A Dielectric Study of the State of Water in Plant Stems

Abstract

Pissis, P., Anagnostopoulou-Konsta, A. and Apekis, L. 1987. A dielectric study of the state of water in plant stems.—J. exp. Bot. 38: 1528-1540. We report on thermally stimulated depolarization current (TSDC) measurements on plant stems of six different species in the temperature range of 77-300 K and over a wide range of water contents, in an attempt to determine the binding modes of water molecules. The measurements revealed the existence of three dielectric dispersions. The first dispersion at low temperatures is attributed to the reorientation of loosely bound water molecules. The origin of the second dispersion at intermediate temperatures is not yet clear. It is either due to the reorientation of tightly bound water molecules or to the relaxation of some botanical materials rather than water. Finally, the third dispersion, at high temperatures, is attributed to water-assisted space charge polarization connected with dc ionic conductivity. The amount of tightly bound water is estimated to be about 0-2 g g~1 of dry material or about 30% of the total water content, the rest being mainly loosely bound water. Little or none of the water behaves dielectrically like pure water. Key words—Free and bound water, dielectric properties, water content. Correspondence to: National Technical University of Athens, Physics Department, Zografou Campus, 15773 Athens, Greece.