PLANT WATER RELATIONS AND CONTROL OF CELL ELONGATION AT LOW WATER POTENTIALS

Recent developments in water status measurement techniques using the p sychrometer, the pressure probe, the osmometer and pressure chamber ar e reviewed, and the process of cell elongation from the viewpoint of p lant-water relations is discussed for plants subjected to various envi ronmental stress conditions. Under water-deficient conditions, cell el ongation of higher plants can be inhibited by interruption of water fl ow from the xylem to the surrounding elongating cells. The process of growth inhibition at low water potentials could be reversed by increas ing 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 i mportant regulating factor for cell elongation other than metabolic fa ctors. The concept of the growth-induced water potential was found to be applicable for growth retardation caused by cold stress, heat stres s, 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-d eficiency, nutrient deficiency, salt stress, cold stress and heat stre ss conditions is suggested.