Tropospheric ozone produces symptoms such as leaf injury in Nicotiana tabacum. Tobacco cultivars are often used as ozone indicators in air-quality biomonitoring programs. Bel-W3 (sensitive) and Bel-B (tolerant) cultivars are better known. The aim of this study was to verify if the two cultivars show variation in leaf structure that may help to explain differences in ozone sensitivity. Expanded leaves from plants growing in pollutant-free air were collected, processed according to the usual techniques of plant anatomy, and analyzed quantitatively and qualitatively. The sensitive cultivar showed lower stomatal density on the abaxial leaf surface and thicker mesophyll cells when compared to the tolerant cultivar. Qualitatively speaking, both cultivars had healthy cells with unaltered vacuoles. In the sensitive cultivar, we could see more intercellular spaces, larger substomatal chambers and slightly prominent stomata on both leaf surfaces. From a structural view point, these features explain why cultivar Bel-W3 is more sensitive.
leaf anatomy; ozone; tobacco Bel-W3; tobacco Bel-B
