title: Overexpression of the barley aquaporin HvPIP2;1 increases internal CO(2) conductance and CO(2) assimilation in the leaves of transgenic rice plants.
abstract: The internal conductance for CO(2) diffusion (g(i)) and CO(2) assimilation rate were measured and the related anatomical characteristics were investigated in transgenic rice leaves that overexpressed barley aquaporin HvPIP2;1. This study was performed to test the hypothesis that aquaporin facilitates CO(2) diffusion within leaves. The g(i) value was estimated for intact leaves by concurrent measurements of gas exchange and carbon isotope ratio. The leaves of the transgenic rice plants that expressed the highest levels of Aq-anti-HvPIP2;1 showed a 40% increase in g(i) as compared to g(i) in the leaves of wild-type rice plants. The increase in g(i) was accompanied by a 14% increase in CO(2) assimilation rate and a 27% increase in stomatal conductance (g(s)). The transgenic plants that had low levels of Aq-anti-HvPIP2;1 showed decreases in g(i) and CO(2) assimilation rate. In the plants with high levels of Aq-anti-HvPIP2;1, mesophyll cell size decreased and the cell walls of the epidermis and mesophyll cells thickened, indicating that the leaves had become xeromorphic. Although such anatomical changes could partially offset the increase in g(i) by the aquaporin, the increase in aquaporin content overcame such adverse effects.
authors.affiliation: Research Institute for Bioresources, Okayama University, Kurashiki, 710-0046 Japan. hanba@rib.okayama-u.ac.jp
authors.forename: Yuko T
authors.initials: YT
authors.lastname: Hanba
authors.forename: Mineo
authors.initials: M
authors.lastname: Shibasaka
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Hayashi
authors.forename: Takahiko
authors.initials: T
authors.lastname: Hayakawa
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Kasamo
authors.forename: Ichiro
authors.initials: I
authors.lastname: Terashima
authors.forename: Maki
authors.initials: M
authors.lastname: Katsuhara
mesh_terms: D020346:Aquaporins / Q000235:genetics / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism*; D019069:Cell Respiration / Q000235:genetics; D002473:Cell Wall / Q000235:genetics / Q000378:metabolism / Q000648:ultrastructure; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D004058:Diffusion; D018506:Gene Expression Regulation, Plant / Q000235:genetics; D001467:Hordeum / Q000235:genetics / Q000378:metabolism*; D012275:Oryza / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D010788:Photosynthesis / Q000235:genetics; D019441:Plant Epidermis / Q000166:cytology / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000166:cytology / Q000235:genetics / Q000378:metabolism*; D015854:Up-Regulation / Q000235:genetics
chemical_list: D020346:Aquaporins; D010940:Plant Proteins; C110065:major intrinsic protein, plant; D002245:Carbon Dioxide