The lazy mutation in rice affects a step between statoliths and gravity-induced lateral auxin transport

Compared to wild type, the lazy mutant in Oryza sativa L. shows a reduced g ravitropic response. In order to locate the lesion in the stimulus-response chain, coleoptile segments of lazy rice were investigated with respect to auxin transport. Gravity-induced lateral movement of radiolabelled indoleac etic acid (IAA) was strongly inhibited by the lazy mutation compared to wil d type while uptake and longitudinal transport of IAA, as well as amyloplas t sedimentation, were not significantly affected. These findings suggest th at LAZY controls a step in the signalling chain between statoliths and auxi n secretion.