MICROBIAL FRUCTAN PRODUCTION IN TRANSGENIC POTATO PLANTS AND TUBERS

Fructans (fructose polymers) derived from plants usually have a very l ow degree of polymerisation (DP) and this limits the technical applica tion of this versatile carbohydrate polymer. Previously we showed that the expression of bacterial fructosyltransferase genes in transgenic plants results in the accumulation of high molecular weight fructans w ith a DP of over 25,000. Here we report on our progress in accumulatin g such high DP fructans in potato plants and tubers. In these plants g rowth, tuber formation and carbohydrate partitioning were analyzed. Yo ung plants showed no difference in growth between wildtype and fructan -producing (KP) plants. However, at a certain timepoint growth in KP p lants is reduced and photosynthate starts to accumulate in source leav es. In these plants no diurnal turnover of starch and sucrose is obser ved. At harvest, the sink organs (roots, tubers) are reduced in weight . Depending on fructan content the KP tubers display a brown phenotype and yield was reduced. The starch content in the KP tubers is inverse ly correlated with the fructan level, whereas the sucrose, glucose, fr uctose and protein levels increase substantially, concomitant with fru ctan concentration. The cellular location of the fructans was investig ated via immunofluorescence using monoclonal antibodies against levan and this showed the presence of fructan located along the cell rim ins tead of in the expected vacuolar location. It is concluded that fructa n accumulation in these plants dramatically affects growth and carbohy drate partitioning and possible solutions for these problems are discu ssed.