Effects of Mechanical Stimulation on Avena Coleoptile Segment Elongation in a High Resolution, Continuous Growth-recording System

The effects of an abrasive mechanical stimulation of the inner epidermal surfaces of excised Avena coleoptile segments were examined in relation to growth in the presence and absence of exogenously supplied indole-3-acetic acid. Mechanical stimulation of this nature, provided immediately following excision, was found to elicit a small, transient increase in endogenous growth rate which contributed to a larger initial rapid growth response (previously referred to as a tactile response). These results, contrary to the earlier reports, suggest that the inner epidermal mechanical or tactile stimulation does not account for the entire initial rapid growth response. Preliminary experiments indicate that an alternative form of mechanical stimulation (segment excision) may contribute to that portion of initial rapid growth which is not attributable to inner epidermal abrasion.Following its initial growth-enhancing effect, inner epidermal stimulation had either no effect or in some cases appeared inhibitory to endogenous growth. Growth in response to exogenous auxin was appreciably inhibited by this form of mechanical stimulation.