The molecular structure of leaf starch from three cereal crops

Abstract

Plants produce storage and transient starches in seeds and in leaves, respectively. Understanding molecular fine structure and synthesis of transient starch can help improve plant quality (e.g. by helping breeders produce slowly digested amylopectin, which is beneficial for human nutrition). In the present study, leaf starches from rice, wheat and barley were isolated with cesium chloride gradient centrifugation. Starch fine structure was measured using size-exclusion chromatography and flurophore-assisted carbohydrate electrophoresis. The chain-length distribution (CLD) of amylopectin leaf starch was trimodal in wheat and barley leaf starch. The global peak of leaf starch was at degree of polymerization (DP) 22, and leaf amylopectin containeds more long branches, which are generally considered to hinder starch digestion, suggesting that leaf-specific starch synthesis enzymes could be expressed in the endosperm by genetic modification to produce amylopectin with more long chains, which would be more slowly digested, with advantages to human health. The biosynthetic processes for leaf starch and storage starch in a given plant species will show significant differences. • Rice, wheat and barley leaf starches were isolated by CsCl gradient centrifugation • Leaf-starch whole molecular sizes were smaller than those in storage starch • Amylopectin from leaf starch contained more long chains than from the endosperm starch • Leaf and storage amylopectin had trimodal and bimodal chain-length distributions. • This indicates significant differences in biosyntheses of leaf and storage starches

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