Overexpression of PIP2;5 Aquaporin Alleviates Effects of Low Root Temperature on Cell Hydraulic Conductivity and Growth in Arabidopsis1[W][OA]

The effects of low root temperature on growth and root cell water transport were compared between wild-type Arabidopsis (Arabidopsis thaliana) and plants overexpressing plasma membrane intrinsic protein 1;4 (PIP1;4) and PIP2;5. Descending root temperature from 25°C to 10°C quickly reduced cell hydraulic conductivity (Lp) in wild-type plants but did not affect Lp in plants overexpressing PIP1;4 and PIP2;5. Similarly, when the roots of wild-type plants were exposed to 10°C for 1 d, Lp was lower compared with 25°C. However, there was no effect of low root temperature on Lp in PIP1;4and PIP2;5-overexpressing plants after 1 d of treatment. When the roots were exposed to 10°C for 5 d, Lp was reduced in wild-type plants and in plants overexpressing PIP1;4, whereas there was still no effect in PIP2;5-overexpressing plants. These results suggest that the gating mechanism in PIP1;4 may be more sensitive to prolonged low temperature compared with PIP2;5. The reduction of Lp at 10°C in roots of wild-type plants was partly restored to the preexposure level by 5 mM Ca(NO3)2 and protein phosphatase inhibitors (75 nM okadaic acid or 1 mM Na3VO4), suggesting that aquaporin phosphorylation/dephosphorylation processes were involved in this response. The temperature sensitivity of cell water transport in roots was reflected by a reduction in shoot and root growth rates in the wild-type and PIP1;4-overexpressing plants exposed to 10°C root temperature for 5 d. However, low root temperature had no effect on growth in plants overexpressing PIP2;5. These results provide strong evidence for a link between growth at low root temperature and aquaporin-mediated root water transport in Arabidopsis.