Notes on :Cosgrove, D. J., Van Volkenburgh, E., & Cleland, R. E. (1984: Stress relaxation of cell walls and the yield threshold for growth

1. Cosgrove, D. J., Van Volkenburgh, E., & Cleland, R. E. (1984): Stress relaxation of cell walls and the yield threshold for growth ATTACH

1 Cosgrove, D. J., Van Volkenburgh, E., & Cleland, R. E. (1984): Stress relaxation of cell walls and the yield threshold for growth ATTACH

1.1 Definition of Pressure, cell wall yield threshold in “Introduction”

[HY] Below statements are given without supporting references or experimental results

Absorption of water directly generates the increase in volume which is measured by most growth-measuring techniques and tends to restore P and \(\Psi\) towards their original values.
Under conditions of steady-state growth, stress relaxation of the cell wall because of loosening is balanced by an increase in wall stress because of water absorption by the cell, with the result that P remains constant.
The rate of cell extension is thought to be a function of the amount by which P exceeds the threshold value of turgor pressure required for growth (i.e. the “yield threshold”).

1.2 Observation

“The decrease in P in isolated apical segments (Fig 1) was most likely a consequence of stress relaxation of the growing cell wall.”

[HY] If the cell wall is alive and adding material, continued growth in volume will decrease the pressure
The observed decrease in pressure arises from the volume change, not the cell wall’s creep or stress relaxation.

1.3 High water potential meaning

“Water potential was higher (wetter)”

1.4 Notes for page 8

1.5 Claim: “In growing tissue, stress relaxation of the cell wall is an additional process, which may lower water potential of excised tissue.”

1.6 Experimental Setup

Pressure: Pressure Probe (Cosgrove and Cleland, 1983, Osmotic properties of pea stem internodes in relation to growth and auxin action, Plant Physiology, 72:332-338 )
Water potential: isopiestic psychrometer on excised stem segments
- [HY] it appears that this measured the water concentration and not the potential

1.7 Major Findings/Claims

1.7.1 Yield threshold for cell wall

[HY] The definition of “Yield threshold for cell wall” is not clear

1.7.2 Wall relaxation affects the water potential and turgor pressure of excised growing segments.

1.7.3 Solute release and absorption upon excision may influence

the water potential
turgor pressure of nongrowing excised plant tissues

1.8 Figures

1.8.1 Fig 1: Apical pea stem; Excision decreased P unless samples were kept in water

1.8.2 Fig 2: Basal pea stem; Excision dips but increases P

1.8.3 Fig 3: Apical pea stem; P decreases much faster in the IAA-treated tissue than in the water-treated tissue

“Time course for the relaxation in P was slower.”

[ ] IAA treatment: induce cell wall growth? Loosen cell wall?

1.8.4 Fig 4-6: Apical pea stem; Water potential; cell wall growth (or loosening) promotes the decrease in water potential

1.8.5 Fig 7: Basal pea stem; Water potential increases at a different rate but achieves a static value eventually

1.8.6 Fig 8: Apical pea stem; growth vs. osmotic pressure: Survival model graph

1.9 My critical questions

1.9.1 Growing cell wall: cell wall materials are being added:

Must involve the conservation of mass (continuity equation)
- \[\frac{\partial\rho}{\partial t} + \nabla\cdot\left(\rho\bm{v}\right)\]
- \[\frac{dM}{dt} = \frac{d}{dt}\int \rho dV = 0\]
Analysis should limit the range for an instantaneous moment or period where no cell wall material is added

Author: Hojae Y-i

Created: 2020-08-20 Thu 21:06

Validate

Mechanics of Food and Biological Materials

Yi' Research Group

Cosgrove et al. 1984