Understanding the physical basis of growth from the top...
24
Understanding the physical basis of growth from the top down. Siobhan (#2) Braybrook The Sainsbury Laboratory University of Cambridge [email protected] www.plantmechanome.org
Transcript of Understanding the physical basis of growth from the top...
Understanding the physical basis of growth from the top down.
Siobhan (#2) Braybrook The Sainsbury LaboratoryUniversity of Cambridge
[email protected] www.plantmechanome.org
Firas Bou Daher Marco Aita Lihua Han
Rozi VőfélyPhD student
Marina LinardićPhD student
Tom Torode
Summer Students:Ashley MantonAmy RobertsSimon Butterworth
Part II Plant Sci:Amish Gir
The Plant Mechanics Group
www.plantmechanome.org
How do plants grow shapes?
Understanding shape growth in plants
Biology Materials science
Organ Tissue
CellWall Components
Shape growth occurs on many scales because of actions on each scale
Understanding any given scale is not enough to explain the whole
Biophysics of plant cell growth
Cells grow and change shape by altering 2 parameters:
Changes in internal cell pressure
Changes in wall mechanicsAnisotropyElasticityViscosity
The plant cell wall is a complex biological composite
Pectins (gel matrix)Hemicellulose (tethers/struts)
Cellulose (fibers)
Creative Commons, `Ladyofhats`
Cell wall structure will change dynamically by alteration and addition of new material
Simple shape change: anisotropy
Polar organ growth in hypocotyls
Cell wall properties
Hormone biology
Endo/exocytosis
Wall chemistry
Cytoskeleton
pH and Ca++
Response to light
Response to gravity
Regulatory genes
Dark‐grown hypocotyls keep reaching for the surface: etiolation
Kinematics of hypocotyl etiolation
0
5000
10000
15000
0 4 8 12162024283236404448525660646872768084889296
Hypo
cotyl len
gth (m
m)
0
2.5
Time in hours
Kinematics of hypocotyl etiolation
0
5000
10000
15000
0 4 8 12162024283236404448525660646872768084889296
Hypo
cotyl len
gth (m
m)
0
2.5
Time in hours
Extreme oriented cell/organ growth during etiolation
germination
72h post germination
25 umX
13 um
500 umX
15 um
Cell expansion occurs in a Basal‐> Apical wave
0
500
1000
1500
2000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
Cell Area
(um)
Cell Number
0H‐C16H‐C112H‐C124H‐C1
Simple shape change: anisotropy
AnisotropyElasticityViscosity
What does MT/CesA orientation look like in isotropic hypocotyl cells?
MT orientation is correlated with expansion in later stages of etiolation
Basal cells, MAP4‐GFP Top cells, MAP4‐GFP
24h
Orientation measured with FibrilTool(A. Boudaoud)
Simple shape change: anisotropy
AnisotropyElasticity/viscoelasticity
Viscosity
Current methods for examining biophysical changes in plants
A
weight
Extensometer Indentation/AFM Swell/Shrink
Water IN
Water OUT
Hypocotyl length (mm)
22h 42h 48h 96h
NT
PMEI
PME
4.5
3.5
2.5
1.5
0.5
Changes in pectin matrix affect growth magnitude and character but not
anisotropy
Non transgenic
+PME +PMEI
‐elasticity +elasticity
If not pectin, then who?
• Developing better testing/modelling methods for viscoelasticity (hemicellulose? expansins?)
• Immunolocalizations for chemical changes in the cell wall
• RNA profiling of transcripts associated with growth changes
We do not know yet…….
Simple shape change: anisotropy
AnisotropyElasticity/viscoelasticity
Viscosity
What’s going on under there?
Pectin‐based cell wall softening to control growth magnitude
Wall mechanical asymmetry occurs before MT orientation
MT reorient and provide material anisotropy for extreme growth Exposure to light quickly
effects elasticity of the cell wall to halt expansion
Viscoelasticity? Hemicellulose?
So far, all of our information pertains to the epidermis……is that enough?
Acknowledgments
Firas Bou DaherMarco AitaLihua HanRozi VofelyMarina LinardicAmy RobertsSimon Butterworth
The Plant Mechanics Group
plantmechanome.org
Newton Trust
Trinity College
Funding
