Physiological Studies of Mechanically Stimulated Motor Responses of Flower Parts. I. Characterization of the Thigmotropic Stamens of Portulaca grandifolora Hook

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Abstract
The stamens of P. grandiflora exhibit positive thigmotropism when gently touched or pushed. The bending response can be detected within < 1 s of stimulation and is complete after 2-5 s, averaging 23.degree. in that time. The response, which is not dependent on the presence of the style, can be stopped by touching the other side of the stamen. If stimulated stamens on 1 side of the flower have moved, subsequently stimulated stamens on the other side of the flower will not respond. After moving, stamens take about 5 min to return to their original position and 6-8 min to recover full ability to respond again. The response of the stamens is greatest in the afternoon and is modulated by temperature with a Q10 of 1.98, but not by light. Respiratory inhibitors block thigmotropism, and exogenous ATP enhances it, suggesting a role for ATP as a native energy source for the response. A high level of exogenous auxin inhibits the response, as does ethrel. Exogenous c[cyclic]AMP and cGMP produce opposite effects.