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

A role of non-glandular emergences in avoiding ozone (O-3) damages by preventing its entrance into leaf tissues has been suggested in the O-3-tolerant species Croton floribundus (Euphorbiaceae). However, this function against O-3 damage has been underestimated due to the covering wax layer, mostly composed of saturated hydrocarbon, which has low O-3 reactivity. To evaluate the role of these emergences in conferring tolerance to O-3, we mechanically removed the non-glandular emergences from leaf blades of C. floribundus, submitted the plants to acute O-3 fumigation, and assessed morphological and microscopic alterations. Plants with intact leaves treated with O-3 showed the same phenotype as control samples but showed microscopic indicators of accelerated senescence. These alterations indicated a whole-plant response to O-3. In contrast, plants whose leaves had got their emergences removed exhibited specific morphological symptoms as well as microscopic O-3 damage. We thus conclude that the leaf emergences constitute a barrier for volatile contention, preventing O-3 damage to leaf tissues in C. floribundus. When these structures have been removed, defense volatiles are possibly quickly dispersed, makes this species vulnerable to O-3. This study highlights the relevance of surface structures for plant resistance to O-3 damages, complementing biochemical defenses.