Characterization of Antioxidant Responses in Plants of Ipomoea Nil Cv. Scarlet

It is well known that antioxidants of the ascorbate glutathione cycle play an important role on this defensive process of plants growing in the abiotic conditions, during both normal metabolic activities, as the photoreduction of the O2 into the thylakoids (Chernikova et al., 2000) and by exogenous reasons, as the entrance of ozone to the plant (Iriti & Faoro 2008). Ascorbic acid (AA) is one of the most important antioxidants in plants. Hydrogen peroxide (H2O2) is decomposed while this antioxidant is oxidized to dehydroascorbic acid, a reaction that is mediated by ascorbate peroxidase. AA is also considered an important molecule against ozone due to its occurrence in cellular walls and membranes, once this pollutant enters the plant predominantly through the stomata and reacts immediately with water in the apoplast intensifying the ROS formation. The seasonality in the contents of leaf AA also affects ozone sensitivity of some plant species (Ferreira et al., 2007). As scavenger of radical superoxide, the enzyme superoxide dismutase (SOD) is other important tool to defend plants against oxidative stress (Esposito et al., 2009). Such antioxidants may have seasonality in their formation and activity due to exogenous factors, as for example, meteorological conditions, even in the absence of anthropic interference. This is a consequence of the fact that the seasonality in solar radiation, photoperiod, temperature and relative humidity, for example, beyond influencing the stomata aperture, regulates the processes of photosynthesis and respiration on chloroplasts and mitochondria and thus the natural production of ROS in the cells (Takac, 2004, Foyer & Noctor 2005). During the aging of the plant, variations in the levels of antioxidants may also occur (Iriti et al., 2009). Therefore, it is hypothesized that variations in antioxidant responses throughout the life cycle occurs, taking the plant more susceptible to diverse environmental factors of stress, and that the seasonality in the climatic conditions can intervene with such variations, becoming the plant more or less vulnerable throughout the seasons of the year during their growth at the natural environment. In thesis, these hypotheses are also valid to the cultivar Scarlet O’Hara of Ipomoea nil, object of the present study. Besides its potential as an ornamental flowering climbing plant, it is sensitive to ozone and is indicated for biomonitoring of air quality (Nouchi & Aoki 1979). Therefore, the range of antioxidant responses to naturally varying meteorological conditions should be known before its usual application as ornamental or bioindicator plant in a determined environment.