ABSTRACT
A number of factors like rubbing, bending, brushing, stroking, shaking, perturbation and seismic movements cause mechanical stress. The mechanical stress increased cytokinin activity in xylem exudate from sunflower roots, but directly diminished in the leaves, suggesting that stressed plants adapt to ensure a continued supply of cytokinins for growth and development. Decreased axial cell elongation and increased radial cell division occur in the internodes of mechanically perturbed or ethephon treated bean plants. The occurrence of mechanical stress-induced growth responses remote from the stimulus may relate to endogenous auxin levels. Depending on the point of mechanical stress application, elongating cells in the growth zone are inhibited because auxin is either depleted or is at supraoptimal level in that region. Mechanical stress inhibits stem elongation and induces radial thickening in pole bean plants. Moderately high amounts of applied LAA or abscisic acid at lower concentrations cause retardation of elongation similar to mechanical perturbation or exogenous ethephon application.
