| Abstract: | Potato microtubers (cv Maris Piper) were grown at 10, 16 and 24°C in total darkness for 28 days. Soluble and insoluble starch synthase, ADPglucose pyrophosphorylase, sucrose synthase and fructokinase were assayed in extracts of the microtubers and, in the case of soluble and insoluble starch synthase, activity was found to be particularly sensitive to increasing growth temperature. The starch content of the microtubers increased slightly with increasing growth temperature, but with little effect on the number of granules per microtuber and a small increase in the average granule size. The microtuber starch granules were much smaller than those found in commercial potato starch (c 8–9 μm modal diameter compared to c 21 μm). Although the amylose content of the microtuber starches tended to increase with increasing growth temperature, the phosphorus content was variable. Gel permeation chromatographic elution profiles of native and debranched microtuber and a commercial potato starch showed that no differences could be detected in either amylose or amylopectin molecular size, polydispersity or unit chain distribution of amylopectin (which contained two major unit chain fractions at DP 21 and 56). The onset, peak and conclusion temperatures of the DSC gelatinisation endotherm increased linearly as a function of growth temperature whilst the enthalpy of gelatinisation decreased. It is suggested that elevated temperature during starch biosynthesis facilitates ordering of amylopectin double helices into crystalline domains. © 1998 SCI. |
