Secondary metabolism and antioxidants
are involved in environmental adaptation
and stress tolerance in lettuce
Lettuce (Lactuca sativa) plants grown in a protective environment, similar to in vitro
conditions, were acclimated in a growth chamber and subjected to water stress to
examine the activation of genes involved in secondary metabolism and biosynthesis
of antioxidants. The expression of phenylalanine ammonia-lyase (PAL), g-tocopherol
methyl transferase (g-TMT) and L-galactose dehydrogenase (L-GalDH) genes involved
in the biosynthesis of phenolic compounds, a-tocopherol and ascorbic acid,
respectively, were determined during plant adaptation. These genes were activated
in tender plants, grown under protective conditions, when exposed to normal
growing conditions in a growth chamber. A large increase in transcript level for PAL,
a key gene in the phenylpropanoid pathway leading to the biosynthesis of a wide
array of phenolics and flavonoids, was observed within 1 h of exposure of tender
plants to normal growing conditions. 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.
Published by Elsevier GmbH.