Exogenous phenylalanine application effects on phytochemicals, antioxidant activity, HPLC profiling, and PAL and CHS genes expression in table grapes (Vitis vinifera cv. 'Qzl Ouzum').

BACKGROUND: Grape (Vitis vinifera L.) is one of the most important fruit products globally and has a high nutritional value with potent antioxidant and anti-cancer activities. In current years, phenylalanine application has been particularly noticed for enhancing the nutritional quality of horticultural crops. With the aim of quality improvement, the effects of foliar application of phenylalanine at 5 concentrations (0, 100, 500, 1000, and 2000 μM) on Vitis vinifera cv. 'Qzl Ouzum' berry compositions were studied. The studied parameters included antioxidant activity, phenolics, flavonoids, anthocyanin, catalase and phenylalanine ammonia-lyase enzyme activity, and phenolic compounds content based on HPLC analyses (myricetin, quercetin, kaempferol, syringetin, catechin, gallic acid, caffeic acid, p-coumaric acid, resveratrol). RESULTS: Phenylalanine at 1000 μM increased total phenols, flavonoids, anthocyanins, and PAL enzyme activity. In addition, HPLC analysis revealed a significant accumulation of individual phenolic compounds by phenylalanine treatment. The highest values were recorded in the treatments with 100 and 500 μM phenylalanine for most of the phenolic components. Real-time quantitative RT-PCR results showed that the expression of PAL and CHS genes was induced by phenylalanine. The highest PAL and CHS gene expression was observed at 500 μM and then at 1000 μM phenylalanine treatment. CONCLUSIONS: With the use of phenylalanine, the activity of the PAL and CHS enzyme and PAL and CHS gene expression were significantly increased and led to a greater accumulation of phenolic compounds and antioxidant activiety. This study suggests that the use of phenylalanine as a main precursor for the synthesis of phenolic compounds, can improve the phenolic composition of grapes and could be a practical approach to advance fruit quality in the production of grape cv. 'Qzl Ouzum'.