Plant growth, especially the roots, was
retarded in tender plants when exposed to normal growing conditions. Furthermore,
exposure of both protected and unprotected plants to water stress resulted in the
activation of PAL. PAL inhibition by 2-aminoindan-2-phosphonic acid (AIP) rendered
these plants more sensitive to chilling and heat shock treatments. These results
suggest that activation of secondary metabolism as well as the antioxidative
metabolism is an integral part of plant adaptation to normal growing conditions in
lettuce plants.