Abstract
Ozone is a strong oxidant and a key stress elicitor. The immediate and longer term impacts of ozone are poorly understood in species with emission of both de novo synthesized and stored volatiles, such a tobacco (Nicotiana tabacum), which has terpene-containing glandular trichomes on the leaf surface. In this study, we exposed N. tabacum 'Wisconsin' leaves to acute ozone doses of 0 (control), 400, 600, 800, and 1000 ppb for 30 min and studied the effects of ozone exposure on ozone uptake, gas-exchange characteristics, and emissions of lipoxygenase pathway volatiles, monoterpenes, and sesquiterpenes. Foliage emissions of lipoxygenase pathway volatiles were quantitatively related to the severity of ozone exposure, but the stress dose vs. emission relationship was weaker for terpenoids. Analysis of leaf terpene content and composition indicated that several monoterpenes and sesquiterpenes were not stored in leaves and were synthesized de novo upon ozone exposure. The highest degree of elicitation for each compound was observed immediately after ozone treatment and it declined considerably during recovery. Leaf ozone uptake was dominated by non-stomatal deposition, and the emissions of total lipoxygenase pathway volatiles and mono- and sesquiterpenes were positively correlated with non-stomatal ozone deposition. Overall, this study demonstrates remarkably high ozone resistance of the studied tobacco cultivar and indicates that ozone's effects on volatile emissions primarily reflect modifications in the release of stored volatiles and reaction of ozone with the leaf surface structure.
Highlights
Ozone (O3) is a phytotoxic gas that leads to major losses of vegetation productivity worldwide (Fares et al, 2010b)
Leaf ozone uptake was dominated by non-stomatal deposition, and the emissions of total lipoxygenase pathway volatiles and monoand sesquiterpenes were positively correlated with non-stomatal ozone deposition
The blend of emitted monoterpenes was dominated by limonene, followed by α-pinene, β-pinene, Δ3-carene, and camphene (Fig. 5), whereas α-caryophyllene was observed as the main sesquiterpene (Fig. 6A)
Summary
Ozone (O3) is a phytotoxic gas that leads to major losses of vegetation productivity worldwide (Fares et al, 2010b). Tropospheric ozone concentration over most of the terrestrial surface is between 20 and 45 ppb (Sicard et al, 2017), but in local pollution hotspots, much higher concentrations can be observed, e.g. in major industrial cities in China, the ozone concentration is ca 70 ppb (Yuan et al, 2015) and in industrial cities in India, it is ca 50–60 ppb (Sharma et al, 2013). Plants act as a sink for ozone in two ways: stomatal uptake and non-stomatal deposition (Altimir et al, 2006; Fares et al, 2010b). Stomatal uptake is the primary route for ozone into the leaf mesophyll cells (Fares et al, 2008). Ozone, as a strong oxidant, can result in major oxidative stress (Schwanz et al, 1996; Calfapietra et al, 2013)
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