Occurrence metabolism transport and function of

Authors: A Keith Cowan

Publish Date: 2016/03/28

Volume: 16, Issue: 1, Pages: 137-157

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Abstract

Sevencarbon 7C sugars and sugar alcohols are common in higher plants algae fungi and bacteria The biochemical origin and physiological function of these monosaccharides in plants and algae however is not well understood and has not been fully investigated Here the occurrence metabolism and transport of heptuloses heptitols and heptoses are integrated in accordance with function to emphasise the importance of these apparently neglected sugars This therefore is the first comprehensive synthesis of knowledge about 7C sugar biochemistry a relatively underexplored area of carbohydrate biology that needs to be integrated into mainstream sugar research Available information on the metabolism of heptuloses heptitols and heptoses in Medicago sativa alfalfa Persea americana avocado Primula sp Kalanchoë pinnata and the red alga Porphyridium sp was thoroughly investigated and evaluated Results indicate that 7C sugars share a common precursor and are products of a TKTdependent heptulose shunt in which Sucderived Fru 6P is converted either to Sed 7P or mannoheptulose 7P or both in competent tissues and species In plants free heptuloses probably arise as a consequence of phosphatase activity whereas heptoses appear to be formed by isomerisation of the corresponding phloem translocated heptuloses following import into nonphotosynthetic tissue It is proposed that the major physiological function of 7C sugars and heptitols in addition to serving as a carbon sink involves metal ion chelation translocation and remobilisation to fulfil nutrient requirements essential for growth and development

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