Characterization of starch phosphorylases in barley grains

Starch is synthesized in both leaves and storage tissues of plants. The role of starch syntheses and branching enzymes is well understood; however, the role of starch phosphorylase is not clear.

A gene encoding Pho1 from barley was characterized and starch phosphorylases from both developing and germinating grain were characterized and purified. Two activities were detected: one with a molecular mass of 110 kDa and the other of 95 kDa. It was demonstrated through the use of antisera that the 110 kDa activity was located in the amyloplast and could correspond to the polypeptide encoded by the Pho1 gene cloned. The 95 kDa activity was localized to the cytoplasm, most strongly expressed in germinating grain, and was classified as a Pho2-type sequence. Using RNAi technology to reduce the content of Pho1 in the grain to less than 30% of wild type did not lead to any visible phenotype, and no dramatic alterations in the structure of the starch were observed.

Two starch phosphorylase activities were identified and characterized in barley grains, and shown to be present during starch synthesis. However, their role in starch synthesis still remains to be elucidated.