Structural and physiological responses to ozone in Manna ash (Fraxinus ornus L.) leaves of seedlings and mature trees under controlled and ambient conditions

Abstract

Leaf-level microscopical symptom structure and physiological responses were investigated in seedlings experimentally exposed to ozone (O3) in indoor chambers (150 ppb, 8 h d(-1)/7 weeks), and field trees of Manna ash (Fraxinus ornus) exposed to ambient O3 (max 93 ppb/one growing season). Ozone-induced leaf injury, including leaf reddening and stippling, was observed in both seedlings and mature trees, but the morphology of injury in the stipples differed, being hypersensitive-like (HR-like) in the chamber seedlings and accelerated cell senescence (ACS) in the field trees. In both exposure conditions, the main structural impact of O3 was on the mesophyll and especially the upper assimilating cell layers. The main physiological impact was on carbon assimilation and on stomatal sluggishness. These effects were not due to stomatal structural injury and were more severe in juvenile compared to mature trees because of environmental (water availability, light) and constitutional (gas exchange capacity) factors and differences in the cell physiology processes (HR-like vs. ACS) triggered by ozone stress. Given the plasticity of plant responses to ozone stress, dose/response relationships for tree seedlings in the indoor chambers cannot be extrapolated to mature trees unless ambient conditions are closely simulated.

Effects of elevated ozone on physiological, anatomical and ultrastructural characteristics of four common urban tree species in China

“…OB triggers programmed death, leading to a cell collapse as observed in stippling areas in AA and PO. As shown in the present study, palisade parenchyma is usually the most affected tissue by O 3 (Günthardt-Goerg and Vollenweider, 2007;Paoletti et al, 2009). Our observations suggest that reactive oxygen species (ROS) degrades the pectins of the middle lamella inducing a separation of the mesophyll cells, and increasing intercellular spaces.…”

Determinants of stomatal sluggishness in ozone-exposed deciduous tree species

“…Maier-Maercker (1989) suggested that such slower stomatal response might be explained by delignification of the guard cell and subsidiary cells as recorded in ozonated Picea abies. No change in guard cell wall lignification, however, was observed in ozone-injured manna ash (Fraxinus ornus) leaves showing stomatal sluggishness (Paoletti et al, 2009). In manna ash, such slower stomatal responses were considered as accelerated senescence in the cell physiological processes (Paoletti et al, 2009).…”

“…No change in guard cell wall lignification, however, was observed in ozone-injured manna ash (Fraxinus ornus) leaves showing stomatal sluggishness (Paoletti et al, 2009). In manna ash, such slower stomatal responses were considered as accelerated senescence in the cell physiological processes (Paoletti et al, 2009). Mills et al (2009) found that O 3 reduced stomatal sensitivity to ABA.…”

“…Ozone has been reported to induce stomatal closure (Wittig et al, 2007). However, slower or less efficient stomatal control may occur, especially a weaker ability to close stomata, referred to as "O 3 -induced stomatal sluggishness" (Paoletti, 2005;Mills et al, 2009;Paoletti et al, 2009;Paoletti and Grulke, 2010;Hoshika et al, 2012aHoshika et al, , 2013aDumont et al, 2013). Sluggishness may occur because O 3 reduces stomatal sensitivity to abscisic acid (ABA) (Mills et al, 2009).…”

Elevated ozone negatively affects photosynthesis of current-year leaves but not previous-year leaves in evergreen Cyclobalanopsis glauca seedlings

“…photosynthesis (Bagard et al, 2008;Feng et al, 2011;Schaub et al, 2005;Wittig et al, 2009;Zhang et al, 2010). The reduction in photosynthesis rate by O 3 could be attributed to stomatal closure, decreased chlorophyll content and electron transport rate, impaired carboxylation capacity and Rubisco content (Paoletti et al, 2009;Reich, 1983). Although the reduction in Rubisco activity was assumed to be the primary cause in photosynthetic decline under O 3 stress, stoma appeared to an important factor controlling O 3 entering the leaf interior (Novak et al, 2005).…”