Gravity-regulation of Cell Elongation in Nodes of the Grass Echinochloa colonum

Abstract

Summary A bending response to a gravitational stimulus in the nodes of the grass Echinochloa colonum is evoked within 35—45 min of their being placed horizontal. The bending is attributable to cell elongation which is initiated in the leaf sheath base when it is displaced from the vertical. If the nodes alone are excised, some elongation occurs in the normal vertical position, but when placed horizontally, elongation on the lower side is enhanced and on the upper side is reduced. The extent of cell elongation is thus regulated by the orientation of the node with respect to gravity, and can be related to the position of statoliths within the statocyte cells. Two models are proposed: the first is based on a positional sensitivity within the statocyte cells, the second depends on a positional association of the statocyte cells with adjacent bundle sheath cells.