3.5.2. Changes in Endogenous ABA

The ABA content presented a trend of first increasing and then decreasing (Figure 4B). During the initiation period, the ABA content in the treatment groups was higher than that in the control group, and the ABA content in both the treatment and control groups exhibited an increasing trend, with a peak reached during callus formation. This may be caused by the stress response of cuttings to the environment after detachment from the mother plant, resulting in an increase in ABA content and accumulation of nutrients, which is conducive to callus formation and survival of cuttings. After callus formation, the ABA content began to decrease. During the adventitious root formation and elongation period, ABT-1—500 mg·L−<sup>1</sup> had the lowest ABA content, namely 22.3 ng·g<sup>−</sup>1, merely 49% of that of the control group (45.4 ng·g<sup>−</sup>1), suggesting that high ABA concentration inhibits adventitious root formation and elongation.
