Stimulation of the phenylpropanoid biosynthesis by plant activators in apple leaves

The present work studied the influence of the plant activators Biokal 01, Milsana VP 2001, potassic silicate and SilKaBen on the phenylpropanoid metabolism of apple leaves. Chemical analysis and determination of enzyme activities were carried out in leaves of the scab susceptible apple cv. 'Golden Delicious' and the scab resistant cv. 'Rewena'. The activity of several enzymes of the flavonoid biosynthesis [phenylalanine ammonia lyase (PAL), chalcone synthase/-isomerase (CHS/CHI), flavanone 3-hydroxylase (FHT) and dihydroflavonol 4-reductase (DFR)] was determined. An increasing activity of these enzymes did not stringently cause higher contents of phenylpropanoids. However, changes in the phenylpropanoid content of the apple leaves were related to changes at the enzyme level. Effects of enzyme stimulation could be observed within the first 3 days after application of activating reagents. The phenylpropanoid metabolism was induced faster and stronger in young leaves than adult ones. Changes in the phenylpropanoid metabolism could be found at all times tested within 4 hours to 3 days.