IN VITRO RESPONSE OF MELISSA OFFICINALIS TO OXIDATIVE STRESS IMPOSED BY OZONE

Tropospheric O3 is an important air pollutant that causes negative effects on photosynthetic machinery and other crucial processes in plants. A multitude of ROS-generating systems during the O3-induced oxidative burst have been reported; however plants display efficient enzymatic and non-enzymatic antioxidant systems. Gas exposure of in vitro culture is an easy, cost-effective way of treating plants to air pollutants for experimental purposes. The present work focuses on testing the ability of in vitro Melissa officinalis to respond to O3 stress (200 ppb, 3 h). No foliar symptoms are observed in fumigated plants. Nevertheless membrane integrity and fast kinetics of chl a fluorescence are significantly affected by O3 (+17% of TBARS levels and -25% of Fv/Fm, respectively). An overproduction of O2- and H2O2 (+31% and +64%, respectively) is also assessed. PAL, CAD and SKDH activity significantly increases (+74, +54 and +90%) twinned to a pronounced increase of total phenols, lignins and tannins (+45, +46 and +82%). In particular a 3-fold raise of rosmarinic acid concentration is detected. Physiological and pharmacological implications of these findings are worthy of further attention.