A further phenotype associated with the reduction of phosphate in the starch is linked to its degradability in different organs of the potato. Initially it was observed that the transgenic potatoes were unable to degrade their starch in leaves even after extremely prolonged (7 days) periods of darkness. The same was later measured in cold-stored potato tubers. The phenomenon of starch degradation and concomittant accumulation of sugars in plant organs induced by low temperatures (cold-induced sweetening) was first described by Mueller-Thurgau, a famous German grapevine breeder, in 1888. Many attempts have been undertaken to circumvent this phenomenon in potato tubers; however, most of them failed. The researchers interpret this observation as a side-effect of the altered starch properties on the starch-degradative machinery present in potato plants. It is hypothesized that the altered starch is not degradable by the enzymes present in potato tubers.

Both of the phenomena observed, the influence on starch phosphorylation and degradation, have a significant impact on plant biotechnology. The high phosphate content of potato starch is an attribute which makes potato starch superior to other commercially available starches. If it was possible to transfer this characteristic to graminaceous and other species, it would open a wide range of novel applications of starch as a renewable resource. In addition, cold sweetening is a severe problem in the potato processing industry as a high sugar content leads to the occurence of the Maillard reaction during frying, which is manifested by the undesired dark staining of potato chips and french fries. Si
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Contact: Jens Kossmann
Kossmann@Mpimp-Golm.MPG.de
+49-331-9772-784
Max-Planck-Gesellschaft
14-May-1998