Abstract
Transformation of plants with genes encoding a glutamine synthetase (GS), a key nitrogen metabolism enzyme, is usually used to increase productivity. However, overexpression of these genes may increase resistance to phosphinothricin (PPT) that irreversibly inhibits GS causing ammonium accumulation in plant tissues. Transgenic plants of two birch (Betula pubescens) genotypes expressing a pine cytosolic GS gene were used for studying the PPT effect on trees. Two control and 8 transgenic lines were treated with herbicide “Basta” at dose equivalent to 2.5 and 5 Lha−1. Necrosis and abscission of leaves occurred irrespective of a transgenic status or the treatment dose. Ammonium content in leaf tissue in 3 days after the 5 Lha−1 treatment was substantially increased in all plants, 3.2–16.0 times depending on line. After the 2.5 Lha−1 treatment, ammonium content in three transgenic lines was not different from that in control variant sprayed with water. The herbicide treatment caused more prominent desiccation in the bp3f1 genotype nontransgenic plants as compared to transgenic plants, but not in the bp4a genotype. Lack of correlation between ammonium levels and survival of transgenic plants suggests that ammonium toxicity is not a main reason for the birch plant death after the PPT treatment.
Highlights
Increasing productivity of forest plantations is one of the main directions of the genetic engineering of forest trees
To analyze the expression of the GS1 gene before herbicide treatment, RT-PCR was performed with total RNA samples extracted from birch leaf tissue
About 40–60% of leaf area was necrotized in the control and transgenic birch plants in 3 days after the treatment with 2.5 and 5 Lha−1 of the “Basta” herbicide
Summary
Increasing productivity of forest plantations is one of the main directions of the genetic engineering of forest trees. The glutamine synthetase plays a central role in nitrogen metabolism as products of a GS/GOGAT cycle, glutamate and glutamine, are precursors for all the organic nitrogen compounds in plants [2] Though this approach is promising, there are few studies about transfer of the GS gene into woody species; reports for a Populus tremula × P. alba hybrid [3] and for an European aspen (P. tremula) are known [4]. Another problem in forestry is weed control, and herbicide resistant trees could be used to improve productivity and reduce the costs of forest management through to the first and second years after tree establishment [5]. Transgenic plants were treated with different doses of the “Basta” herbicide under open air conditions and resistance level and the foliar ammonium content were measured
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