title: Determination of the site of CO₂ sensing in poplar: is the area-based N content and anatomy of new leaves determined by their immediate CO₂ environment or by the CO₂ environment of mature leaves?
abstract: Exposure to an elevated CO(2) concentration ([CO(2)]) generally decreases leaf N content per unit area (N(area)) and stomatal density, and increases leaf thickness. Mature leaves can 'sense' elevated [CO(2)] and this regulates stomatal development of expanding leaves (systemic regulation). It is unclear if systemic regulation is involved in determination of leaf thickness and N(area)-traits that are significantly correlated with photosynthetic capacity. A cuvette system was used whereby [CO(2)] around mature leaves was controlled separately from that around expanding leaves. Expanding leaves of poplar (Populus trichocarpa×P. deltoides) seedlings were exposed to elevated [CO(2)] (720 μmol mol(-1)) while the remaining mature leaves inside the cuvette were under ambient [CO(2)] of 360 μmol mol(-1). Reverse treatments were performed. Exposure of newly developing leaves to elevated [CO(2)] increased their thickness, but when mature leaves were exposed to elevated [CO(2)] the increase in thickness of new leaves was less pronounced. The largest response to [CO(2)] was reflected in the palisade tissue thickness (as opposed to the spongy tissue) of new leaves. The N(area) of new leaves was unaffected by the local [CO(2)] where the new leaves developed, but decreased following the exposure of mature leaves to elevated [CO(2)]. The volume fraction of mesophyll cells compared with total leaf and the mesophyll cell density changed in a manner similar to the response of N(area). These results suggest that N(area) is controlled independently of the leaf thickness, and suggest that N(area) is under systemic regulation by [CO(2)] signals from mature leaves that control mesophyll cell division.
authors.affiliation: Centre for Forest Biology, Department of Biology, University of Victoria, PO Box 3020, Victoria, BC V8W3N5, Canada. miyashin@affrc.go.jp
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Miyazawa
authors.forename: Charles R
authors.initials: CR
authors.lastname: Warren
authors.forename: David H
authors.initials: DH
authors.lastname: Turpin
authors.forename: Nigel J
authors.initials: NJ
authors.lastname: Livingston
mesh_terms: D000704:Analysis of Variance; D002245:Carbon Dioxide / Q000494:pharmacology*; D004777:Environment; D058503:Mesophyll Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism*; D018515:Plant Leaves / Q000033:anatomy & histology* / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development; D032107:Populus / Q000033:anatomy & histology* / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D009584:Nitrogen