic apparatus which is located in the chloroplasts in leaf cells. A part of this energy is stored in the form of starch inside the chloroplasts and is degraded in the absence of light to provide energy for biomass accumulation and other vital processes. Despite the importance of this pathway, attempts to develop mathematical models are still sparse. One of our research activities lies in the development of such models for specific aspects of the degradation pathway.

Because starch is insoluble, the initial steps of the mobilization takes place at the physical interface of the starch granules and the chloroplastic bulk phase. While many enzymes involved in these initial degradation steps have been identified, many detailed aspects are still poorly understood. The insoluble nature of starch also necessitates new modeling approaches since starch cannot be treated as a metabolite in the usual sense. We have developed a mathematical model that takes the two-dimensional nature of the reaction space into account.

The enzymatic attack on the granule surface facilitates the release of glucans of different chain lengths. These are subsequently split into maltose units which are exported into the cytosol. A key enzyme required for the breakdown of odd-length glucan chains, the disproportionating enzyme, shows interesting properties when studied in isolation. We have developed a theoretical framework describing the entropic nature of the driving forces of this enzyme. Our investigations give rise to sepculations about the physical role of that enzyme also in the process of starch synthesis.
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