Aquaporins mediate the movement of water across cell membranes. Plasma membrane intrinsic protein 2;5 from Populus trichocarpa×deltoides (PtdPIP2;5) was previously demonstrated to be a functionally important water conducting aquaporin. To study the relevance of aquaporin-mediated root water transport at low temperatures, we generated transgenic Populus tremula×alba over-expressing PtdPIP2;5 under control of the maize ubiquitin promoter, and compared the physiological responses and water transport properties of the PtdPIP2;5 over-expressing lines (PtdPIP2;5ox) with wild-type plants. We hypothesized that over-expression of PtdPIP2;5 would reduce temperature sensitivity of root water transport and gas exchange. Decreasing root temperatures to 10 and 5°C significantly decreased hydraulic conductivities (Lp) in wild-type plants, but had no significant effect on Lp in PtdPIP2;5ox plants. Recovery of Lp in the transgenic lines returned to 20°C from 5°C was faster than in the wild-type plants. Low root temperature did not induce major changes in transcript levels for other PIPs. When roots were exposed to 5°C in solution culture and shoots were exposed to 20°C, wild-type plants had significantly lower net photosynthetic and transpiration rates compared to PtdPIP2;5ox plants. Taken together, our results demonstrate that over-expression of PtdPIP2;5 in P. tremula×alba was effective in alleviating the effects of low root temperature on Lp and gas exchange.
Keywords: Aquaporin; Hydraulic conductivity; Low root temperature; PIP2;5; Water transport.
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