Mobilisation of storage cell wall polysaccharides in seeds

Plants store carbohydrate polymers in a number of forms. Starch is the principal form, followed by fructans and cell wall storage polysaccharides (CWSP). The latter are present mainly in seeds and consist of magnifications of one of the polysaccharides present in one of the cell wall matrices. CWSPs are classified as mannans, xyloglucans and galactans, the first being subdivided into pure mannans, galactomannans and glucomannans. The present review updates the principal discoveries concerning occurrence, structure, metabolism and eco-physiological significance of the seed storage cell wall polysaccharides with emphasis on their importance for plant metabolism and adaptation to their respective environments during evolution. The properties of CWSPs as storage polysaccharides are compared with starch and fructans and the current knowledge on the catabolism (including control) of mannan/galactomannan, xyloglucan, and galactan is reviewed. On the basis of these data, the idea that the CWSPs are multifunctional molecules is proposed and this feature is used as evidence for the hypothesis that, during evolution, the CWSPs were involved in cycles of transference of functions which led them to become storage polysaccharides, yet preserving some of their previous primary cell wall functions. (C) 2000 Editions scientifiques et medicales Elsevier SAS.