Abstract:

The purpose of this study was to find out the effect of 5-aminolevulinic acid (ALA) application on phenolic
substances and phenylalanine ammonia lyase (PAL) activity and PAL gene expression in young apple fruits. Apple fruits
were treated with various concentrations of ALA before thinning, and then over a subsequent period of 12 days, total
phenolic contents and PAL activity were measured by UV spectrophotometry and the expression of PAL gene by fluorescent
quantitative real-time polymerase chain reaction (RT-qPCR). The experiment results indicated that as the ALA concentration
increased up to 300 mg/L, the PAL activity, total phenolic content and PAL gene expression levels all showed an increasing
trend, while the opposite pattern was observed for these three parameters when the ALA concentration was further raised
to 400 mg/L. At identical ALA concentrations, all these parameters became significantly higher with prolonged treatment
time, reaching the maximum levels on the 9th day, and began to fall on the 12th day. Thus, it can be concluded that treatment
of young apple fruits with ALA at concentrations around 300 mg/L may result in a variety of desired physiological changes,
such as markedly increasing phenolic substances and improving the activity level and gene expression of PAL.

Key words: young apple fruits, polyphenols, phenylalanine ammonia lyase, gene expression