The role of non‐glandular emergences in Croton floribundus (Euphorbiaceae) upon elevated ozone exposures

A role of non‐glandular emergences in avoiding ozone (O₃) damages by preventing its entrance into leaf tissues has been suggested in the O₃‐tolerant species Croton floribundus (Euphorbiaceae). However, this function against O₃ damage has been underestimated due to the covering wax layer, mostly composed of saturated hydrocarbon, which has low O₃ reactivity. To evaluate the role of these emergences in conferring tolerance to O₃, we mechanically removed the non‐glandular emergences from leaf blades of C. floribundus, submitted the plants to acute O₃ fumigation, and assessed morphological and microscopic alterations. Plants with intact leaves treated with O₃ showed the same phenotype as control samples but showed microscopic indicators of accelerated senescence. These alterations indicated a whole‐plant response to O₃. In contrast, plants whose leaves had got their emergences removed exhibited specific morphological symptoms as well as microscopic O₃ damage. We thus conclude that the leaf emergences constitute a barrier for volatile contention, preventing O₃ damage to leaf tissues in C. floribundus. When these structures have been removed, defense volatiles are possibly quickly dispersed, makes this species vulnerable to O₃. This study highlights the relevance of surface structures for plant resistance to O₃ damages, complementing biochemical defenses.