Lignin biosynthesis projects concentrate on lignin biosynthesis in developing woody tissue of Norway spruce and Silver birch, both of which are economically important trees in Finland. We have studied especially the last step in lignification, the polymerisation of lignin monomers by peroxidases or laccases. This is of importance as lignin is a compound that gives support to xylem cells (and the whole trees), and on the other hand, has to be removed from wood pulp when white paper is produced.
This topic is studied on the levels of biochemistry, developmental physiology and molecular biology. Methods used include study of enzyme proteins and their corresponding genes by various types of electrophoresis, light and electron microscopy (confocal fluorescence microscopy, SEM and TEM), proteomics, determination of various enzyme activities and compounds by spectrophotometry and nuclear magnetic resonance spectrometry (NMR), and lately by laser microdissection microscope.
The main goals of the project at the moment is to gain detailed knowledge on the function, localisation and expression of xylem-specific peroxidases with special emphasis on their role in lignin biosynthesis in Norway spruce and Silver birch, and on the transport mechanisms of monolignols into the apoplastic space in xylem. Expression of the transcripts of three previously isolated Norway spruce peroxidase genes are followed in differentiating xylem by fluorescence in situ hybridisation using gene-specific molecular probes. Targeting of the protein products of the respective genes has been studied by constructing fusion genes with GFP (green fluorescence protein) and following their transport and processing in transformed tobacco protoplasts. The role of ray parenchymal cells in the prodcution of monolignols is being studied by laser microdissection microscope and transcriptomics to reveal whether monolignol biosynthetic genes are active in the rays.