Troposphere ozone (O3) is an important photochemical pollutant due to its high reactivity and phytotoxicity. Plants can show microscopic damage caused by this gas before the detection of visible symptoms. The present study aimed to improve our knowledge concerning the effects of O3 on Ipomoea nil L. cv. Scarlet O'Hara leaves. Plants were exposed at a pollutant site in São Paulo city, with high levels of O3, and fumigation with O3 was also carried out. In plants exposed to the environment, without visible symptoms, hypersensitive response-like (HR-like) and protrusions in the cell walls was observed, indicating oxidative processes; in leaves with visible symptoms, there is epidermis breakdown and the palisade and spongy parenchyma collapse. Fumigation confirmed that microscopic damage occurring in the plants exposed to the environment was linked to the symptoms caused by O3. These results demonstrate that Ipomoea nil responds to stress induced by O3 with specific structural changes that precede visible symptoms.
ozone; HR-like; cell wall protrusions; microscopic damage
