In general, PAL seems to be extraordinary sensitive to the physiological state of the plant.
Levels change as the plant germinates and develops; in mature plants or dormant tissue such
as the potato tuber, it is found only in very low levels, These changes can be the natural ones
occurring during growth, or they may follow wounding, infection drug or y-ray damage,
or activation of phytochrome. It has been noted that there are many examples where there
does not appear to be a direct correlation between the level of PAL and the production of a
specific phenolic compound. This would be the case if, for example, the supply of phenylalanine
were insufficient to saturate the enzyme, or if an enzyme further along a pathway were
draining off the intermediate measured under the experimental conditions.