Carbohydrate oxidation by leucoplasts from suspension cultures of soybean (Glycine max L.)

Abstract

The aim of this work was to discover how leucoplasts from suspension cultures of soybean (Glycine max L.) oxidize hexose monophosphates. Leucoplasts were isolated from protoplast lysates on a continuous gradient of Nycodenz with a yield of 28% and an intactness of 80%. Incubation of the leucoplasts with 14C-labelled substrates led to 14CO2 production, that was dependent upon leucoplast intactness, from [U-14C]glucose 6-phosphate, [U-14C]glucose 1-phosphate, [U-14C] fructose 6-phosphate and [U-14C]glucose+ATP, but not from [U-14C]fructose-1,6-bisphosphate or [U-14C]triose phosphate. The yield from [U-14C]glucose 6-phosphate was at least four times greater than that from any of the other substrates. When [1-14C]-, [2-14C]-, [3,4-14C]-, and [6-14C]glucose 6-phosphate were supplied to leucoplasts significant 14CO2 production that was dependent upon leucoplast intactness was found only for [1-14C]glucose 6-phosphate. It is argued that soybean cell leucoplasts oxidize glucose 6-phosphate via the oxidative pentose phosphate pathway with very little recycling, and that in these plastids glycolysis to acetyl CoA is negligible.