Gerbera jamesonii is a popular cut flower, yet its postharvest quality is often compromised by neck bending (NB) and short vase life. This study evaluated the effects of phenylalanine (Phe) at concentrations of 0, 10, 20, 40, and 80 mg L−1 on the postharvest performance of ‘Ravel’ gerbera flowers during storage at 21 °C and 65–70% relative humidity over seven days. The results showed that Phe at 40 mg L−1 was the most effective treatment, significantly (p < 0.05) reducing NB severity by 81.7% and increasing vase life by 42.9% compared to the control (10 vs. 7 days). This concentration also enhanced vase solution uptake (4.3 vs. 2.66 mL) and maintained membrane integrity, as indicated by lower electrolyte leakage (36.3% vs. 62.8%). Phe treatment significantly reduced levels of hydrogen peroxide, malondialdehyde, and proline, while preserving higher total protein content (0.69 vs. 0.43 g kg−1). It also enhanced antioxidant enzyme activities, including catalase, peroxidase, and superoxide dismutase. Furthermore, Phe-treated flowers retained higher total phenol and flavonoid levels, increased Pheammonia-lyase activity, and exhibited reduced polyphenol oxidase activity. Lignin content in stems was significantly higher in treated flowers (353.23 vs. 240.86 mg kg−1), accompanied by elevated activity of key lignin biosynthesis enzymes cinnamyl alcohol dehydrogenase and cinnamoyl-CoA reductase. In conclusion, Phe at 40 mg L−1 effectively enhances the postharvest quality of cut gerbera by reducing oxidative stress, strengthening antioxidant defense, and promoting lignin biosynthesis. These findings offer a practical approach to extend vase life and minimize structural failure in commercial floriculture.
