Abstract
The effects of O3 on visible injury and stomatal conductance for water vapor transfer were determined during the leaf development of sunflower plant (Helianthus annuus L. cv. Russian Mammoth) . The stomatal frequency and conductance were also measured during the leaf development. The foliar necrosis induced by the exposure to O3 was influenced by the leaf age. With increasing leaf age, the foliar necrosis increased from young to mature leaves, then decreased in senescent leaves. The effect on stomatal conductance was also influenced. The inhibition of stomatal conductance on the pretreatment value basis decreased from young to senescent leaves. The degree of foliar necrosis had no linear relationship to the calculated uptake rate of O3 suggesting that the agedependent foliar sensitivity to O3 could not be determined by the amount of O3 incorporated into leaves but by the detoxicating capacity of absorbed O3 in the leaf.
