Manipulation of S-adenosylmethionine decarboxylase activity in potato tubers An increase in activity leads to an increase in tuber number and a change in tuber size distribution

S-Adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) is a key enzyme in the biosynthesis of the polyamines spermidine and spermine from putrescine and its activity is rate limiting in this pathway. Transgenic potato (Solanum tuberosum L. cv. Desiree) plants containing both sense and antisense SAMDC constructs driven by the tuber-specific patatin promoter have been generated and analysed. In sense transformants, developing tubers expressed higher steady-state levels of the SAMDC-specific transcript, had higher levels of SAMDC activity and contained significantly higher levels of spermidine than vector-transformed controls. Additionally, there was a significant shift in tuber size distribution with larger numbers of smaller tubers but no overall change in tuber yield. In developing tubers from the antisense transformed lines, there was a decrease in SAMDC transcript level, SAMDC activity and total polyamine levels. However, no obvious phenotypic effect was detected in the tuberisation physiology of the antisense lines.