Stomatal and Leaf Surface Features as Related to the Ozone Sensitivity of Petunia Cultivars1

Abstract

Abstract Under the light microscope the stomata of 3 cultivars of Petunia hybrida Vilm. were similar in shape and type. However, scanning electron microscopic examination of ‘White Cascade’ petunia (O 3 sensitive) revealed guard cell cuticle was not raised above the epidermal surface. ‘Capri’ (O 3 insensitive) had the greatest number of stomata/mm 2 and the shortest pore length whereas ‘White Cascade’ had the lowest number but the longest pore length. The cultivar with intermediate O 3 sensitivity, ‘White Magic’, had an intermediate stomatal density and pore size. The stomatal pore area (mm 2 /mm 2 leaf surface area) was found to be about equal in all 3 cultivars. ‘Capri’ had many more trichomes per unit area than ‘White Cascade’ while ‘White Magic’ had intermediate numbers. No major differences existed in leaf diffusive resistance among the cvs. in either light or dark. The O 3 insensitivity of ‘Capri’ was not explained by inherently fewer stomata and/or smaller stomatal size and/or greater leaf diffusive resistance than those of the sensitive ‘White Cascade’. Number of trichomes, sizes of epidermal cells and configuration of guard cell cuticle in relation to epidermal cells may be related to sensitivity.