ROLES OF OSMOTIC ADJUSTMENT AND TURGOR POTENTIAL IN LEAF-AREA EXPANSION

We examined the roles of turgor potential and osmotic adjustment in pl ant growth by comparing the growth of spring wheat (Triticum aestivum cv. Siete cerrors) and sudangrass (Sorghum vulgare var. Piper) seedlin gs in response to soil water and temperature stresses. The rates of le af area expansion, leaf water potential and osmotic potential were mea sured at combinations of 5 soil water potentials ranging from -0.03 to -0.25 MPa and 6 soil temperatures ranging from 14 to 36-degrees-C. Sp ring wheat exhibited little osmotic adjustment while sudangrass exhibi ted a high degree of osmotic adjustment. However, the rate of leaf are a growth for sudangrass was more sensitive to water stress than that o f spring wheat. These results were used to evaluate the relationship b etween growth and turgor potential. The modified Arrhenius equation ba sed on thermodynamic considerations of the growth process was evaluate d. This equation obtains growth rate as a function of activation energ y, enthalpy difference between active and inactive states of enzymes, base growth rate and optimum temperature. Analyses indicate that the m odified Arrhenius equation is consistent with the Lockhart equation wi th a metabolically controlled cell wall extensibility.