Dynamics of Actin Filaments in Epidermal Cells of Azuki Bean Epicotyls under Hypergravity Conditions

Abstract

The effects of hypergravity on growth and dynamics of actin filaments were examined in azuki bean (Vigna angularis) epicotyls. Elongation growth occurred mainly in the apical region of epicotyls, which was inhibited by hypergravity at 300 G. The density of actin filaments in epidermal cells decreased from the apical to the basal regions of epicotyls, irrespective of the gravitational conditions, and in the apical region of epicotyls, hypergravity decreased the density. Actin filaments were arranged with longitudinal or radial direction in the epidermal cells of apical region of 1 G-grown epicotyls. On the other hand, actin filaments with transverse direction were observed in basal region of epicotyls grown at 1 G. Similar changes in the arrangement of actin filaments toward the basal region were observed even under hypergravity conditions. Hypergravity had no effects on the growth and reorientation of cortical microtubules, when actin filaments were disrupted by cytochalasin D treatment. These results suggest that modification of dynamics of actin filaments is responsible for reorientation of cortical microtubules, which leads to inhibition of elongation growth in azuki bean epicotyls under hypergravity conditions.