PREDISPOSITION OF TOBACCO TO OZONE DAMAGE

Abstract

Effects of ontogeny, genome, nitrogen, and water supplies and ozone itself in predisposing tobacco plants to ozone damage (including weather fleck) are described from experiments in both field and greenhouse. The fully expanded leaf became susceptible to low doses of ozone at the time its protein content started to fall. Topping slowed the development of susceptibility of leaves, with the result that the susceptibility of the plants was decreased. Effects of genome were at least partly of an ontogenetic nature. Susceptibility was enhanced by both deficiency and excess of nitrogen. Moisture prior to fumigation increased susceptibility. Long term effects of moisture supply were akin to its influence on drought-hardiness. Susceptibility was increased by shortened photoperiod, low day temperature, and high night temperature, indicating a protective influence of photosynthat. A large or a small dose of ozone appeared to predispose against or toward, respectively; susceptibility to the next dose. Wherever tested, stomatal opening was positively associated with damage. Since stomatal opening regulates the flux of ozone into the leaf, it controls the amount of damage to tissue of a given degree of susceptibility.