The effect of mechanical impedance on root growth in pea (Pisum sativum).: II.: Cell expansion and wall rheology during recovery

The aim of the present work was to determine the factors limiting growth in mechanically impeded roots, Pea roots were grown in compressed and uncompressed sand cores, and then removed and transferred to hydroponics, Root elongation was slowed in impeded sand cores and did not recover to the unimpeded rates until 60 h after transfer to the hydroponics system. Root diameter was greater in impeded roots, and only after 36 h in hydroponics was new root tissue produced of the same diameter as the unimpeded controls, The turgor pressure of the growing cells was measured with a turgor probe and was the same in both treatments. The slower elongation rate of the previously impeded roots was, therefore, the result of axial tightening of the cell walls, Cell length profiles suggested that axial cell wall tightening persisted in the unrestricted hydroponics system. Production of new cells in unrestricted conditions was required before root elongation returned to the unimpeded state. Osmotic potential was decreased by approximately 0.2 MPa in previously impeded roots compared with the unimpeded ones. This corresponds to a decrease in water potential of 0.2 MPa, These data are discussed in relation to regulation of cell extension, solute unloading and the penetration of compacted soils by roots.