Isoprene emission protects photosynthesis but reduces plant productivity during drought in transgenic tobacco (<i>Nicotiana tabacum</i>) plants

<jats:title>Summary</jats:title><jats:p> <jats:list list-type="bullet"> <jats:list-item><jats:p>Isoprene protects the photosynthetic apparatus of isoprene‐emitting plants from oxidative stress. The role of isoprene in the response of plants to drought is less clear.</jats:p></jats:list-item> <jats:list-item><jats:p>Water was withheld from transgenic isoprene‐emitting and non‐emitting tobacco (<jats:italic>Nicotiana tabacum</jats:italic>) plants, to examine: the response of isoprene emission to plant water deficit; a possible relationship between concentrations of the drought‐induced phytohormone abscisic acid (<jats:styled-content style="fixed-case">ABA</jats:styled-content>) and isoprene; and whether isoprene affected foliar reactive oxygen species (<jats:styled-content style="fixed-case">ROS</jats:styled-content>) and lipid peroxidation levels.</jats:p></jats:list-item> <jats:list-item><jats:p>Isoprene emission did not affect whole‐plant water use, foliar <jats:styled-content style="fixed-case">ABA</jats:styled-content> concentration or leaf water potential under water deficit. Compared with well‐watered controls, droughted non‐emitting plants significantly increased <jats:styled-content style="fixed-case">ROS</jats:styled-content> content (31–46%) and lipid peroxidation (30–47%), concomitant with decreased operating and maximum efficiencies of photosystem <jats:styled-content style="fixed-case">II</jats:styled-content> photochemistry and lower leaf and whole‐plant water use efficiency (<jats:styled-content style="fixed-case">WUE</jats:styled-content>). Droughted isoprene‐emitting plants showed no increase in <jats:styled-content style="fixed-case">ROS</jats:styled-content> content or lipid peroxidation relative to well‐watered controls, despite isoprene emission decreasing before leaf wilting.</jats:p></jats:list-item> <jats:list-item><jats:p>Although isoprene emission protected the photosynthetic apparatus and enhanced leaf and whole‐plant <jats:styled-content style="fixed-case">WUE</jats:styled-content>, non‐emitting plants had 8–24% more biomass under drought, implying that isoprene emission incurred a yield penalty.</jats:p></jats:list-item> </jats:list> </jats:p>