Poster: Membrane Transport

Abs # 1197: Increase in leaf CO₂ conductance and decrease in salt tolerance in transgenic rice plant over-expressing barley aquaporin

Presenter:	Katsuhara, Maki , kmaki@rib.okayama-u.ac.jp
Authors	Katsuhara, Maki  (A)   Hanba, Yuko  (A)   Koshio, Kazuki  (A)   Shibasaka, Mineo  (A)   Hayashi, Yasuyuki  (B)   Hayakawa, Takahiko  (B)   Kasamo, Kunihiro  (A)
Affiliations:	(A): Research Institute for Bioresources, Okayama University (B): Plantech Research Institute
Web Site:	http://www.rib.okayama-u.ac.jp/~kmaki/katu_e.html

Aquaporins are membrane proteins forming water channels. Human aquaporin AQP1 is permeable for gas CO₂ in addition to H₂O. In Characean cells and Vicea leaflets, physiological experiments indicated the correlation between water permeability and CO₂ permeability in the plasma membrane.
In the present study, we measured the CO₂ permeability (diffusion conductance, g_i) in leaves of transgenic rice plants over-expressing a barley aquaporin (HvPIP2;1, ref 1). Expressions of introduced gene and protein were confirmed with Southern, Northern, and Western analysis in T₀ plants, and descendent T₂ leaves were subjected to g_i measurement. Transgenic plants showed slight higher assimilation than non-transgenic wild type plants. Higher g_i was observed in higher HvPIP2;1-expressing individuals. In average, about 20% increase in g_i was found in transgenic leaves. This result is the first molecular evidence that plant aquaporin permeates CO₂.
Under control condition, high root hydraulic water conductivity and high mass ratio of shoot/root were observed in transgenic T₂ plants. When salt stress of 100 mM NaCl was applied to the hydroponic culture, reduced growth but not lethal effect was observed in wild type rice plants. In transgenic T₂ plants under same stress condition, however, severe damage was observed and T₂ individuals withered to die. It will be discussed that transgenic plants over-expressing aquaporin can not regulate the root water permeability and decreased in salt tolerance because of water loss from the tissue.
(1) Katsuhara et al. Plant Cell Physiol. 43:885-893 (2002)