The aim of this work was to find out how the sugars in the endosperm of oilseed rape contribute to the flux of oil synthesis. While the hexose content of the liquid endosperm decreased during development the sucrose content increased. It is important to understand the relative rates of use of the endosperm sugars for two reasons. Firstly we need to know which sugars are used, and at what stages in development, in order to understand the roles of enzymes involved in their metabolism. Secondly, changes in sugar concentration have been implicated in the regulation of expression of genes determining storage-product synthesis [see Weber, Borisjuk and Wobus (1997) Trends Plant Sci. 2, 169–174, for review]. The rate of consumption of sugar is one factor governing its concentration. We present data showing both the concentration-dependence of conversion of sugar to oil, and the in vivo concentrations of sugars; we relate these data sets to each other and discuss the effects of the intracellular pool of sucrose. Glucose, fructose and sucrose are all substrates for oil synthesis, but the rates of their use (particularly sucrose) are underestimated because of dilution by sucrose from the intracellular pool.

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