title: Increased ratio of electron transport to net assimilation rate supports elevated isoprenoid emission rate in eucalypts under drought.
abstract: Plants undergoing heat and low-CO2 stresses emit large amounts of volatile isoprenoids compared with those in stress-free conditions. One hypothesis posits that the balance between reducing power availability and its use in carbon assimilation determines constitutive isoprenoid emission rates in plants and potentially even their maximum emission capacity under brief periods of stress. To test this, we used abiotic stresses to manipulate the availability of reducing power. Specifically, we examined the effects of mild to severe drought on photosynthetic electron transport rate (ETR) and net carbon assimilation rate (NAR) and the relationship between estimated energy pools and constitutive volatile isoprenoid emission rates in two species of eucalypts: Eucalyptus occidentalis (drought tolerant) and Eucalyptus camaldulensis (drought sensitive). Isoprenoid emission rates were insensitive to mild drought, and the rates increased when the decline in NAR reached a certain species-specific threshold. ETR was sustained under drought and the ETR-NAR ratio increased, driving constitutive isoprenoid emission until severe drought caused carbon limitation of the methylerythritol phosphate pathway. The estimated residual reducing power unused for carbon assimilation, based on the energetic status model, significantly correlated with constitutive isoprenoid emission rates across gradients of drought (r(2) > 0.8) and photorespiratory stress (r(2) > 0.9). Carbon availability could critically limit emission rates under severe drought and photorespiratory stresses. Under most instances of moderate abiotic stress levels, increased isoprenoid emission rates compete with photorespiration for the residual reducing power not invested in carbon assimilation. A similar mechanism also explains the individual positive effects of low-CO2, heat, and drought stresses on isoprenoid emission.
authors.affiliation: Department of Biological Sciences (K.G.S.D., I.C.P., B.J.A.) and Department of Chemistry and Biomolecular Sciences (K.G.S.D., I.M.J.), Macquarie University, North Ryde, Sydney, New South Wales 2109, Australia; andGrantham Institute for Climate Change and Grand Challenges in Ecosystems and Environment, Department of Life Sciences, Imperial College London, Ascot SL5 7PY, United Kingdom (I.C.P.).
authors.forename: Kaidala Ganesha Srikanta
authors.initials: KG
authors.lastname: Dani
authors.affiliation: Department of Biological Sciences (K.G.S.D., I.C.P., B.J.A.) and Department of Chemistry and Biomolecular Sciences (K.G.S.D., I.M.J.), Macquarie University, North Ryde, Sydney, New South Wales 2109, Australia; andGrantham Institute for Climate Change and Grand Challenges in Ecosystems and Environment, Department of Life Sciences, Imperial College London, Ascot SL5 7PY, United Kingdom (I.C.P.).
authors.forename: Ian McLeod
authors.initials: IM
authors.lastname: Jamie
authors.affiliation: Department of Biological Sciences (K.G.S.D., I.C.P., B.J.A.) and Department of Chemistry and Biomolecular Sciences (K.G.S.D., I.M.J.), Macquarie University, North Ryde, Sydney, New South Wales 2109, Australia; andGrantham Institute for Climate Change and Grand Challenges in Ecosystems and Environment, Department of Life Sciences, Imperial College London, Ascot SL5 7PY, United Kingdom (I.C.P.).
authors.forename: Iain Colin
authors.initials: IC
authors.lastname: Prentice
authors.affiliation: Department of Biological Sciences (K.G.S.D., I.C.P., B.J.A.) and Department of Chemistry and Biomolecular Sciences (K.G.S.D., I.M.J.), Macquarie University, North Ryde, Sydney, New South Wales 2109, Australia; andGrantham Institute for Climate Change and Grand Challenges in Ecosystems and Environment, Department of Life Sciences, Imperial College London, Ascot SL5 7PY, United Kingdom (I.C.P.) brian.atwell@mq.edu.au.
authors.forename: Brian James
authors.initials: BJ
authors.lastname: Atwell
mesh_terms: D055864:Droughts; D004579:Electron Transport; D005052:Eucalyptus / Q000378:metabolism*; D018515:Plant Leaves / Q000378:metabolism; D013729:Terpenes / Q000378:metabolism*
chemical_list: D013729:Terpenes