Comparison Study of Gravity-Dependent Displacement of Amyloplasts in Statocytes of Cress Roots and Hypocotyls

In this study, the kinetics of gravity-dependent movement of amyloplasts (statoliths) along root statocytes and hypocotyls (endodermis cells) has been analyzed and compared in order to testify cytoskeleton involvement in the displacement of statoliths in cress (Lepidium sativum L.) seedling statocytes. After 32 h of growth at 1 g or under a fast clinorotation (50 rpm), the seedlings were treated for 24 min as follows: exposition to clinorotation or 180° inversion and the action of gravitational force in root tip or hypocotyl tip direction. Statolith displacement was studied by light microscopy on semi-thin longitudinal sections of hypocotyls and root caps, measuring the distance between the centre of plastids and morphological cell bottom. Considerable temporal differences have been determined between the kinetics of the longitudinal motion of amyloplasts in root and hypocotyl statocytes of 1-g seedlings upon exposition to fast clinorotation and inversion. In statocytes of both organs of seedlings grown under fast clinorotation, the gravity provoked displacement of statoliths in the direction of its action; however, the displacement was much faster in hypocotyl than in root statocytes. It has been assumed that the gravity-determined longitudinal transport of amyloplasts, both in hypocotyl endodermic cells and root statocytes of cress seedlings, is modulated by the cytoskeleton.