Determination of water potential of potato tubers using gravimetric and Chardakov techniques1. INTRODUCTION: Water potential (W) is the measure of the free energy state of water in the plant cell, which is the driving force governing the movement of water into and out of the plant cell and affects various metabolic activities (O'Leary, 1970). ). Water potential depends on different solute concentrations, pressure, and the matrix of a particle; measured in Mega Pascal (MPa) and written as follows: W = s + p + mIn plants, dissolved solutes such as ions, sugars, proteins, amino acids and other substances decrease the availability of free energy and induce a solute potential ( S), having a negative value. Another factor affecting W is the pressure potential (P) which can be either positive for turgor cells, zero for flaccid cells, or negative for actively transpiring cells. Additionally, the binding of water to colloids which decreases the water potential is known as the matrix potential (m), it is often small and considered a component of the solute potential (Saupe), so for those convinced , it is ignored and now the equation is: W = s + p (1) Water potential can be determined by measuring the equilibrium vapor pressure, which can be measured by various methods based on different parameters for this purpose using gravimetric parameters (length, volume and weight) or using Chardakov methods. changes in specific gravity (O'Leary, 1970) or Chardakov pressure bomb chamber or determination of freezing point depression using hydrolytic pressure chambers or cryoscopic or oblioscopic methods, among others (Bland and Tanner, 1985). In this experiment, gravimetric and Chardakov techniques are used to determine the W of potato tubers by incubation in the middle of a paper...... of the water potential of stored potato tubers. Plant Physiology 79 (3), p 891-895. Available at: http://www.plantphysiol.org/content/79/3/891O'Leary JW (1970). A critical evaluation of the tissue immersion method for measuring plant water potential. Ohio J. of Sci., 70(1), p. 34-38. Available at: http://kb.osu.edu/dspace/handle/1811/5510 33 [Access date: April 12, 2014]Ros Barcelo A., Calderon A. and Munoz R. (1994). Measurement of water conductivity coefficients in plant tissues. Journal of Biological Education, 28 (2), p 83 – 85. from: http://www.tandfonline.com/doi/abs/10.1080/00219266.1994.9655371 [Access date: April 12, 2014] Saupe SG Measure l water status of potato tubers. St. John's University, Minnesota. [Online] Available at: http://employees.csbsju.edu/ssaupe/biol327/Lab/water/water-lab-intro.htm [Access date: April 12, 2014]