The distribution and redistribution of endoplasmic reticulum (ER) in geoperceptive cells.

Within the root cap in maize the cells believed to be responsible for the perception of gravity possess a rough-surfaced ER system with a distinctive pattern of distribution. The ER is found normally parallel to the nuclear membrane and to the walls, and symmetrically distributed. It can be disturbed from its parallel position by moving the root to any horizontal orientation, but it is not displaced by inverting the root into the 180° vertical position. On returning to the normal position of growth the ER rapidly reforms into the original symmetrical position. The implications of this position and movement and the possible role of the ER are discussed.