Influence of maturity and bagging on the relationship between anthocyanin accumulation and phenylalanine ammonia-lyase (PAL) activity in 'Jonathan' apples

The influence of maturing and ripening on phenylalanine ammonia-lyase (PAL) activity and anthocyanin accumulation was examined using bagged, non-bagged and shaded 'Jonathan' (Malus domestica) apples. Bagged fruit were covered with paper bags from mid-dune at an early stage of fruit growth. Shaded apples were insulated from sunlight by newspaper at the beginning of colouring (middle September). The apples were harvested at different maturity stages and were irradiated with UV + white light for 96 h at 15 degrees C after which anthocyanin content and PAL activity were measured. In non-bagged and shaded apples, anthocyanin accumulation and maximal PAL activity increased as the apples developed from the immature to the initial ripe stage, then decreased at full ripe stage. A positive linear relationship between the maximum PAL activity and the amount of anthocyanin accumulated suggested that the change in PAL activity is involved in the change of anthocyanin accumulation. In the bagged apples in the immature stage, anthocyanin accumulation and peak PAL activity after irradiation was higher than that in non-bagged apples. However, as the apples ripened, anthocyanin accumulation was less than for less mature fruit, even though PAL activity was relatively high. Therefore, PAL is not the only regulating factor for anthocyanin accumulation in bagged mature and ripe fruit. (C) 2000 Elsevier Science B.V. All rights reserved.