Finnish Forest Research Institute  Metla

Press release 13.01.2006

Lignin modification has no effect on insect herbivores' feeding preferences or growth performance in transgenic silver birch

Chemical modifications of lignin did not seem to have significant impact on insects' feeding preferences on birch leaves nor their relative growth rate under laboratory conditions. Along with cellulose and hemicellulose, lignin is one of the main components of the cell wall in wood.

The chemical structure of lignin in deciduous wood can be modified through transgenic methods. This affects, among other things, the solubility of lignin in chemical pulp manufacturing. So far, possible environmental effects of lignin modified trees have been studied very little. The results of this study, conducted by the Finnish Forest Research Institute Metla and the University of Oulu in collaboration with Prof. Chiang (North Carolina State University, US), concerning transgenic lignin in deciduous trees and feeding experiments with insect herbivores feeding on leaves are among the first in the field. The results are important for environmental assessments regarding transgenic forest trees and moreover, in political decision-making on the role of transgenic forest trees in forest economy based on sustainable development.

In the pulp manufacturing process, lignin is first extracted from wood used as raw material. However, this process is expensive and adds to the environmental burden. In broad-leaved trees the lignin structure comprises mainly syringyl and guaiasyl units and especially the syringyl units improve lignin's solubility. Transgenic methods can be applied to modify the amount and/or chemical quality of lignin. So far, a minimal amount of research has been done on possible environmental effects of transgenic lignin.

In this experiment, the O-methyltransferase gene controlling the formation of the syringyl units was transferred from quaking aspen (Populus tremuloides) into silver birch (Betula pendula Roth). Two of the resulting transgenic birch lines showed a significant reduction in the syringyl/guaiasyl ratio (S/G) compared to non-transgenic control birches. This reduction may slow down lignin's biochemical solubility in, for example, pulping.

Laboratory experiments were performed with insect herbivores to study how chemically modified lignin affects the feeding preferences of lepidopteran larvae (Trichopteryx carpinata, Cleora cinctaria, and Aethalura punctulata) and the adults of birch leaf-feeding beetles (Agelastica alni and Phyllobius spp.) and how it affects the relative growth rate of the lepidopteran larvae. The results indicated that transgenic lignin did not have significant effects on the feeding preferences of the insect herbivores. No differences were found in the growth performance of lepidopteran larvae feeding on transgenic leaves or control leaves.

Publication: Tiimonen Heidi, Aronen Tuija, Laakso Tapio, Saranpää Pekka, Chiang Vincent, Ylioja Tiina, Roininen Heikki, Häggman Hely. Does lignin modification affect feeding preference or growth performance of insect herbivores in transgenic silver birch (Betula pendula Roth) Planta (2005) 222:699-708.

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