CHARACTERISTICS AND IMPLICATIONS OF PROLONGED FUSICOCCIN-INDUCED GROWTH OF AVENA-COLEOPTILE SECTIONS

A study has been made of the prolonged growth of Avena coleoptile sect ions in response to fusicoccin (FC), a phytotoxin that promotes apopla stic acidification. The final amount of FC-induced growth is a functio n of the FC concentration. Removal of the epidermis speeds up the init ial rate of elongation and shortens the duration of the response, with out affecting the total amount of extension. A suboptimal FC concentra tion (7x10(-8) M) which induces the same rate of proton excretion as d oes optimal indoleacetic acid (IAA) (1x10(-5) M), causes elongation wh ich is 60-75% of that induced by IAA in 4 h or 50-65% in 7 h. This sug gests that acid-induced extension could make a major contribution to a uxin-induced growth for at least 7 h.