Moreover, the increase in the procyanidin content through a water stress effect could also be related with the fact that water deficit can lead to an increase in the levels of free
phenylalanine, a precursor in the procyanidin synthesis, and an increase in L-phenylalanine ammonia lyase (PAL) activity and, probably, PAL synthesis (Castellarin, Matthews, Di Gaspero, &
Gambetta, 2007).