Kinetics of Adaptation to Osmotic Stress in Lentil (Lens Culinaris Med.) Roots

When intact roots of lentil (Lens culinaris Med.) are subjected to severe osmotic stress by treatment with a solution of low water potential, they immediately begin to shrink. Within 10 to 15 minutes, shrinkage ceases, and within 20 minutes, the roots resume growth. The time lag between application of osmoticum and resumption of growth varies from about 10 to 30 minutes over the range of external water potentials of -2 to -12.4 bars. For external water potentials as low as -8.7 bars the new steady rate of growth in the presence of osmoticum is approximately equal to that prevailing before application of osmoticum. For external water potentials between -8.7 and -13 bars growth resumes, but the new rate is less than that prior to addition of osmoticum. Measurements of changes in the internal solute content during adaptation show that the solute content of the root increases but that the magnitude of the increase is, by itself, insufficient to account for the resumption of rapid growth.