In the present work, 2,3,5-triiodobenzoic acid (TIBA) was applied to uncooled tulip bulbs, cultivars Apeldoorn and Gudoshnik, before flower bud formation, at the beginning of July and after flower bud formation, in October and November. Shoot growth and flowering of partially dry-cooled bulbs were substantially stimulated. These results strongly suggest that TIBA partially replaces the cold requirement of the tulip bulbs. In addition, the effect of TIBA is similar to gibberellins applied exogen- ously to the bulbs. Such a gibberellin application partially substitutes for cold treatment. Gibberellin application stimulates shoot growth and flowering of tulips. The mode of action of TIBA is discussed in relation to auxin action in tulips.
Effects of auxin polar transport inhibitors, 2,3,5-triiodobenzoic acid (TIBA), 1-N-naphthylphthalamic acid (NPA) and methyl 2-chloro-9-hydroxyfluorene-9-carboxylate (morphactin IT 3456), as a lanolin paste, on root formation in cuttings of some species of Crassulaceae, such as Bryophyllum daigremontianum, B. calycinum, Kalanchoe blossfeldiana and K. tubiflora, were studied. Cuttings of these plants were easily rooted in water without any treatment. TIBA and morphactin IT 3456 completely inhibited root formation in the cuttings of these plants but NPA did not when these inhibitors were applied around the stem below the leaves. When TIBA and morphactin were applied around the stem near the top, but leaves were present below the treatment, the root formation was observed in B. calycinum and K. blossfeldiana but in a smaller degree than in control cuttings. These results strongly suggest that endogenous auxin is required for root formation in cuttings of Crassulaceae plants. The differential mode of action of NPA is discussed together with its effect on auxin polar transport.
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