5-ALA is an essential precursor for porphyrin biosynthesis. It promotes soluble sugar accumulation in fruit and improves both appearance and flavour quality. Studies show that after treatment with 100 mg/L 5-ALA, fig peel redness (a*) reached 28.10, total anthocyanin in the peel peaked at 473.75 nmol/g, and total soluble solids in ripe fruit reached 17.6% (1.1 times the CK group) — ultimately delivering earlier and more uniform colour development and higher sugar levels, and significantly improving commercial quality.
Effect of 5-ALA treatment on fruit external colouring
Exogenous 5-ALA significantly promoted colouring in ‘Bojihong’ figs and increased the redness parameter (a*) of both peel and flesh (a* represents fruit redness). From 10 d onwards, the peel and flesh (a*) of the 5-ALA-treated group were significantly higher than those of the control group; at 30 d the peel (a*) reached a peak of 28.10. It was observed that 5-ALA-treated fruit turned red earlier and coloured more uniformly, and 100 mg/L gave the best overall colouring and sugar quality.
Effect of 5-ALA on internal fruit quality (total soluble solids and soluble sugars)
5-ALA increased the content of total soluble solids (TSS), total soluble sugars, and the individual sugar components glucose, fructose and sucrose in the fruit.
In fruit treated with 5-ALA, total soluble solids reached 17.6%, 1.1 times that of the control group. In both peel and flesh, glucose accounted for the highest proportion of the soluble sugars, followed by fructose and sucrose.
After 30 d of 5-ALA treatment, the peel contained 36.85 mg/g glucose, 26.08 mg/g fructose and 4.25 mg/g sucrose; the flesh contained 47.76 mg/g glucose, 33.85 mg/g fructose and 5.74 mg/g sucrose.
Correlation analysis showed that fructose, glucose, sucrose and total soluble sugar contents were very significantly positively correlated with anthocyanin accumulation — sugar accumulation promotes anthocyanin synthesis.
Effects of 5-ALA on pigments (anthocyanin, chlorophyll and carotenoids)
Accelerates chlorophyll degradation and promotes anthocyanin and carotenoid accumulation
Total anthocyanin: after 30 d of 5-ALA treatment, peel anthocyanin reached a peak of 473.75 nmol/g; flesh anthocyanin peaked at 155.44 nmol/g at 25 d. Peel anthocyanin content was overall higher than that of the flesh.
Chlorophyll: 5-ALA accelerated chlorophyll degradation in both peel and flesh; peel chlorophyll fell sharply at 15 d after treatment and flesh chlorophyll at 10 d.
Carotenoids: after 30 d of 5-ALA treatment, peel carotenoids increased by 6.31 µg/g and flesh carotenoids by 3.09 µg/g compared with the control.
Individual anthocyanin components: the main anthocyanins in ‘Bojihong’ fig are cyanidin-3-rutinoside (C3R) and cyanidin-3-glucoside (C3G). 5-ALA treatment promoted substantial accumulation of both.
After 30 d of treatment, peel C3R peaked at 161.48 µg/g and flesh C3R at 47.78 µg/g; peel C3G was 1.78 times that of the control group. C3R began to accumulate 10 d after treatment, and C3G 15 d after treatment.
5-ALA regulates the activity of key enzymes in anthocyanin synthesis (physiological mechanism)
5-ALA increased the activities of the key enzymes PAL, CHI, DFR and UFGT in the anthocyanin synthesis pathway, with a stronger effect in the peel than in the flesh.
After 5-ALA treatment, in fig fruit:
By increasing the activity of key enzymes in the phenylpropanoid–flavonoid pathway, 5-ALA drives a stronger metabolic flux towards anthocyanin biosynthesis.
5-ALA regulates the expression of genes related to anthocyanin synthesis (molecular mechanism)
Expression timing of structural genes: FcPAL, FcCHS and FcDFR mostly peaked at 20 d after treatment and then declined; FcCHI and FcUFGT continued to be up-regulated later, peaking at 30 d.
Regulatory genes: FcMYB123 rose first and then declined; in the peel its expression at 20 d was 2.1 times the control, and in the flesh its expression at 25 d was 4.9 times the control. FcWD40 was significantly higher than the control in most periods.
Exogenous 5-ALA induces the expression of genes related to the MYB–WD40 transcriptional regulatory complex, which further activates the full set of downstream anthocyanin biosynthesis structural genes, raising the activity of the corresponding synthase proteins and ultimately promoting the synthesis and accumulation of anthocyanin monomers. At the same time it accelerates chlorophyll degradation, and together these improve fruit colouring. In addition, 5-ALA promotes sugar accumulation, and sugars act both as precursors and as signalling substances that further synergistically promote anthocyanin production, forming a positive sugar–anthocyanin synergistic effect.
Conclusion
Pre-harvest spraying of 5-ALA on the fruit is an effective means of improving fruit appearance and quality. This study shows that 5-ALA treatment significantly increased the (a*) value and anthocyanin content of ripe figs, reduced chlorophyll content, promoted the accumulation of soluble sugars and their components, enhanced the activity of enzymes related to anthocyanin synthesis, and activated the structural and regulatory genes of the anthocyanin biosynthesis pathway.
Therefore, a 100 mg/L 5-ALA treatment in production can improve fig fruit quality. It should be noted that this trial applied pre-harvest 5-ALA spraying to ‘Bojihong’ fig only; in practical production, the characteristics of different fig cultivars and environmental factors must be fully considered in order to obtain the best results and economic benefits.
Source: Exogenous 5-aminolevulinic acid enhances the quality and anthocyanin synthesis ability of fig fruit, Horticulture, Environment, and Biotechnology, 2025, 66:1223–1235.