Ethylene as a natural agent inducing plumular hook formation in pea seedlings.

Removing endogenous ethylene by hypobaric treatment, or displacing it with carbon dioxide inhibits hook development in etiolated pea seedlings. When seedlings are returned to a normal atmosphere, hook formation occurs in darkness. Addition of ethylene accelerates this process. When ethylene induces hook formation, cell division in the hook tissue is rather inhibited by the gas. These data suggest that endogenous ethylene causes formation of the hook by inducing expansion of certain cells.