Abstract
Adverse environmental conditions cause oxidative stress in plants
by generation of ¿reactive oxygen species¿ (ROS), to which plants
respond activating enzymatic and non-enzymatic antioxidant systems.
Many phenolic compounds, especially flavonoids, are known
antioxidants and efficient ROS scavengers in vitro; this activity
appears to be the reason for their attributed beneficial effects for
human health. There are evidences for the involvement of phenolics/
flavonoids in plant responses to abiotic stress, mostly based on
experiments with model species under controlled (but artificial)
greenhouse conditions; yet their role in stress tolerance mechanisms
in nature is still unclear. There are large quantitative and
qualitative differences in antioxidant phenolics in plant taxa, which
makes it difficult to generalise the results obtained for particular
species. Moreover, phenolics fulfil many different biological functions
in plants, which can mask their specific effects on the defense
against environmental stress.
Our strategy to assess the biological relevance of these secondary
metabolites in abiotic stress tolerance mechanisms is based
on the correlation between the levels of total phenolics and antioxidant
flavonoids and the degree and type of stress, in plant material
collected in the field from a relatively large number of plant species
growing under varied environmental conditions (different habitats,
several seasons throughout the year). Despite the aforementioned
difficulties, we could detect statistically significant correlations of
phenolics contents with altitude and with soil and atmospheric
parameters associated to water stress, thus supporting a general,
ecologically relevant function of antioxidant phenolic compounds
in the mechanisms of response to environmental stress in plants.
