Sugar Content and Stomatal Width as Related to Ozone Injury in Tobacco Leaves

The extent of visual damage on leaves of Nicotiana tabacum, var. White Gold, treated with ozone under controlled environmental conditions, was found to be associated with the levels of sucrose and reducing sugars and the width of stomatal openings of the leaf. Leaves containing 5–14 mg sucrose per g dry weight were more susceptible than those of higher sucrose content. Leaves with 5–35 mg reducing sugars per g dry weight were also more sensitive to ozone than those with lower reducing sugar content. Introducing soluble sugars into the leaf varied sensitivity to ozone depending on the concentration of sugars, duration of sugar treatment, and conditions of the leaf itself. Ozone damage was positively correlated with the width of stomatal opening; but under certain conditions stomatal closure did not prevent leaf injury. High levels of sucrose and reducing sugars were associated with closure of stomata. Independently of the osmotic effect on stomatal movement, increasing sucrose content beyond the optimum for high sensitivity prevented damage from ozone.