# Metabolism and Regulation of Ascorbic Acid in Fruits
## 5 Effects of Hormones on the Ascorbic Acid Accumulation in Fruits  
Classical plant hormones mainly include auxin, cytokinin, gibberellin (GA), ethylene, abscisic acid (ABA), salicylic acid (SA), jasmonic acid (JA), and brassinolide, which play an important regulatory role in fruit ripening and nutritional quality. Many studies have used phytohormones to regulate the accumulation of AsA in fruits. Application of GA3 to plum fruit delays the decrease in AsA concentration and reduces flesh browning development during storage at low temperature [118]. The combined treatments of GA3 and phenylurea significantly delay the losses in AsA contents and suppress fruit softening of harvested banana fruit [119]. GA3 (50 ppm) + 1-methyl-cyclopropane-treated strawberry fruits increase the retention of vitamin C over their shelf life compared to the control group [120]. Exogenous gibberellin and ethylene treatments can also significantly increase ascorbic acid content in citrus fruits [121]. According to a recent study, 6-benzylaminopurine and kinetin increase the AsA content of strawberry fruits by 33.96% and 27.22%, respectively, compared to the control [122]. The plant growth regulator ABA plays a role in fruit ripening. Abscisic acid and ethylene regulate AsA synthesis through antagonism [123]. It has been found that ABA alters the AsA redox state at the early stages of fruit development and more than doubles AsA levels at the end of fruit ripening in red raspberry (_Rubus ideas_ L.) [124]. Strawberry had a 1.6-fold increase in ascorbic acid content after treatment with 1 uM abscisic acid [125]. La(NO3)3 treatment can induce ABA synthesis in strawberry fruit [126]. At the same time, La(NO3)3 increases the activities of DHAR, MDHAR, and GalLDH and decreases the activities of APX and AOO, resulting in increased AsA content in strawberry fruit [126]. Tungstate is an ABA synthesis inhibitor. Tungstate treatment can activate the expression of GR, MDHAR, and GalLDH, while inhibiting the expression of DHAR and APX, thereby inhibiting the accumulation of AsA in strawberry fruit [126]. SA is a vital phytohormone involved in regulating plant resistance to various biotic and abiotic stresses. Treatment with 2 mM SA can maintain the level of AsA and reduce the chilling injury of pomergnate fruit during low-temperature storage [127]. SA treatment also significantly delays the reduction in AsA content in plum, cornelian cherry, pineapple, \begin{table}
\begin{tabular}{l l l l l l l} \hline
**Common** & **Gene** & **Gene** & **Target Gene** & **Combination** & **Effect** & **Reference** \\
**Name** & **Name** & **Source** & **Target Gene** & **Combination** & **Effect** & **Reference** \\ \hline kiwifruit & ERP91 & kiwifruit & GGP3 & protein-DNA & Positively regulate the expression of GGP3 and the accumulation of AsA. & [112] \\  & MYBS1 & kiwifruit & GGP3 & protein-DNA & Positively regulate the expression of GGP3 and the accumulation of AsA. & [92] \\  & ESE3 & kiwifruit & GGP3 & protein-protein & Positively regulate the accumulation of AsA & [91] \\  & MYBR & kiwifruit & GGP3 & protein-protein & Positively regulate the accumulation of AsA & [91] \\ \hline \end{tabular}
\end{table} 
Table 3: _Cont._pear, and strawberry fruits during low-temperature storage and improves the resistance of fruits to low-temperature stress [128; 129; 130; 131; 132]. Under the combined treatment of 1.0 mM SA and 2% chitosan, the content of AsA in lychee fruit is maintained at a high level [133]. In addition, using chitosan combined with SA treatment can effectively increase the AsA content of grapefruit fruit and activate the disease resistance to green mold [134]. In addition to SA, JA is also believed to play a variety of essential roles in regulating stress responses and plant growth [135]. MeJA treatment can significantly increase the AsA content in star fruit, blueberry, and pineapple fruits and delay the quality decline of fruits under low-temperature storage [136; 137; 138].