Consequences of antisense RNA inhibition of starch branching enzyme activity on properties of potato starch

Antisense constructs containing cDNAs for potato starch branching enzyme (SBE) were introduced into potato (Solanum tuberosum L.). A population of transgenic plants were generated in which tuber SEE activity was reduced by between 5 and 98% of control values. No significant differences in amylose content or amylopectin branch length profiles of transgenic tuber starches were observed as a function of tuber SEE activity. Starches obtained from low SEE activity plants showed elevated phosphorous P-31 n.m.r. analysis showed that this was due to proportionate increases in both content. 3- and 6-linked starch phosphates. A consistent alteration in starch gelatinisation properties war; only observed when the level of SEE activity was reduced to below similar to 5% of that of control values. Starches from these low SEE activity plants showed increases of up to 5 degrees C in d.s.c. peak temperature and viscosity onset temperature. Studies on melting of crystallites obtained from linear (1 --> 4)-alpha-D-glucan oligomers suggest that all average difference of double helix length of about one glucose residue might be sufficient to account for the observed differences in gelatinisation properties. We speculate that the modification of gelatinisation properties at low SEE activities is due to a subtle alteration in amylopectin branch patterns resulting in small changes in double helix lengths within granules. (C) 1998 Elsevier Science Ltd. All rights reserved.