[Effect of inversion on the arrangement of the endoplasmic reticulum and the polarity of statocytes in roots of Lepidium sativum]

Abstract

Primary roots of Lepidium sativum (L.s.) grew upwards in glass capillaries in order to prevent mechanically the geotropic curvature. The central cap cells (statocytes) were investigated with regard to the polar arrangement of their organelles. After 20 minutes of inversion, which correspond to the latent period of L.s., only the amyloplasts have left their original position and sedimented at the proximal cell pole. All the other organelles, particularly the ER-complex located near the distal periclinal cell wall, remain stationary. After 2 hours of forced inversion, which correspond to the reaction time of L.s., a second ER-complex is visible in the proximal cell pole in addition to the distal ER-complex. The new proximal ER-complex originates underneath the sedimented amyloplasts. The number of stacked cisternae in the proximal ER-complex is still smaller than in the distal one. After 18 hours of forced inversion the number of proximal cisternae has increased and is almost equal to the number of cisternae in the distal ER-complex.The proximal ER-complex seems to be formed by the nuclear envelope. The new synthesis is induced by a long-time inversion. This supports the postulation that the contact between amyloplasts and an ER-complex is a condition of geoperception.