Abstract

S3-04

Enzyme Activities of Starch Pathway in Storage Root of Cassava

Daiuto E R¹, L.J.C.B. Carvalho² M.P. Cereda ¹

1.   Faculdade de Ciências Agrônomicas, Universidade Estadual Paulista “Julio de Mesquita Filho”, Botucatu, Brazil

The starch storage capacity of the storage root (SR) of cassava is determined by the sink strength of the secondary xylem-derived parenchyma cells that show a particular pattern of development.  These parenchyma cells originate from the vascular cambium, located in the outermost part of the central cylinder of the SR and increased in maturity to the innermost part of it.  In order to understand the fate of these cells in the accumulation of starch, two cassava cultivars of contrasting rate of starch accumulation were studied using the conceptual compartmentalization tissue model of SR.  Enzyme activities of the starch biosynthesis, sugar and starch content as well as classes of starch granule were evaluated.  Results indicated different patterns of activities depending on the enzyme evaluated.  ADPGase, soluble starch synthase and soluble branching enzyme activities decreased from the outside layers of tissues to the inside layers in the cross section of the SR while debranching enzyme increased but granule-bound starch synthase was not affected.  The sucrose and glucose content decreased from the outside to the inside tissue layers, whereas starch and amylose content increased.  This indicates that amylose accumulated at the later stage in the development of the parenchyma cells of the SR.