Measuring the Water Status of Potato Tubers
Measuring the Water Status of Potato Tubers
Objectives: Upon completion of this laboratory you should be able to:
1. determine the water potential of a plant tissue by the Chardokov and gravimetric techniques and understand the underlying theory.
2. determine the osmotic potential of a plant extract by the freezing point depression method and understand the underlying theory.
3. describe techniques for measuring the pressure potential of a plant tissue.
4. describe techniques for measuring plant water status such as the pressure bomb, vapor pressure osmometer, and psychrometer.
Introduction
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:
Ψw = Ψs + Ψp + Ψm
In this lab we will use the Chardakov and Gravimetric techniques to determine the water potential (Ψw) of a potato tuber cells. We will determine the solute potential (Ψs ) by the Freezing Point DepressionMethod. 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 Hofler diagram.
Pre-Lab:
1. Email to me before lab begins the answers to questions 1-6 in the
Objectives: Upon completion of this laboratory you should be able to:
1. determine the water potential of a plant tissue by the Chardokov and gravimetric techniques and understand the underlying theory.
2. determine the osmotic potential of a plant extract by the freezing point depression method and understand the underlying theory.
3. describe techniques for measuring the pressure potential of a plant tissue.
4. describe techniques for measuring plant water status such as the pressure bomb, vapor pressure osmometer, and psychrometer.
Introduction
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:
Ψw = Ψs + Ψp + Ψm
In this lab we will use the Chardakov and Gravimetric techniques to determine the water potential (Ψw) of a potato tuber cells. We will determine the solute potential (Ψs ) by the Freezing Point DepressionMethod. 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 Hofler diagram.
Pre-Lab:
1. Email to me before lab begins the answers to questions 1-6 in the
References: 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. ARPP 20:351-364. Koning, R (1999) Web Site: Osmosis Lab. 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, NJ. Ross, C (1974) Plant Physiology Lab Manual. Wadsworth.