Download Mixing within cells: Cytoplasmic Streaming in Chara Corallina and

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)