Water potentials of Salsola kali L. at differing levels of substrate water availability

Abstract

Isolated embryos of Salsola kali L. (Russian thistle) were allowed to imbibe on filter paper in Peltier thermocouple psychrometer chambers with differing amounts of water available. Water potential determinations were made on the embryo-filter paper system periodically during the 24-h period of imbibition and early seedling growth. At the 24th h, complete extension of the embryonic axis occurred at an equilibrium water potential of -2 bars and an embryo water content of 114%, perceptible growth (uncoiling of the spiraled embryo) at -30 bars and 83%, and no growth or perceptible swelling at -54 bars and 56%. Hourly monitoring of the water potential of the plant-substrate system showed an initial rise toward a level that would be attained by the wetted filter paper alone and then a decline to lower water potential values at intermediate levels of water availability. This reversal is ascribed to the increasing effects of the osmotic and matric components of the total water potential of the plant tissue during imbibition and growth.