Effects of 2,3,5-triiodobenzoic acid (TIBA) on stem growth induced by indole-3-acetic acid (IAA) and naphthylacetic acid (NAA) in precooled rooted tulip bulbs

Effects of 2, 3, 5-triiodobenzoic acid (TIBA) on stem growth induced by indole-3-acetic acid (IAA) and naphthylacetic acid (NAA) in precooled rooted tulip bulbs were studied. TIBA is effective in inhibiting either IAA- or NAA-induced elongation either below or above the point of treatment. Time lag of the treatments between IAA and TIBA did not give significant differences in the length of any internode. When IAA was applied additionally on the middle of the ard internode, it restored the growth inhibition of the 1st to 3rd internodes caused by TIBA applied on the 4th internode, but the restored growth did not reach to the length promoted by IAA only. The difference in the total internode length between the treatments with 0.1% IAA and 0.1% IAA+TIBA on the middle of the 4th internode was much smaller than that between the treatments with 2.0% IAA and 2.0% IAA + TIBA. Presented results using TIBA, an inhibitor of basipetal transport of auxin, confirmed crucial role of auxin in tulip stem growth.