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Mixing within cells: Cytoplasmic Streaming in Chara Corallina and its implications for intracellular transport. Chara corallina v. Australis Idan Tuval, JW Vd Meent, Ray Goldstein Aquatic vs land plantsproduction) Photosynthesis Growth Nutrients (energy (energy Uptake consumption) Chara corallina v. Australis The Discovery of Streaming Chara Internodal cell after osmotic stress Flow pattern (Digital Images from the British Library) Cytoplasmic Streaming (Cyclosis) • • Algae: Chara, Nitella, Acetabularia, … Rotational streaming Fluid-like circulation of cellular sap (cytoplasm) Steady velocities up to 100 µm/s Plants: (hair cells, pollen tubes): Tradescantia, Urtica, Cucurbita, … Circulation streaming Protozoa:Paramecium, Stentor, Allogromia, ... Multi-striate streaming The Mechanism of Streaming Tominaga et al, EMBO J, 2003 • • • Matthew L. Walker, Stan A. Burgess, James R. Sellers, Fei Wang, John A. Hammer III, John Trinick & Peter J. Knight. Two-headed Binding of a Processive Myosin to F-actin. Nature, 405, 804-807 (2000). Organelles coated with myosin are transported along actin filaments Kamitsubo/Shimmen (1994): Myosin XI purified from Chara/Lilys Robust under surgery: Ideal for studies on membrane transport Helical Circulation in Giant Internodal Cells Kamiya & Kuroda, Bot Mag Tokyo, 1956 1 cm Transport is advection-dominated Can high Pe flows aid homeostasis by enhancing mixing? 100 µm Streaming as a Hydrodynamic Problem Stokes flow in a cylinder: Downstream flow IZ+ IZ- Stream-function components IZ+ IZ- Solution of Vacuolar Flow Significant radial displacement over one helical period! Helicity of flow essential for radial transport and mixing Consequences for transport I: Fast radial redistribution Simplest measure of diffusion-limited exchange with vacuole Consequences for transport I: Fast radial redistribution Response-time for boundary layer dρ/dt at Center [-] Separation of typical timescales: Response-time for front Consequences for transport II: Homogenization of downstream transport Life in the “fast-line” t Kamiya et al. 1956 Mustacich et al. 1977 Stagnant region Relative standard deviation of downstream displacements tends to zero in a short length ξ ~ λ3. Consequences for metabolism I: Surface Inhomogeneity • Measurable through chlorophyll fluorescence as a proxy for photosynthesis at IZ+ and IZ- Consequences for metabolism II: Growth peak coincides with pitch minimum! Helical pitch and Growth rate P. B. Green, Am. J. Bot,1954 Experimental Verification: Magnetic Resonance Velocimetry of Chara Cross-sectional Profiles Average Profiles Work in progress: Magnetic Resonance Velocimetry: Injection of tracer particles: JW Vd Meent, AJ Sederman JW Vd Meent, C Picard Conclusions: Streaming enhances homeostasis • `Life at High Peclet numbers’: advection facilitates diffusion by carrying away the saturation layer surrounding a metabolically active object. Helical shear flow in a cylinder • Fast radial mass redistribution. • Enhanced mass flux across the boundary of the cell. • Homogenization of longitudinal advection. Goldstein, Tuval, van de Meent, PNAS 105, 3663 (2008) van de Meent, Tuval, and Goldstein, PRL 101, 178102 (2008)