EFFECT OF 2,3,5-TRIIODOBENZOIC ACID ON CAULOGENESIS IN CALLUS-CULTURES OF TOMATO AND PELARGONIUM

Stem explants from winter grown tomatoes cultured on a cytokinin, auxin‐free medium, developed one or two adventitious shoots at the top end of the explant. Addition of the auxin transport inhibitor. 2,3,5‐triiodobenzoic acid (TIBA) to the medium stimulated caulogenesis with loss of polarity. Callus, initiation in pelargonium and ‘geranium’ petiole explants requires both auxin and cytokinin. On transfer, after callus induction to an auxin‐free medium, rhizogenesis occurs in pelargonium cultures followed by caulogenesis. Few shoots develop and unless these are removed, further caulogenesis is suppressed. Bud‐like structures were formed in the callus. Subculture on auxin‐free medium containing cytokinin and TIBA resulted in shoot formation from these bud‐like organs. An analogy with apical dominance is suggested. In ‘geranium’ callus, shoots developed with a low frequency (c. in 2% of the cultures): caulogenesis was increased to 80% when calli were subcultured from auxin‐free, cytokinin medium after green nodule formation to cytokinin‐TIBA medium. Histological studies of green nodules in ‘geranium’ callus indicated a variation in morphological development within and between nodules. It is suggested that auxin synthesis may occur at some microscopic stage in morphogenesis in ‘geranium’ cultures which suppresses further caulogenesis. This may be overcome by the addition of TIBA to the medium at the appropriate stage in morphogenesis. The possible interaction of endogenous auxin in morphogenesis is discussed. Copyright © 1979, Wiley Blackwell. All rights reserved