Polar transport and content of indole-3-acetic acid in wounded sweet potato root tissues

In roots of sweet potato (Ipomoea batatas Lam. cv. Kokei 14), the metabolic response to wounding was remarkable in the proximal side and developed in the acropetal direction. We assumed that the polarity resulted from the increase in polar movement of indoleacetic acid (IAA) (1977, Plant Physiol. 60: 563–566). Transport of IAA and change of the IAA level in the wounded tissue of sweet potato roots were investigated. Transport of the label from 14C-IAA was obviously polarized in the acropetal direction. 14C-IAA administered to the wounded tissue was mainly metabolized into two conjugates of IAA. The amount of IAA in the wounded tissue, determined by the spectrofluorometric method, increased about 3-fold after 18 hr of incubation prior to the development of activities of some enzymes. The increase in IAA content was not affected with aseptic incubation, therefore, the possibility of IAA production by microorganisms on the wounded tissue was excluded. The results obtained strongly support our hypothesis that IAA plays an important role in the metabolic response to wounding.