PHYSIOLOGICAL-CHARACTERISTICS OF TOBACCO CULTIVARS WITH CONTRASTING SENSITIVITY TO OZONE

Two cultivars of tobacco with contrasting sensitivity to ozone have si milar photosynthesis at low light intensity, but at high light, photos ynthesis of the sensitive cultivar Bel-W3 was lower than that of the r esistant cultivar Havana. In contrast, the electron transport rate at photosynthesis saturated light intensity was higher in Bel-W3 than in Havana. This excess may require efficient mechanisms to dissipate ener gy and oxygen radicals. We found that the non-radiative dissipation wa s lower in Bel-W3 than in Havana and that the conversion between viola xanthin and anther-axanthin+zeaxanthin was not complete in the ozone s ensitive cultivar. Violaxanthin may have been partly converted in ABA. The high content of ABA may have caused stomatal closure and explain why photosynthesis at high light was reduced in Bel-W3 in comparison t o Havana. beta-Carotene content was also lower in Bel-W3 than in Havan a. A low beta-carotene content coupled with an inefficient use of the xanthophyll mechanism may contribute to determine the ozone sensitivit y of Bel-W3 leaves. (C) 1997 Published by Elsevier Science B.V.