Ethylene and carbon dioxide: mediation of hypocotyl hook-opening response.

Ethylene at low concentrations inhibits the light-induced opening of the bean hypocotyl hook; auxin inhibits the opening by inducing production of ethylene. Light causes a decrease in ethylene production and an increase in the production of carbon dioxide. Hook opening appears to be a response in which ethylene serves as a natural growth regulator and in which carbon dioxide may be involved also as a growth regulator through its antagonism of the action of ethylene.