Automorphosis of higher plants on a 3-D clinostat

On a three-dimensional (3-D) clinostat, various plant organs developed statocytes capable of responding to the gravity vector. The graviresponse of primary roots of garden cress and maize grown on the clinostat was the same as the control roots, whereas that of maize coleoptiles was reduced. When maize seedlings were grown in the presence of 10(-4 M) gibberellic acid and kinetin, the graviresponse of both roots and Shoots was suppressed. The corresponding suppression of amyloplast development was observed in the clinostatted and the hormone-treated seedlings. Maize roots and shoots showed spontaneous curvatures in different portions on the 3-D clinostat. The hormone treatment did not significantly influence such an automorphic curvature. When the root cap was removed, maize roots did not curve gravitropically. However, the removal suppressed the automorphic curvatures only slightly. On the other hand, the removal of coleoptile tip did not influence its graviresponse, whereas the spontaneous curvature of decapitated coleoptiles on the clinostat was strongly suppressed. Also, cytochalasin B differently affected the gravitropic and the automorphic curvatures of maize roots and shoots. From these results it is concluded that the graviperception and the early processes of signal transmission are unnecessary for automorphoses under simulated microgravity conditions. Moreover, the results support the view that the amyloplasts act as statoliths probably via an interaction with microfilaments. (C) 1998 COSPAR. Published by Elsevier Science Ltd.