Evidence that Auxin-induced Growth of Soybean Hypocotyls Involves Proton Excretion

The role of H(+) excretion in auxin-induced growth of soybean hypocotyl tissues has been investigated, using tissues whose cuticle was rendered permeable to protons or buffers by scarification (scrubbing). Indoleacetic acid induces both elongation and H(+) excretion after a lag of 10 to 12 minutes. Cycloheximide inhibits growth and causes the tissues to remove protons from the medium. Neutral buffers (pH 7.0) inhibit auxin-induced growth of scrubbed but not intact sections; the inhibition increases as the buffer strength is increased. Both live and frozen-thawed sections, in the absence of auxin, extend in response to exogenously supplied protons. Fusicoccin induces both elongation and H(+) excretion at rates greater than does auxin. These results indicate that H(+) excretion is involved in the initiation of auxin-induced elongation in soybean hypocotyl tissue.