Cell wall hemicelluloses as mobile carbon stores in non‐reproductive plant tissues

As essential compounds of plant cell walls, hemicelluloses account for about a quarter of all plant biomass worldwide. 2. In seed cotyledons and endosperm of species from several plant families, hemicelluloses are used as mobile carbon reserves. Whether cell wall hemicelluloses of nonreproductive plant tissue are multifunctional molecules, which can also serve as carbon sources during periods of enhanced carbon demand, is still equivocal. 3. This review summarizes the current understanding of a possible reserve function of hemicelluloses. Although several descriptive and experimental studies suggested at least partial mobility of cell wall polysaccharides in mature, non-reproductive plant tissues, there is still a need for a broad-scale, ecophysiological exploration of the actual nature of hemicelluloses beyond their structural function. 4. The chemical heterogeneity of hemicelluloses may be the major problem for precise quantitative analyses on a large, comparative scale. 5. Because of the abundant distribution of hemicelluloses in plants, the existence of a significant mobile carbohydrate pool in cell walls of non-reproductive organs would shed rather new light on plant carbon relations in a source-sink context. 6. Consequently, a reserve function of hemicelluloses questions the conventional division of cell compounds into structural (i.e. immobile) and non-structural (i.e. mobile) compounds.