Abstract
Plant organs display helical growth movements known as circumnutation. Circumnutation is considered to help plant organs find suitable environmental cues. We have revealed that the necessity of graviresponse for circumnutation using dicotyledonous plants such as Arabidopsis and morning glory. Although circumnutation is widely observed in land plant species, its mechanism in monocotyledonous plants is unknown. To investigate the relationship between graviresponsiveness and circumnutation in monocots, we used agravitropic mutant of rice, lazy1, and compared its circumnutation with that of wild-type. Coleoptile of wild-type rice showed obvious circumnutation when it was vigorously growing. On the other hand, the coleoptile of the lazy1 did not show obvious circumnutation despite the entire growth of coleoptile was similar to wild-type. These results suggest that circumnutation is closely related to gravitropic response. Furthermore, we found that treatment of an inhibitor of auxin efflux drastically reduced circumnutation in wild-type coleoptiles. Thus, it is suggested that circumnutation requires gravity-regulated auxin efflux in rice coleoptiles.
