## 4 Discussion  
### The Relationship between the DCIP and IBMP Accumulation  
In 2020 and 2021, the IBMP content in all treatments showed a continuous downward trend during the experiment period, which means the experiment treatments time point was close to the peak IBMP accumulation period in the experimental grape berries. This phenomenon was similar to our previous study about Leu and AMPA effect on IBMP biosynthesis, which was carried out in the same vineyard [35]. What is more important, these results showed that the IBMP accumulated at pre-veraison and degraded after veaison until harvest, which was consistent with the finding of previous studies [36; 37; 26; 38].  
Figure 5: Effect of DCIP treatment on the relative expression levels of VvOMTs in berry skins during the experimental period: (**a**) _VvOMT1_, (**c**) _VvOMT2_, (**e**) _VvOMT3_, and (**g**) _VvOMT4_ in the 2020 season, and (**b**) _VvOMT1_, (**d**) _VvOMT2_, (**f**) _VvOMT3_, and (**h**) _VvOMT4_ in the 2021 season. The symbol * and ** indicate significant differences at \(p\leq 0.05\) and \(p\leq 0.01\) between control and DCIP treatment, respectively.  
Moreover, the IBMP concentration of grapes in all treatments were all below the quantitation limit in the two consecutive years at harvest (154 DAA in 2020, 153 DAA in 2021). These results show that delaying the harvest time is really an effective way to reduce the IBMP content in wine grapes.  
It is noteworthy in this study that, regardless of whether the IBMP content was expressed in nanograms per kilogram or picograms per berry, the incorporation of DCIP in _situ_ significantly increased the IBMP concentration of grape at maturity (121 DAA in 2020, 101 and 118 DAA in 2021) for 2 consecutive years.  
On the one hand, these results suggest that DCIP might participate in the biosynthesis of IBMP in grape berry. The reason why the IBMP concentration only increased at maturity compared with the Control and Mock treatments, it might be because there are series of steps between the DCIP and IBMP, and the DCIP converts into the corresponding key intermediate at a slow rate, so the IBMP concentration of grape berry would not increase immediately and showed significant increase until the later experiment period.  
On the other hand, the IBMP concentration after DCIP treatment showed a significant increase at maturity (i.e., post-veraison) when it is generally believed that IBMP in grape berry is in a degradation stage [36; 37; 38; 39] compared with the Control and Mock treatments at the same sampling time points. It further suggested that IBMP metabolism in grape berry might be a dynamic equilibrium process between the biosynthesis and degradation [35]. In other words, the degradation rate of IBMP in grape berry is faster than the biosynthesis rate after veraison under normal growth condition, so the IBMP content in grape berry showed a continued decline after veraison. Whereas, when the DCIP, which was considered to be the possible key intermediate of IBMP biosynthesis, was incorporated into the grape berry in _situ_, the IBMP biosynthesis process might be accelerated after veraison due to the exogenous DCIP incorporation. Thus, the IBMP content showed a significant increase compared with the Control and Mock treatments at the same time points.  
In view of the results above, the effect of DCIP on IBMP biosynthesis in grapes deserves to be further explored.