Role of Ethylene in Abscisic Acid-induced Callus Formation in Citrus Bud Cultures

The induction of callus formation in cultured buds of Shamouti orange (Citrus sinensis L.] Osbeck) by abscisic acid (ABA) is a multiphasic process. (Altman, and Goren 1974 Physiol Plant 32: 55.) A study of the mediation by ethylene on this effect of ABA was undertaken. It was found that: (a) ethylene and (2-chloroethyl) phosphonic acid, as well as ABA, induced callus formation; (b) callus induction is best attained when explants are exposed to ethylene during the 1st day after excision; and (c) ABA-induced callus formation is inhibited by rhizobitoxine analog, an inhibitor of ethylene biosynthesis. It is concluded that the effect of ABA on callus formation is mediated via ethylene.