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Carbohydrate Reserves in Plants - Synthesis and Regulation Ä.K. Gupta and N. Kaur (Editors) © 2000 Elsevier Science B. V. All rights reserved.

Sugar alcohols as carbohydrate reserves in some higher plants

A. Moing

Unité de Physiologie Végétale, Institut National de la Recherche Agronomique Centre de Bordeaux, BP 81, F-33883 Villenave d'Ornon, France

Sugar alcohols are acyclic polyols which play a key role in the metabolism of some higher plants. Three of them are widely distributed in Angiosperms: galactitol, mannitol and sorbitol. Sugar alcohols are primary photosynthetic products which are also involved in response to stress. When a sugar alcohol constitutes a major end-product of photosynthesis in a given species, it is translocated over long distance through the phloem. Sugar alcohols are synthesised outside the chloroplast, via reductases, or reductases and phosphatases. They are degraded via dehydrogenases or oxidases. On a daily time scale, sugar alcohols are temporarily stored in mesophyll tissues. They accumulate in the light and are translocated in the dark. In mature celery leaves, mannitol synthesised in mesophyll cells can be temporarily stored in petiole parenchyma cells, to be remobilised during senescence. On a seasonal time scale, sugar alcohol can be temporarily stored in the perennial parts of some tree species. Conversely, in fruits of species where a sugar alcohol is a major translocated sugar, the main storage form of carbohydrates is starch and hexoses. Several studies suggest that sugar alcohols also play a role in tolerance to low temperature-, drought-, or salt-stress. However, it is not always clear whether this role may be related to osmotic adjustment, accumulation of a compatible solute or the transitory storage of carbon reserves. Sugar alcohols may also play a role in resistance to biotic stress.

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