[Sedimentable amyloplasts in Japanese weeping cherry].

In branches of the upright type of Japanese cherry reacting on the gravity stimulation, tension wood were formed by the action of gibberellin in the secondary xylem and caused negative gravitropism [correction of gravitorpism]. In the other hand, in branches of the weeping type of Japanese cherry, gibberellin was almost used for the elongation of the tip region and the shortage of gibberellin in the supporting tissue caused on the lack of tension wood. The weeping branches were unable to support their own weight and elongated to downward. It has already reported that both the upright and the weeping types of Japanese cherry have sedimentable amyloplasts in the endodermal starch sheath cells. In this study, the endodermal starch sheath cells were examined to investigate the cause of abnormal gravi-response in branches of the weeping type of Japanese cherry. Current-year branches of both the upright and the weeping types of Prunus spachiana were used as materials. The amyloplasts in the weeping type sedimented toward the base of the branches elongating upward and toward the apex in the branches elongating downward. In both cases, the sedimentation was toward the gravity vector. Then, the amyloplasts of the weeping branches were re-sedimentated toward the vector of gravity after changing branch position mechanically to upward, same as the upright type. In electron microscope studies, it was showed that amyloplasts had the lamella structure and the endodermal starch sheath cells were filled with large vacuoles. Moreover, endoplasmic reticulum, which was noticed in organelle relating to the graviperception, distributed to the cell periphery and was not locally. It was not showed the cell polarity [correction of polality]. The fine structures of the endodermal starch sheath cell of both types of cherry were similar. These results suggest that the abnormality of the gravi-response in the weeping Prunus trees is not due to the abnormal development of gravi-sensor.