PARENT SESSION
Poster Session #28: Gas Exchange.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

The role of stored carbon in isoprene production in response to environmental stress in Populus deltoides.

Funk, Jennifer^*,1, Mak, John², Lerdau, Manuel¹, ¹ Department of Ecology and Evolution, Stony Brook, NY² Marine Sciences Research Center, Stony Brook, NY

ABSTRACT- Isoprene is emitted from leaves of numerous plant species and has important implications for both plant metabolism and atmospheric chemistry. It has been suggested that, in the absence of photosynthesis, isoprene emission may continue as precursors are derived from stored carbon. The ability to use stored carbon for isoprene production may be important as plants often experience photosynthetic depression in response to environmental stress. We used stable isotopes of carbon to examine the role of stored carbon in isoprene production in Populus deltoides during water stress and conditions of high leaf temperature. Assuming an atmospheric CO₂ source of -8 ‰, we found the ¹³C of isoprene to be variable (-22 to -36 ‰), becoming isotopically depleted in severely water stressed individuals. In water stress and temperature experiments, a shift in isoprene composition from recently acquired carbon to stored carbon was observed only under severe water stress (stomatal conductance <0.02 mol m^-2 s^-1). The preferential incorporation of photosynthate into isoprene production occurred despite ~50% decreases in photosynthesis in stressed plants. Isoprene emission remained unchanged in response to water stress and increased exponentially with temperature. The differential incorporation of stored carbon into isoprene emission under severe water stress versus high leaf temperature suggests a complex relationship between the availability of isoprene precursors and leaf/whole-plant carbon status. Given this inconsistency, it is unclear how leaf-level models of isoprene emission will benefit from the incorporation of a parameter describing leaf or whole-plant carbon status.

KEY WORDS: isoprene, stable isotope, Populus, chloroplast metabolism