木薯淀粉累积途径及关键基因.ppt

Sucrose transport, loading and unloading model in cassava Haiyan Wang Institute of Tropical Bioscience Biotechnology (ITBB), Chinese Academy of Tropical Agricultural Sciences(CATAS) GCP21-II, Kampala, Uganda June 19, 2012 background source transport sink Sugar transport is important for starch synthesis in aspect of coordination source and sink. Phloem loading: assimilates enter into Sieve element-companion cell complex from mesophyll cell. Phloem unloading: assimilates transfer from se/cc complex to sink tissue. C Sugar transport strategy: A D B Symplasmic pathway: driven by downhill concentration gradient and depending on high plasmodesmal densities . Apoplasmic pathway: across plasma membrane driven by sugar transporters . Symplasmic loading in leaf Apoplasmic loading in leaf Apoplasmic unloading in sink cell Symplasmic unloading in sink cell Sucrose transporter Membrane-localized, energy-dependent, H+-symporting sucrose transporters (SUC or SUT). Type 1, high affinity, low capacity; Type 4, lower affinity，high capacity; Type 2, lower affinity, for sucrose sensor; Cell wall invertase (CWI) and sucrose synthase (SuSy) involve in sucrose transport coherent with apoplasmic and symplasmic transport respectively. (Arnd Sturm, 1999) Symplasmic transport Apoplasmic transport Enzymatic activity mRNA expression Ultrastructure of SE-CC complex Fluorescent tracing autoradiography Immunolocalization immunobloting SUT、CW-INV、V-INV、SUSY Sugar component in phloem sap of Arg7 stem Fructose Glucose Sucrose Sucrose is the main component, it’s concentration is about 570mg/ml, indicating that sucrose is the form of sugar transport in cassava. Plasmodesmal density of phloem SE-CC complex and adjacent cells in leaf SE sieve element; CC companion cell PD plasmodesmata; PC parenchyma cell BS bundle sheath cell PD SE cc cc PD PC PC PC CC PP SE BS cc cc cc SE SE BS PC BS BS BS SE A B C A moderate number of plasmodesmata distributed between SE-CC complex and adjacent