Inhibition of root elongation in microgravity by an applied electric field

Roots grown in an applied electric field demonstrate a bidirectional curvat ure. To further understand the nature of this response and its implications for the regulation of differential growth, we applied an electric field to roots growing in microgravity. We found that growth rates of roots in micr ogravity were higher than growth rates of ground controls. Immediately upon application of the electric field, root elongation was inhibited. We inter pret this result as an indication that, in the absence of a gravity stimulu s, the sensitivity of the root to an applied electric stimulus is increased . Further space experiments are required to determine the extent to which t his sensitivity is shifted. The implications of this result are discussed i n relation to gravitropic signaling and the regulation of differential cell elongation in the root.