INTRODUCTION OF SENSE AND ANTISENSE CDNA FOR BRANCHING ENZYME IN THE AMYLOSE-FREE POTATO MUTANT LEADS TO PHYSICOCHEMICAL CHANGES IN THE STARCH

One isoform of the branching enzyme (BE; EC 2.4.1.18) of potato (Solan um turberosum L.) is known and catalyses the formation of alpha-1,6 bo nds in a glucan chain, resulting in the branched starch component amyl opectin. Constructs containing the antisense- or sense-orientated dist al 1.5-kb part of a cDNA for potato BE were used to transform the amyl ose-free (amf) mutant of potato, the starch of which stains red with i odine. The expression of the endogenous BE gene was inhibited either l argely or fully as judged by the decrease or absence of the BE mRNA an d protein. This resulted in a low percentage of starch granules with a small blue core and large red outer layer. There was no effect on the amylose content, degree of branching or lambda(max) of the iodine-sta ined starch. However, when the physico-chemical properties of the diff erent starch suspensions were assessed, differences were observed, whi ch although small indicated that starch in the transformants was diffe rent from that of the amf mutant.