Plant Physiology (Biology 327) - Dr. Stephen G. Saupe; College of St. Benedict/ St. John's University; Biology Department; Collegeville, MN 56321; (320) 363 - 2782; (320) 363 - 3202, fax; ssaupe@csbsju.edu |
Water
Conductivity of Potato Tubers
Flux density, Js, is a measure of the volume of water crossing the membrane per
unit area per unit time. It is
expressed in units of m3 m-2
s-1 or simplified m s-1.
Lp is the hydraulic conductivity of the membrane (in units of m3 m-2
s-1 MPa-1 or simplified to m s-1 MPa-1)
which is a factor that relates permeability of the system to water flow.
Ultimately, the flow into (or out of) a system is a function of hydraulic conductivity. The driving force for transport is the water potential gradient. These factors can be mathematically expressed as: Js = Lp (ΔΨ).
Flux density and hydraulic conductivity can be calculated from our Gravimetric
data. However, we will also need to know the surface area of a core.
Procedure:
1. Set up the Gravimetric experiment. Measure
& record in Table 1 the diameter and length of the cores. Also
record the duration of the experiment (Table 1) and then complete the calculations.
2. Complete Table 2
Calculate the solution Ψs (MPa) from the van't Hoff equation (see Chardakov lab).
Obtain the water potential of the potato tubers (Ψtuber) from the Gravimetric experiment. Then, calculate ΔΨ (Ψsoln � Ψ tuber).
Transfer the change in weight data from the Gravimetric experiment (column 4) into column 4 (water uptake).
Calculate flux density
3.
Plot Js (m s-1) vs.
ΔΨ
(MPa).
4.
Calculate the slope of this line which will yield Lp = cm sec-1 MPa-1.
For potato, the expected values for L are 1.5 10-7 m MPa-1
s-1.
Table
1:
Core/Experimental Data |
|
average
core length (cm) |
|
average
core width (cm) |
|
average core surface area (cm2; 2 π r2 + 2 π r h ) | |
total
core surface area per treatment (surface area/core times the number of
cores per treatment; cm2 |
|
time
experiment start |
|
time
experiment end |
|
incubation
time for cores ( |
Table
2. Water Uptake by Potato
Tubers |
||||
[Sucrose]
(molal)
|
Ψsolution
(MPa) |
ΔΨ
(Ψsoln �
Ψtuber ; MPa) |
Water
Uptake (Final wt � Initial wt; cm3) |
Js
= flux density = (cm3 / (core SA in cm2 x time in
s) |
0 |
||||
0.1 | ||||
0.2 | ||||
0.3 | ||||
0.4 | ||||
0.5 | ||||
0.6 | ||||
0.7 |
References:
Barcelo,
AR, AA Calderon and R Munoz. 1994.
Measuring water conductivity coefficients in plant tissues.
Journal of Biological Education 28: 83 � 85.
| Top | SGS Home | CSB/SJU Home | Biology Dept | Biol 327 Home | Disclaimer | |
Last updated:
01/07/2009 � Copyright by SG
Saupe