Effects of gibberellic acid (GA3) on strawberry PAL (phenylalanine ammonia-lyase) and TAL (tyrosine ammonia-lyase) enzyme activities

Gibberellic acid (GA(3)) treatments (30 and 60 mu g litre(-1)) were applied to young plants (Fragaria ananassa cv Chandler). Fruits were harvested at various developmental stages (14, 21, 28 and 35 days from fruit set). Weight and size, phenolic compounds (total polyphenols and anthocyanins) and enzyme activities, phenylalanine ammonia-lyase (PAL) and tyrosine ammonia-lyase (TAL) were determined. Our aim was to obtain detailed information about PAL and TAL activities related to the strawberry colour during development and ripening processes and to determine the effects of exogenous treatments of GA(3) on PAL and TAL activities. Exogenous treatments of GA(3) improve weight, size and colour of strawberry fruits, and affect PAL and TAL activities. We found that the anthocyanin content and PAL activity are enhanced by the exogenous treatment of GA(3) in the range of 30 mu g litre(-1). However, with the higher GA(3) treatment, only the anthocyanin content is affected in that way. These findings suggest that gibberellic acid effect on PAL, TAL and ultimately anthocyanin enhancement is dosage related and saturation of the response occurs at 30 mu g litre(-1). (C) 1998 SCI.