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The sessile nature of plants has resulted in the evolution of an extraordinarily diverse suite of protective mechanisms against biotic and abiotic stresses. Though volatile isoprenoids are known to be involved in many types of biotic interactions, they also play important but relatively unappreciated roles in abiotic stress responses. We review those roles, discuss the proposed mechanistic explanations and examine the evolutionary significance of volatile isoprenoid emission. We note that abiotic stress responses generically involve production of reactive oxygen species in plant cells, and volatile isoprenoids mitigate the effects of oxidative stress by mediating the oxidative status of the plant. On the basis of these observations, we propose a 'single biochemical mechanism for multiple physiological stressors' model, whereby the protective effect against abiotic stress is exerted through direct or indirect improvement in resistance to damage by reactive oxygen species.

Nonmethane hydrocarbons are ubiquitous trace atmospheric constituents yet they control the oxidation capacity of the atmosphere. Both anthropogenic and biogenic processes contribute to the release of hydrocarbons to the atmosphere. In this manuscript, the state of the science concerning biosynthesis, transport, and chemical transformation of hydrocarbons emitted by the terrestrial biosphere is reviewed. In particular, the focus is on isoprene, monoterpenes, and oxygenated hydrocarbons. The generated science during the last 10 years is reviewed to explain and quantify hydrocarbon emissions from vegetation and to discern impacts of biogenic hydrocarbons on local and regional atmospheric chemistry. Furthermore, the physiological and environmental processes controlling biosynthesis and production of hydrocarbon compounds are reported on. Many advances have been made on measurement and modeling approaches developed to quantify hydrocarbon emissions from leaves and forest ecosystems. A synthesis of the atmospheric chemistry of biogenic hydrocarbons and their role in the formation of oxidants and aerosols is presented. The integration of biogenic hydrocarbon kinetics and atmospheric physics into mathematical modeling systems is examined to assess the contribution of biogenic hydrocarbons to the formation of oxidants and aerosols, thereby allowing us to study their impacts on the earth's climate system and to develop strategies to reduce oxidant precursors in affected regions. 1538

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