Quantification of endogenous IAA and lAAsp was carried out during adventitious root formation in avocado microcuttings. Both auxin and conjugate were monitored in control cuttings (rooted in the absence of auxin) as well as in cuttings treated with a rooting promotor (IBA) or an auxin transport inhibitor (TIBA). Additionally, a histological study to follow root differentiation was carried out. In control cuttings IAA levels remained constant throughout the rooting process, however, in IB A-treated cuttings IAA levels increased 2-fold during the first 6 d. Addition of 200 μM TIBA induced a slight decrease of IAA levels and inhibited root formation. As for IAAsp levels, both control and IBA-treated cuttings showed a big increase before root differentiation occurred and as the process went on, a progressive decrease took place. However, in TIBA-treated cuttings IAAsp levels not only did not increase but diminished progressively during the process. The role of auxin conjugates during the rooting process of avocado is discussed.
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García-Gómez et al. (1994) studied this question.