Sucrose delivers the carbon for cellulose biosynthesis. To make the carbon available, sucrose needs to be enzymatically cleaved. This can be done by two classes of enzymes, sucrose synthases and invertases. Umut Rende from Umeå Plant Science Centre (UPSC) investigated how these two enzyme classes contribute to cellulose biosynthesis in aspen wood. He will defend his PhD thesis at the Swedish University of Agricultural Science on Thursday, the 8th of December 2016.

Invertase TreesControl (WT) and different transgenic aspen lines with reduced invertase activity.Umut Rende has focussed specifically on sucrose synthases and cytosolic neutral invertases, enzymes that are active in developing aspen wood. By analysing transgenic aspen trees with reduced enzyme activity of either sucrose synthases or neutral invertases he could show that neutral invertases are important for cellulose biosynthesis. Sucrose synthase on the other hand is not delivering carbon specifically for synthesis of cellulose but also for other cell wall components like lignin and hemicellulose. 

The transgenic trees Umut Rende and his collegues created grew normally in the greenhouse without any visible differences to non-modified trees. “That was quite disappointing at first,” says Umut Rende. “The total neutral invertase activity in our invertase mutants was reduced by about 50%. We had to look deep into the chemistry and structure of the wood in these trees to see that the cellulose content and the diameter of the cellulose fibrils was reduced. This very specific cellulose defect demonstrated that neutral invertase activity is critical for cellulose formation in developing wood of hybrid aspen.”

The researchers have used Invertase wood anatomyWood anatomy in different invertase aspen mutants (Line 1-3) compared to a control (WT, left side)different approaches to modify the enzyme activity of neutral invertases and sucrose synthases in aspen. The reduction of neutral invertase activity was restricted to developing wood, whereas the activity of sucrose synthase was reduced within the whole plant. Umut Rende and his colleagues showed that in the sucrose synthase mutants the contents of all main woodcomponents - cellulose, lignin and hemicellulose - were lower than in control plants. In these mutants, also the fibre cell wall area and the wood density were reduced indicating a more general role of sucrose synthases.

In parallel to the mutant studies, Umut Rende has together with the Swedish Metabolomics Centre developed a method to quantify sugar phosphates in plant extracts. Sugar phosphates are important intermediates of sugar metabolism in developing wood. “The reliable quantification of these compounds is central for understanding wood metabolism and cell wall biosynthesis”, explains Umut Rende. “We have developed a method to quantify 18 different sugar phosphates in plant extracts that is now ready for use.”

Text: Anne Honsel
Pictures: Umut Rende

Link to the digital publication of the thesis:

For more information, please contact:
Umut Rende
Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences
Phone: +46 (0)18 67 1211
email: This email address is being protected from spambots. You need JavaScript enabled to view it.

Information about the public defence of the dissertation:
On Thursday the 8th of December, Umut Rende, Department of Forest Genetics and Plant Physiology, Umeå Plant Science Centre, Umeå University, will defend his dissertation entitled: "Sucrose cleavage pathways in aspen wood". Faculty opponent will be Professor Samuel Zeeman, ETH Zurich, Switzerland. Supervisor is Totte Niittylä.