THE RESPONSE OF PHASEOLUS-VULGARIS L CV LIT TO DIFFERENT DOSAGES OF THE ANTI-OZONANT ETHYLENEDIUREA (EDU) IN RELATION TO CHRONIC TREATMENT WITH OZONE

A dose-response study with the anti-ozonant ethylenediurea (EDU) and a near-ambient level of ozone (6-h mean of 48 nmol mole(-1) per 6 days each week) was performed in closed chambers on Phaseolus vulgaris L. cv. Lit. Analyses of morpho-functional parameters and biomass measurements were conducted when plants had reached pod maturation (green harvest). The exposure to ozone caused the appearance of extensive symptoms of injury on leaves and their premature abscission; O-3 affected the production of dry matter significantly (52 and 57% reductions in the dry weight of pods and of the total above-ground biomass, respectively), caused a decrease of 50% in the photosynthetic capacity, reduced the chlorophyll a content (36%) and influenced peroxidase activity. All these effects were limited or avoided by the EDU treatment, The efficacy of this protection was directly related to the EDU concentration (varying from 60 to 120 mg per plant), being total at the higher level of the anti-ozonant. EDU, even at the highest concentration, never caused evidence of phytotoxicity. Total peroxidase activity and photosynthetic capacity were not influenced by EDU per se but the obtained results showed that EDU allows the plant to avoid the oxidative stress and to maintain an efficient photosynthetic capacity after chronic exposure to ozone.