“…Exposure of alfalfa to high ozone concentrations (85-120 ppb) causes obvious effects on cell organelles such as chloroplasts, plastoglobules, nuclei, vacuoles and chromatin in leaf mesophyll tissue and stem cortex, and no clear effects of ozone were noted on starch grain shapes and the mitochondria in the leaf mesophyll and stem cortex cells (El-Zaidy et al, 2019). The stomatal density in the leaf epidermis of different plants was affected by elevated O 3 concentration (Evans et al, 1996;Paakkonen et al, 1998;Frey et al, 1996;Lawson et al, 2002;Zouzoulas et al, 2009;Gostin, 2009;Wahid and Ahmad, 2003;Pedroso and Alves, 2008), and caused sluggishness stomata efficiency, and gradual loss in stomatal control over transpiration (Feng et al, 2018). However, few works indicated lack of significant impact on the stomatal density of certain plants when exposed to O 3 stress (Giacomo et al, 2010;Riikonen et al, 2010;Dumont et al, 2014).…”