Annual Review of Plant Physiology and Plant Molecular Biology · 2001 · 621 citations · 148 references
Life SciencesPlant BiologyPlant SciencesPhotosynthesisPlant BiochemistryPlant PhysiologyChloroplast BiochemistryChloroplast BioenergeticsEnvironmental Responses Of PhotosynthesisPlant Gas ExchangePlant MetabolismHeat CapacityHydrocarbon FluxIsoprene EmissionsIsoprenoidsLow-temperature Heat Capacity
Very large amounts of isoprene are emitted from vegetation, especially mosses, ferns, and trees, and this hydrocarbon flux, roughly equal to methane, significantly affects atmospheric oxidizing potential. Researchers hypothesize that plants benefit from isoprene emission because it helps photosynthesis recover from short high‑temperature episodes. Isoprene is synthesized de novo via the DXP/MEP pathway in plastids, where dimethylallyl pyrophosphate is converted to isoprene by isoprene synthase, an enzyme with a high pH optimum and Mg²⁺ requirement consistent with chloroplast localization. Isoprene emission incurs significant carbon, ATP, and reducing power costs to the plant, yet may have evolved to enable survival during rapid temperature changes due to its low heat capacity relative to water.
Very large amounts of isoprene are emitted from vegetation, especially from mosses, ferns, and trees. This hydrocarbon flux to the atmosphere, roughly equal to the flux of methane, has a large effect on the oxidizing potential of the atmosphere. Isoprene emission results from de novo synthesis by the deoxyxylulose phosphate/methyl erythritol 4-phosphate pathway in plastids. Dimethylallyl pyrophosphate made by this pathway is converted to isoprene by isoprene synthase. Isoprene synthase activity in plants has a high pH optimum and requirement for Mg2+ that is consistent with its location inside chloroplasts. Isoprene emission costs the plant significant amounts of carbon, ATP, and reducing power. Researchers hypothesize that plants benefit from isoprene emission because it helps photosynthesis recover from short high-temperature episodes. The evolution of isoprene emission may have been important in allowing plants to survive the rapid temperature changes that can occur in air because of the very low heat capacity of isoprene relative to water.
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