Plant Physiology (Biology 327)
- Dr. Stephen G. Saupe; College of St. Benedict/ St.
University; Biology Department; Collegeville, MN 56321; (320) 363 - 2782;
(320) 363 - 3202, fax;
the Water Status of Potato Tubers
Upon completion of this laboratory you should be able to:
- determine the water potential of a plant tissue by the
techniques and understand the underlying theory.
- determine the osmotic potential of a plant extract by the
freezing point depression
method and understand the underlying theory.
- describe techniques for measuring the pressure potential of a plant tissue.
- describe techniques for measuring plant water status such as the pressure bomb, vapor
pressure osmometer, and psychrometer.
Water potential (Ψw,
psi), which is a measure of the energy state of water is affected by dissolved
solutes, pressure and matrix particles. The contribution to water potential by
dissolved solutes, termed osmotic potential (Ψs
), is always negative in sign. In other words, solutes decrease the
water potential. The contribution of pressure (Ψp)
may be positive, negative or zero, but is generally positive since most plant cells are
turgid (turgor pressure). The contribution due to the binding
of water to colloidal particles (matric) and surfaces, termed matric potential (Ψm),
also lowers the water potential. Although it is often small enough to be
ignored, matrix potential is important when considering
soil water relations. Thus, the water potential of a plant system can be
arithmetically represented by the equation:
Ψs + Ψp + Ψm
In this lab we will use the Chardakov and
techniques to determine the water potential (Ψw) of a potato tuber cells. We
will determine the solute potential (Ψs
) by the Freezing
Point Depression Method. Pressure in the cells can be arithmetically
calculated once Ψs and Ψw are
known. If time permits, we will also measure the water conductivity of
potato tubers, determine the Q10 for water transport into potatoes and prepare a
- Email to me before lab begins the
answers to questions 1-6 in the
- Print copies of this exercise and the following
handouts and bring them all to lab:
- Write an abstract of
- Append to your abstract the following (be
sure to include appropriate captions for your tables and graphs):
- Chardakov Tables 1 & 2.
Calculate the water potential of the potato based on these data.
- Gravimetric Table 2.
Plot % change in weight vs. [sucrose]; include best fit
line with regression analysis data. Calculate the water potential of the
potato based on these data. In your abstract discuss how the water
potential values obtained from the Chardakov and Gravimetric techniques
compare and which is likely most accurate.
- Freezing point Tables 1 & 2.
Plot temperature vs. time for both water
and sap on the same graph.
- In your abstract be sure to include: the
pressure (Ψp) in the potato cells and discussion whether the data
you collected supported your hypotheses.
- Barcelo, AR, AA Calderon and R Munoz
(1994) Measuring water conductivity coefficients in
plant tissues. Journal of Biological Education 28: 83 85.
- Bland, W. and C. B. Tanner (1985) Measurement of the water potential of stored potato
tubers. Plant Physiology 79: 891-895.
- Boyer, JS (1969) Measurement of the water status of plants.
- Koning, R (1999) Web Site:
- Kramer, P (1983) Water Relations of Plants. Academic Press, NY.
- Meidner, H (1984) Class Experiments in Plant Physiology. George Albert Unwin, Boston.
- Reiss, Carol (1994) Experiments in Plant Physiology. Prentice-Hall, Englewood Cliffs,
- Ross, C (1974) Plant Physiology Lab Manual. Wadsworth.
01/07/2009 � Copyright by SG