*3.4. Changes in Endogenous Hormone Content and Ratio during the Rooting Process of Vegetable Mulberry Cuttings*

#### 3.4.1. Changes in Endogenous IAA Content

Both the control and treatment groups exhibited a trend of first decreasing before increasing in IAA content (Figure 3A). The IAA contents of the treatment groups and the control group presented a decreasing trend during the callus formation period, possibly due to increased peroxidase activity in the cuttings after separation from the mother plant, resulting in a decrease of IAA content. During this period, callus formation occurred at the lower end of the cutting, which consumed IAA and also reduced IAA content. Simultaneously, compared with the control group, the decrease in IAA content of ABT-1—treated groups was smaller, probably because of the reversal of exogenous hormone absorption by the cuttings themselves after ABT-1 treatment. In general, the IAA content of ABT-1—1000 mg·L−<sup>1</sup> was consistently higher than that of other treatments during each time period, suggesting that root growth can be promoted by high levels of IAA.

#### 3.4.2. Changes in Endogenous ABA Content

As indicated in Figure 3B, ABA content exhibited a trend of initial increase followed by a decrease. During the initiation period, the treatment groups and the control group showed an upward trend, possibly due to the increase in ABA secretion from the cuttings in response to external stimuli for separation from the mother plant. The ABA content reached a peak during the callus formation period, followed by a decrease. In this process, the root primordia gradually developed and began to produce adventitious roots. By this time, the ABA content of ABT-1—1000 mg·L−<sup>1</sup> decreased sharply, even lower than that during the initiation period, while the ABA content of the control group remained relatively high, indicating that a low level of ABA content is beneficial to the production and elongation of adventitious roots.

**Figure 3.** Effect of ABT-1 treatment on endogenous hormone content during the rooting process of vegetable mulberry cuttings. (**A**–**I**) represents the changes in endogenous hormone contents of IAA, ABA, ZR, GA3, JA, SL, IBA, IAA/ABA, and IAA/ZR in the treatment and control groups of vegetable mulberry under the action of ABT-1 during the rooting period. Different lowercase letters indicate notable differences among the treatments (LSD multiple comparison analysis, *p* < 0.05). A1 represents 200 mg·L−<sup>1</sup> ABT-1 treatment group, A2—denotes 500 mg·L−<sup>1</sup> ABT-1 treatment group, A3—signifies 1000 mg·L−<sup>1</sup> ABT-1 treatment group and CK1—indicates the control group. Stage 1 represents the initiation stage, Stage 2—refers to the callus formation stage and Stage 3—denotes the adventitious root formation and elongation stage.

## 3.4.3. Changes in Endogenous ZR

The trend of ZR content showed an initial decrease followed by an increase (Figure 3C). During the initiation period, the ZR content of the control group was higher than that of the treatment groups, suggesting that ABT-1 reduces the ZR content in cuttings. During the callus formation period, the ZR content of the control group exhibited a sharp decrease, while the treatment group only presented a slight decrease, indicating that some ZR is consumed by the formation of callus tissue in cuttings. Meanwhile, the control group demonstrated a poor ability to synthesize ZR, so ZR content exhibited a rapid decrease. During the adventitious root formation and elongation period, ZR content presented varying degrees of increase in both the treatment and control groups, thus promoting cell division and growth and benefiting growth and development of adventitious roots.
