The emission profile of volatile organic compounds (VOCs) and nitric oxide (NO) in young and mature leaves of Croton floribundus was assessed in plants exposed to filtered air (FA) and ozone-enriched filtered air (FA+O). After the period of exposure, leaves were enclosed in polyethylene terephthalate bags and VOCs were collected in young and mature leaves. Both young and mature leaves constitutively emitted the same VOC, but the concentrations were higher in young leaves. O exposure induced the emission of sesquiterpenes (mainly β-caryophyllene) known as antioxidant compounds that may scavenge O. Young leaves were the highest emitters of sesquiterpenes. O induced a rapid accumulation of NO in different tissues and leaf developmental stages; this accumulation was marked in palisade and spongy parenchyma cells in young and mature leaves, respectively. O altered the levels of the signaling compound methyl salicylate (MeSA). Moreover, our data showed that NO together with VOC emissions, such as geranyl acetate, α-cadiene, trans-farnesol, cis-β-farnesene, and MeSA, participate of plant defense mechanisms against the oxidative damage caused by O.

Volatile organic compounds (VOC) variation in Received: 12.09.2017; accepted: 8.03.2018 ABSTRACT -(Volatile organic compounds (VOC) variation in Croton fl oribundus (L.) Spreng. related to environmental conditions and ozone concentration in an urban forest of the city of São Paulo, São Paulo State, Brazil). Volatile organic compounds (VOC) are emitted by vegetation in response to different kinds of stress, such as herbivory, environmental conditions and air pollutants. The aim of this study was to identify the VOC emitted by seedlings of Croton fl oribundus (L.) Spreng. exposed to a polluted environment and analyze the relationship among classes of compounds emitted, ozone levels and changes in climate conditions. Two exposures were carried out, one in winter (June to August 2012) and another in summer (January to April 2013), in the Parque Estadual das Fontes do Ipiranga, city of São Paulo, São Paulo State, Brazil. We identifi ed 26 compounds that are grouped into oxygenates, aromatics, monoterpenes and sesquiterpenes. The emission of sesquiterpenes was inhibited in summer, while those of the oxygenated and aromatic compounds were induced. The emission of volatiles was correlated to ozone levels (AOT 40). Our results suggest that the levels of atmospheric ozone detected in the summer can increase the induction of oxygenates and reduce the emission of monoterpenes in C. fl oribundus plants. Keywords: abiotic factors, air pollutants, oxidative stress RESUMO -(Variação dos compostos orgânicos voláteis (COV) deCroton fl oribundus (L.) Spreng. às condições ambientais e concentração de ozônio em fl oresta urbana de São Paulo, SP, Brasil). Os compostos orgânicos voláteis (COV) são emitidos pela vegetação em resposta ao estresse, incluindo fatores como herbivoria, condições ambientais e poluentes aéreos. Os objetivos deste trabalho foram identifi car compostos orgânicos voláteis emitidos por plantas jovens de Croton fl oribundus (L.) Spreng. expostas em ambiente poluído e relacionar as classes dos compostos emitidos com os níveis de ozônio atmosférico e variações climáticas. Foram realizadas duas exposições em diferentes estações climáticas (inverno de 2012: junho a agosto e verão de 2013: janeiro a abril), no Parque Estadual das Fontes do Ipiranga, São Paulo, SP, Brasil. Foram identifi cados 26 compostos, agrupados em oxigenados, aromáticos, monoterpenos e sesquiterpenos. As emissões dos sesquiterpenos foram inibidas no verão, enquanto as dos oxigenados e aromáticos foram induzidas. Os voláteis foram relacionados com os níveis de ozônio (AOT 40). Os resultados sugerem que os níveis de ozônio atmosférico detectados no verão podem contribuir para aumentar a emissão dos compostos oxigenados e reduzir a emissão dos monoterpenos em plantas de C. fl oribundus. Palavras-chave: estresse oxidativo, fatores abióticos, poluentes atmosféricos

A role of non‐glandular emergences in avoiding ozone (O3) damages by preventing its entrance into leaf tissues has been suggested in the O3‐tolerant species Croton floribundus (Euphorbiaceae). However, this function against O3 damage has been underestimated due to the covering wax layer, mostly composed of saturated hydrocarbon, which has low O3 reactivity. To evaluate the role of these emergences in conferring tolerance to O3, we mechanically removed the non‐glandular emergences from leaf blades of C. floribundus, submitted the plants to acute O3 fumigation, and assessed morphological and microscopic alterations. Plants with intact leaves treated with O3 showed the same phenotype as control samples but showed microscopic indicators of accelerated senescence. These alterations indicated a whole‐plant response to O3. In contrast, plants whose leaves had got their emergences removed exhibited specific morphological symptoms as well as microscopic O3 damage. We thus conclude that the leaf emergences constitute a barrier for volatile contention, preventing O3 damage to leaf tissues in C. floribundus. When these structures have been removed, defense volatiles are possibly quickly dispersed, makes this species vulnerable to O3. This study highlights the relevance of surface structures for plant resistance to O3 damages, complementing biochemical defenses.

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In this study, we demonstrated that Tetranychus urticae Koch (Acari: Tetranychidae), a generalist herbivore, induces volatile organic compounds (VOC) in Croton floribundus Spreng., a pioneer species widely used in Brazilian urban area. We performed experiments to evaluate the quality and quantity of VOC emission at different times (two, six and 24 hours and within four and nine days) of infestation by T. urticae. Results show that C. floribundus emitted 23 volatiles after infestation, including monoterpene, sesquiterpene and green leaf volatiles. Significant differences were only detected between infested and non-infested plants after 24 hours of treatment, in particular methyl salicylate. In contrast, 3-hexen-1ol, linaool, geranyl acetone and caryophyllene seem to be inhibited by hourly infestation. The α-farnesene, methyl salicylate, 3-carene, 3-hexen-1ol benzoate and nerolidol were the main compounds induced after four infestation-days. This study highlights that VOCs blends in C. floribundus is depended on the feeding time-course of T. urticae and suggests that the VOC-mediated ecological interaction may be less efficient in a pioneer species.