Response of Plants to Air Pollutants. III. A Relation between Ascorbic Acid Levels and Ozone Susceptibility of Light-Preconditioned Tobacco Plants.

The effects of prefumigation light regimes on plants indicate that light modifies the response of plants to ozone. Taylor et al. (11) reportecl that ozone injury to Pinto bean was reduced when plants were grown at the higher level of 2 light intensities. Menser et al. (7) foundl that ozone danmage to tobacco plants was diminished by an extendedl 22-hour photoperiod immediately before funmigation. Ascorbic acid is known to protect plants from ozone and other oxidizing agents. Freebairn (3) increased the tolerance of Pinto bean plants to ozone either by supplying ascorbic acid to the roots or by foliar applications. Freebairn and Taylor (4) nmade tissue analysis of smog-sensitive plants spraye(d with ascorbic acid. They found that concentrations of ascorbic acidl in the leaves increased and resultedl in partial to conmplete protection fronm air-pollution injury. This paper presents results of a study to determine the effects of light preconditioning on ascorbic acid levels in tobacco plants; andl the relation of ascorbic acid levels to ozone injury of 2 tobacco varieties, one resistant and the other sensitive to ozone. Ascorbic aci(l concentrations reported represent the excess formledl in synthesis over that utilized in metabolism. The results shoxv that light preconditioning caused notable differences in ascorbic acidl levels. These differences were associated vith chainges in the degree of ozone injury.