Biogenic Volatile Organic Compounds Emission of Brazilian Atlantic Tree Grown Under Elevated Ozone in Ambient Controlled and Field Conditions.

Croton floribundus (L.) Spreng trees were exposed to accumulated ozone (O3) levels under laboratory and field conditions and monitored the foliar visible symptoms and BVOC emissions. Plants exposed to O3 in the laboratory presented more substantial damage and significant increase in the BVOC emissions than plants in the field. Caryophyllene and 3-hexen-1-ol emissions were significantly increased in plants exposed to O3 in the laboratory. Under field conditions, methyl salicylate (MeSA) was the majority compound emitted. A positive correlation among the meteorological conditions, O3 and MeSA emission was observed in the field conditions, which may represent a mechanism of tolerance by C. floribundus to deal with long-term exposure to O3.

Ozone-induced responses in Croton floribundus Spreng. (Euphorbiaceae): metabolic cross-talk between volatile organic compounds and calcium oxalate crystal formation.

Here, we proposed that volatile organic compounds (VOC), specifically methyl salicylate (MeSA), mediate the formation of calcium oxalate crystals (COC) in the defence against ozone (O3) oxidative damage. We performed experiments using Croton floribundus, a pioneer tree species that is tolerant to O3 and widely distributed in the Brazilian forest. This species constitutively produces COC. We exposed plants to a controlled fumigation experiment and assessed biochemical, physiological, and morphological parameters. O3 induced a significant increase in the concentrations of constitutive oxygenated compounds, MeSA and terpenoids as well as in COC number. Our analysis supported the hypothesis that ozone-induced VOC (mainly MeSA) regulate ROS formation in a way that promotes the opening of calcium channels and the subsequent formation of COC in a fast and stable manner to stop the consequences of the reactive oxygen species in the tissue, indeed immobilising the excess calcium (caused by acute exposition to O3) that can be dangerous to the plant. To test this hypothesis, we performed an independent experiment spraying MeSA over C. floribundus plants and observed an increase in the number of COC, indicating that this compound has a potential to directly induce their formation. Thus, the tolerance of C. floribundus to O3 oxidative stress could be a consequence of a higher capacity for the production of VOC and COC rather than the modulation of antioxidant balance. We also present some insights into constitutive morphological features that may be related to the tolerance that this species exhibits to O3.