A metabolic survey on aspen developing wood employing isotopic labelling

DOMINGUEZ PG

Guangzhou

Simposio; International Workshop of Plant Cell Wall Study; 2018

South China Agricultural University (SCAU)

The reactions composing central metabolism establish a ubiquitous network that controls most of the flow of carbon into the cells. Thus, we have aimed to study the central metabolism during the transition from primary to secondary cell wall formation to shed light into the differences in the incorporation of carbon by the different tissues comprising wood. We took advantage of the developmental gradient of the cell wall in aspen developing wood that ranges from the expansion zone (with only primary cell walls), the secondary cell wall formation zone and to the maturation zone (characterised by the presence of secondary cell walls and cell death). We studied the flow of carbon into these tissues by means of isotopic labelling experiments. We provided the plants with 13CO2 in a special chamber and analysed the 13C-labelled metabolites over time. In order to know the different labelling patterns of the central metabolites we performed a K-means analysis. The metabolites belonging to the core of the central metabolism (sugars and TCA cycle metabolites) showed a very similar labelling pattern in the different tissues comprising wood. This suggests that the differences in the regulation of the reactions in which these metabolites are involved are possibly small. The metabolites that are peripheral in the central metabolism (like amino acids) show differential clustering according to the different tissues, suggesting that they either participate in different reactions or are regulated differently. Shikimate, for example, which is known as an early precursor of lignins, is less labelled in the expansion zone in comparison with the zones where there are secondary cell walls, suggesting that the flow of carbon through this metabolite is increased when lignins start to be produced.When sucrose enters the wood cells, it is metabolised either by an invertase or by the sucrose synthase (SUS). A previous work in the group (Gerber et al., 2014) suggested that SUS could be involved in controlling the flow of carbon into aspen wood cells. Thus, we assessed the flow of carbon in the SUS transgenic lines at the whole tree level using 13CO2. Indeed, the percentage of enrichment of sucrose was reduced in the leaves, phloem and developing wood of the SUS trees in comparison to the wild-type trees, indicating an alteration in the sucrose transport and metabolism at the whole plant level. In developing wood, the total levels of soluble sugars were not altered, maybe due to the increased activity levels of the acid invertase. The SUS trees did not show any differences at the biomass levels when grown in the greenhouse in spite of having reduced total carbon levels. However, when the SUS lines were assessed in the field, the wood biomass was significantly reduced. This result shows that SUS is an important biomass determinant in aspen wood.