Plant Water Relations and Control of Cell Elongation at Low Water Potentials

Recent developments in water status measurement techniques using the psychrometer, the pressure probe, the osmometer and pressure chamber are reviewed, and the process of cell elongation from the viewpoint of plant-water relations is discussed for plants subjected to various environmental stress conditions. Under water-deficient conditions, cell elongation of higher plants can be inhibited by interruption of water flow from the xylem to the surrounding elongating cells. The process of growth inhibition at low water potentials could be reversed by increasing the xylem water potential by means of pressure application in the root region, allowing water to flow from the xylem to the surrounding cells. This finding confirmed that a water potential field associated with growth process, i.e., the growth-induced water potential, is an important regulating factor for cell elongation other than metabolic factors. The concept of the growth-induced water potential was found to be applicable for growth retardation caused by cold stress, heat stress, nutrient deficiency and salinity stress conditions. In the present review, the fact that the cell elongation rate is primarily associated with how much water can be absorbed by elongating cells under water-deficiency, nutrient deficiency, salt stress, cold stress and heat stress conditions is suggested.