Poplar trees for phytoremediation of high levels of nitrate and applications in bioenergy

Abstract

SummaryThe utilization of high amounts of nitrate fertilizers for crop yield leads to nitrate pollution of ground and surface waters. In this study, we report the assimilation and utilization of nitrate luxuriant levels, 20 times more than the highest N fertilizer application in Europe, by transgenic poplars overexpressing a cytosolic glutamine synthetase (GS1). In comparison with the wild-type controls, transgenic plants grown under high N levels exhibited increased biomass (171.6%) and accumulated higher levels of proteins, chlorophylls and total sugars such as glucose, fructose and sucrose. These plants also exhibited greater nitrogen-use efficiency particularly in young leaves, suggesting that they are able to translocate most of the resources to the above-ground part of the plant to produce biomass. The transgenic poplar transcriptome was greatly affected in response to N availability with 1237 genes differentially regulated in high N, while only 632 genes were differentially expressed in untransformed plants. Many of these genes are essential in the adaptation and response against N excess and include those involved in photosynthesis, cell wall formation and phenylpropanoid biosynthesis. Cellulose production in the transgenic plants was fivefold higher than in control plants, indicating that transgenic poplars represent a potential feedstock for applications in bioenergy. In conclusion, our results show that GS transgenic poplars can be used not only for improving growth and biomass production but also as an important resource for potential phytoremediation of nitrate pollution.

Various effects of the expression of the xyloglucanase gene from Penicillium canescens in transgenic aspen under semi-natural conditions

“…For instance, in a similar study of the recombinant GS1 gene expression in poplar hybrids (Populus tremula × P. alba), only eight transgenic lines were analyzed in field trials [17] selected from 22 initially generated transgenic lines that were grown first under greenhouse conditions [16]. Moreover, a detailed study of the recombinant gene was based only on one line [18]. In another similar study of the PIP1 aquaporin gene the initial panel of PIP1-deficient transgenic Populus tremula x alba poplar hybrids included 22 lines, but only six lines were selected for initial tests in the greenhouse [19], and then five of them were selected for the detailed study [20].…”

Influence of Nitrogen Availability on Growth of Two Transgenic Birch Species Carrying the Pine GS1a Gene

“…Overexpression of the GS gene did not change the pigment levels in the leaves of the transgenic plants. Hybrid poplar plants with the GS gene also did not differ in the chlorophyll content from the control at 10 mM nitrogen, whereas at 50 mM levels of chlorophylls a and b significantly increased in the most upper leaves [23]. The chlorophyll content was significantly higher in silver birch plants by approximately 20% (Figure 3) regardless of the nitrogen availability.…”

Overexpression of a pine Dof transcription factor in hybrid poplars: A comparative study in trees growing under controlled and natural conditions

“…Cellulose content was determined by the anthrone colorimetric method [34] with modifications for poplar samples [14]. Lignin levels were determined by the thioacidolysis method [35] and adapted as previously described [36].…”

“…Previous results of our research group have shown that manipulation of the structural and regulatory genes involved in nitrogen metabolism may be a valid approach to increasing biomass production in hybrid poplars ( Populus tremula x P . alba ) and to producing wood with improved pulping attributes [7, 10, 11, 12, 13, 14]. …”