Responses of hybrid aspen over-expressing a PIP2;5 aquaporin to low root temperature

Aquaporins mediate the movement of water across cell membranes. Plasma membrane intrinsic protein 2; 5 from Populus trichocarpa x 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 x 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 degrees C significantly decreased hydraulic conductivities (L-p) in wild-type plants, but had no significant effect on L-p in PtdPIP2; 5ox plants. Recovery of L-p in the transgenic lines returned to 20 degrees C from 5 degrees 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 degrees C in solution culture and shoots were exposed to 20 degrees 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 x alba was effective in alleviating the effects of low root temperature on L-p and gas exchange. (C) 2016 Elsevier GmbH. All rights reserved.