SPATIAL-DISTRIBUTION OF TURGOR AND ROOT-GROWTH AT LOW WATER POTENTIALS

Spatial distributions of turgor and longitudinaL growth were compared in primary roots of maize (Zea mays L. cv FR27 x FRMol7) growing in vermiculite at high (-0.02 megapascals) or low (-1.6 megapascals) water potential. Turgor was measured directly using a pressure probe in cells of the cortex and stele. At low water potential, turgor was greatly decreased in both tissues throughout the elongation zone. Despite this, longitudinal growth in the apical 2 millimeters was the same in the two treatments, as reported previously. These results indicate that the low water potential treatment caused large changes in cell wall yielding properties that contributed to the maintenance of root elongation. Further from the apex, longitudinal growth was inhibited at low water potential despite only slightly lower turgor than in the apical region. Therefore, the ability to adjust cell wall properties in response to low water potential may decrease with cell development.