Effects of hydrogen peroxide on initial growth and enzymatic antioxidant system of lactuca sativa l (asteraceae)

Reactive oxygen species (ROS), such as hydrogen peroxide (H/sub 2/O/sub 2/), can function as signaling molecules in basic cellular processes in plants, or cause oxidative damage to biomolecules when in excess. The objective of this study was to evaluate H/sub 2/O/sub 2/phytotoxicity on germination, growth, initial development and cell cycle, in addition to the response of the enzymatic antioxidant system of L. sativa. For this purpose, L. sativa seeds were exposed to H/sub 2/O/sub 2/ solutions at the following concentrations: 0.0, 1.0, 2.5, 5.0, 7.5 and 10 mM for a period of 7 days. After 24 hours of exposure to H/sub 2/O/sub 2/, there was a significant reduction in germination percentage from 2.5 mM. With the increase in H/sub 2/O/sub 2/ concentration, there was a reduction in root length, and seedling fresh and dry biomass. However, dry biomass was more affected by H/sub 2/O/sub 2/ when compared to fresh biomass. H/sub 2/O/sub 2/ significantly reduced mitotic index, but did not induce significant chromosomal abnormalities. The treatment with 7.5 mM H/sub 2/O/sub 2/ led to a significant proline accumulation. On the other hand, the activity of superoxide dismutase and ascorbate peroxidase increased significantly only at a concentration of 2.5 and above 5.0 mM, respectively. There was no significant activity of the enzymes catalase and guaiacol peroxidase. Therefore, the exposure to H/sub 2/O/sub 2/ resulted in proline accumulation, and an increase in antioxidant enzyme activity, in response to H/sub 2/O/sub 2/ increase to maintain redox homeostasis inside the cell. (author)