title: Photoassimilation, assimilate translocation and plasmodesmal biogenesis in the source leaves of Arabidopsis thaliana grown under an increased atmospheric CO2 concentration.
abstract: Using 18-day-old Arabidopsis thaliana seedlings grown under increased (780 p.p.m., experimental plants) or ambient (390 p.p.m., control plants) CO2 conditions, we evaluated (14)CO2 photoassimilation in and translocation from representative source leaves. The total (14)CO2 photoassimilation amounts increased in the third leaves of the experimental plants in comparison with that found for the third leaves of the control plants, but the rates were comparable for the first leaves of the two groups. In contrast, translocation of labeled assimilates doubled in the first leaves of the experimental group, whereas translocation was, at best, passively enhanced even though photoassimilation increased in their third leaves. The transcript levels of the companion cell-specific sucrose:H(+) symporter gene SUC2 were not significantly affected in the two groups of plants, whereas those of the sucrose effluxer gene SWEET12 and the sieve element-targeted sucrose:H(+) symporter gene SUT4 were up-regulated in the experimental plants, suggesting up-regulation of SUT4-dependent apoplastic phloem loading. Compared with SUC2, SUT4 is a minor component that is expressed in companion cells but functions in sieve elements after transfer through plasmodesmata. The number of aniline blue-stained spots for plasmodesma-associated callose in the midrib wall increased in the first leaf of the experimental plants but was comparable in the third leaf between the experimental and control plants. These results suggest that A. thaliana responds to greater than normal concentrations of CO2 differentially in the first and third leaves in regards to photoassimilation, assimilate translocation and plasmodesmal biogenesis.
authors.affiliation: Laboratory of Plant Molecular Physiology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, Shimo-Okubo 255, Sakura-Ku, Saitama, 338-8570 Japan.
authors.forename: Zhongrui
authors.initials: Z
authors.lastname: Duan
authors.forename: Ayumi
authors.initials: A
authors.lastname: Homma
authors.forename: Megumi
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Noriko
authors.initials: N
authors.lastname: Nagata
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Kaneko
authors.forename: Yuki
authors.initials: Y
authors.lastname: Fujiki
authors.forename: Ikuo
authors.initials: I
authors.lastname: Nishida
mesh_terms: D000814:Aniline Compounds; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D002245:Carbon Dioxide / Q000378:metabolism / Q000494:pharmacology*; D019069:Cell Respiration; D018506:Gene Expression Regulation, Plant; D005936:Glucans / Q000378:metabolism; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018613:Microscopy, Confocal; D008954:Models, Biological; D052585:Phloem / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D018515:Plant Leaves / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D018517:Plant Roots / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D031425:Plasmodesmata / Q000648:ultrastructure*; D036226:Seedlings / Q000187:drug effects / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D013395:Sucrose / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D000814:Aniline Compounds; D029681:Arabidopsis Proteins; D005936:Glucans; D026901:Membrane Transport Proteins; C512029:SUT4 protein, Arabidopsis; D002245:Carbon Dioxide; D013395:Sucrose; C017006:aniline blue; C048306:callose
keywords: Arabidopsis thaliana; CO2 atmospheric levels; Photoassimilate translocation; Plasmodesma formation