Journal Article

Overexpression of the Barley Aquaporin HvPIP2;1 Increases Internal CO<sub>2</sub> Conductance and CO<sub>2</sub> Assimilation in the Leaves of Transgenic Rice Plants

Yuko T. Hanba, Mineo Shibasaka, Yasuyuki Hayashi, Takahiko Hayakawa, Kunihiro Kasamo, Ichiro Terashima and Maki Katsuhara

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 5, pages 521-529
Published in print May 2004 | ISSN: 0032-0781
Published online May 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch070
Overexpression of the Barley Aquaporin HvPIP2;1 Increases Internal CO2 Conductance and CO2 Assimilation in the Leaves of Transgenic Rice Plants

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  • Biochemistry
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The internal conductance for CO2 diffusion (gi) and CO2 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 CO2 diffusion within leaves. The gi 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 gi as compared to gi in the leaves of wild-type rice plants. The increase in gi was accompanied by a 14% increase in CO2 assimilation rate and a 27% increase in stomatal conductance (gs). The transgenic plants that had low levels of Aq-anti-HvPIP2;1 showed decreases in gi and CO2 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 gi by the aquaporin, the increase in aquaporin content overcame such adverse effects.

Keywords: Keywords: Aquaporin — CO2 assimilation rate — HvPIP2;1 — Mesophyll anatomy — Transgenic rice — Stomatal CO2 conductance.; Abbreviations: Aq-anti-HvPIP2;1, aquaporins detected by an antibody raised against HvPIP2;1; gi, internal CO2 conductance; gs, stomatal CO2 conductance; Ca, ambient CO2 partial pressure; Cc, chloroplast CO2 partial pressure; Ci, intercellular CO2 partial pressure; Sc, surface area of chloroplasts facing the intercellular air space; Smes, surface area of mesophyll cells facing the intercellular air space; Tr6322-H, transgenic plants of line 6322 with high levels of Aq-anti-HvPIP2;1; Tr6322-L, transgenic plants of line 6322 with low levels of Aq-anti-HvPIP2;1; Tr6360-L, transgenic plants of line 6360 with low levels of Aq-anti-HvPIP2;1.

Journal Article.  6308 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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