PCP Award: Overexpression of the Barley Aquaporin HvPIP2;1 Increases Internal CO₂ Conductance and CO₂ Assimilation in the Leaves of Transgenic Rice Plants.

Abstract

The internal conductance for CO₂ diffusion (g_i), CO₂ assimilation rate and related anatomical characteristics were investigated in transgenic rice leaves that overexpressed barley aquaporin HvPIP2;1. This study was performed to test that aquaporin facilitates CO₂ 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 aquaporins detected by an antibody raised against HvPIP2;1 (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 CO₂ assimilation rate and a 27% increase in stomatal conductance. In these plants, mesophyll cell size decreased and the cell walls of the epidermis and mesophyll cells thickened, indicating that the leaves were water-stressed.