Abstract
Avena coleoptiles excrete hydrogen ions in response to the hormone auxin. Both auxin-induced cell elongation and hydrogen ion excretion occur after only a short lag, and both are prevented by either carbonyl cyanide m-chlorophenylhydrazone or cycloheximide. These results support the idea that hydrogen ions act as a second messenger in auxin-induced cell elongation and can be the wall-loosening factor.