Down-Regulation of Plasma Intrinsic Protein1 Aquaporin in Poplar Trees Is Detrimental to Recovery from Embolism    

Abstract

During their lifecycles, trees encounter multiple events of water stress that often result in embolism formation and temporal decreases in xylem transport capacity. The restoration of xylem transport capacity requires changes in cell metabolic activity and gene expression. Specifically, in poplar (Populus spp.), the formation of xylem embolisms leads to a clear up-regulation of plasma membrane protein1 (PIP1) aquaporin genes. To determine their role in poplar response to water stress, transgenic Populus tremula 3 Populus alba plants characterized by the strong down-regulation of multiple isoforms belonging to the PIP1 subfamily were used. Transgenic lines showed that they are more vulnerable to embolism, with 50% percent loss of conductance occurring 0.3 MPa earlier than in wild-type plants, and that they also have a reduced capacity to restore xylem conductance during recovery. Transgenic plants also show symptoms of a reduced capacity to control percent loss of conductance through stomatal conductance in response to drought, because they have a much narrower vulnerability safety margin. Finally, a delay in stomatal conductance recovery during the period of stress relief was observed. The presented results suggest that PIP1 genes are involved in the maintenance of xylem transport system capacity, in the promotion of recovery from stress, and in contribution to a plant's control of stomatal conductance under water stress.

Xylem embolism refilling and resilience against drought‐induced mortality in woody plants: processes and trade‐offs

“…Specifically, plasma membrane intrinsic proteins (PIP) are often up-regulated before or during refilling. Secchi and Zwieniecki (2010) reported that Populus trichocarpa showed considerable up-regulation of the PIP1 subfamily of aquaporin water channels, and down-regulation of the same isoform was detrimental to recovery (Secchi and Zwieniecki 2014). In grapevines, two aquaporin genes were activated on stress or refilling, suggesting a specific role in xylem embolism refilling (Chitarra et al 2014).…”

The Role of Plasma Membrane Aquaporins in Regulating the Bundle Sheath-Mesophyll Continuum and Leaf Hydraulics

“…Research in this area has shown that PIP1 and PIP2 antisense lines do not exhibit reduced leaf and plant hydraulic conductivity under normal moisture conditions. However, the lack of functional PIPs results in the significantly slower recovery of plant hydraulic conductivity following exposure to drought (Martre et al, 2002;Secchi and Zwieniecki, 2014). Additional studies have described the Flexas et al, 2007) Data are given as means 6 SE (n, number of independent biological repetitions).…”

Extreme climatic events: impacts of drought and high temperature on physiological processes in agronomically important plants

“…Abscisic acid may accumulate in the roots during the drought period, reach after rehydration the leaves via the xylem, cause stomatal closure and improve as a consequence the water potential in various shoot parts facilitating the repair of embolism (Lovisolo et al, 2008). More recently Secchi and Zwieniecki (2014) reported a strong up-regulation of aquaporin gene expression when xylem embolism was formed. Furthermore, these authors concluded from experiments with transgenic poplar plants that the expression of aquaporin genes is important for the recovery from embolism.…”