Effects of Chlorpromazine on Gravitropism in Avena Coleoptiles

Abstract

Chlorpromazine (CPZ), an inhibitor of the calcium-activated form of calmodulin, is readily taken up by the roots of intact oat seedlings but poorly translocated from the roots to the coleoptile of these plants. However, plants repeatedly rotated through solutions containing low concentrations of CPZ (10−8–10−5M) are infiltrated, and under these conditions, CPZ significantly inhibits the negative gravitropic response of the coleoptile without retarding elongation growth. This effect is observable in ‘decapitated’ (apical 1–2 mm removed) coleoptile sections and in intact whole coleoptiles. If exogenous auxin is supplied to the decapitated sections, both their growth rates and gravitropic responsiveness are increased and, under these conditions, CPZ can reduce the gravitropic curvature without reducing the overall growth rate. These results are discussed in relation to the possible role of calmodulin-dependent calcium-ion pumps in gravitropism.