The growth parameters of Lockhart's equation were investigated for finding which component was predominantly contributing to the cell expansion rates of plants subjected to environmental stresses under tissue-culture conditions. Embryos isolated from soybean seeds were grown under tissue-culture conditions. The sizes of the water potential gradient between the water source and elongating cells correlated with the speed of growth rates under nutrient deficiency, salt stress, growth retardation, induced by plant growth regulators and trehalose, indicating that cell expansion rates were mainly associated with how much water could be absorbed by elongating cells regardless of the kinds of environmental stress conditions applied.