In response to water stress, tender plants did not do as well as unprotected plants. Unprotected plants were better able to adapt to water stress than the tender plants. Adaptation to the stress was associated with the activation of PAL, g-TMT and L-GalDH. It is important to note that this response was somewhat similar to that when tender plants were exposed to the unprotectivecondi- tions. This suggests that plants respond as an adaptive mechanism by activating genes involved in the biosynthesis of antioxidants whenever there is an environmental perturbation. This may explain why even under normal unprotective conditions activation of secondary metabolism genes is im- portant for successful plant growth. A number of studies have shown that genes involved in the phenylpropanoid pathway, including PAL, and those involved in the biosynthesis of tocopherols in a number of plant species are activated in responses to abiotic stresses, including water stress Accumulation of antioxidants such as phenolics, tocopherols and ascorbic acid in re- sponse to a wide range of abiotic stresses and, hence, their importance in plant adaptation has also been recognized Furthermore, studies showing that mutants deficient in secondary meta- bolites or plants with blocked PAL activity are sensitive to environmental stresses clearly demon- strate the role of these antioxidants in plant adaptation Our results, in addition to confirming these findings, suggested a possible role of secondary metabolism in the adaptation to environmental perturbations that occur under normal growing conditions in lettuce plants.