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
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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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