COMPLEMENTATION OF THE AMYLOSE-FREE STARCH MUTANT OF POTATO (SOLANUM-TUBEROSUM) BY THE GENE ENCODING GRANULE-BOUND STARCH SYNTHASE

Agrobacterium rhizogenes-mediated introduction of the wild-type allele of the gene encoding granule-bound starch synthase (GBSS) into the amylose-free starch mutant amf of potato leads to restoration of GBSS activity and amylose synthesis, which demonstrates that Amf is the structural gene for GBSS. Amylose was found in columella cells of root tips, in stomatal guard cells, tubers, and pollen, while in the control experiments using only vector DNA. these tissues remained amylose free. This confirms the fact that, in potato. GBSS is the only enzyme responsible for the presence of amylose. accumulating in all starch-containing tissues. Amylose-containing transformants showed no positive correlation between GBSS activity and amylose content, which confirms that the former is not the sole regulating factor in amylose metabolism.