Morphology and Hormone Levels of Tobacco and Carrot Tissues Transformed by <italic>Agrobacterium tumefaciens</italic> III. Formation of IAA Conjugates in Cultured Carrot Tissues Transformed with Wild-type and Mutant Ti Plasmids

Abstract

Inactivation of IAA was examined in cultured carrot tissues transformed with Agrobacterium tumefaciens that harbored wild-type, aux− or cyt− Ti plasmids. IAA oxidase activities were similar among the three types of transformed tissue. Metabolites of IAA were examined by following the fate of 3-indolyl-[l-l4C]IAA. IAA conjugates were detected in all transformed tissues as well as in hypocotyl segments of non-transformed carrot seedlings. The rate of formation of IAA conjugates was ten times higher in the tissues transformed with wild-type or cyt− Ti plasmids than in the tissues transformed with aux− Ti plasmids. When the tissues transformed with aux− Ti plasmids were cultured on medium that contained IAA for 6 h, the rate of formation of IAA conjugates in these tissues became as high as that in tissues transformed with wild-type or cyt− Ti plasmids. The tissues transformed with wild-type or cyt− Ti plasmids not only synthesize larger amounts of IAA but also convert a larger amount of free IAA to conjugated IAA than do non-transformed and aux− transformed tissues. Presumably, in carrot, the formation of IAA conjugates decreases the amount of free IAA in the transformed tissues that synthesize large amounts of IAA and, consequently, the level of free IAA can be maintained fairly constant.