CBN-V Video Archives - S3-02
Isolation and Biochemical Characterization of High Sugar Storage Root Cassava Clones with Altered Starch Structure

Carvalho L.J.C.B.

EMBRAPA-Genetic Resources and Biotechnology, CP 02372, CEP 70770-900 Sain Parque Rural, Brazilia, Brazil carvalho@cenargen.embrapa.br

        Studies on the regulation and modulation of starch composition and structure in storage organs have traditionally been done based on mutations. Several kinds of mutants on starch biosynthesis have been described in seeds, but none have been found in storage roots of cassava. We are reporting the isolation and the biochemical characterization of two novel clones of cassava with storage root (SR) that accumulates high free sugar, low a-polyglucan, and novel a-polyglucan. The clones were identified in the field by testing with iodine solution and glucose reagent strips. Six out of 22 clones were tested and biochemical characterized. Clones of the series CAS36 accumulate over 100x more free sugar (mainly glucose) than commercial clones. Composition and linkage analysis of water-soluble polysaccharides revealed two sets of isolates with novel sugar composition and linkage type. The structural analysis of the water insoluble polyglucan revealed a novel granular polyglucan, called phytoglycogen, and an amylose free clone. Enzyme activities and protein blot analyses indicated a defective function of the soluble branching enzyme in one of the isolates. A reduced activity of the ADPGase in another clone was also observed. Starch biosynthesis enzyme genes are being isolated by analysis for its expression in those clones.

This research financed by National Biotechnology Program (EMBRAPA), and The Rockefeller Foundation

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