CARBOHYDRATE OXIDATION BY LEUKOPLASTIDS FROM SUSPENSION-CULTURES OF SOYBEAN (GLYCINE-MAX L)

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 C-14-labelled substrates led to (CO2)-C-14 production, that was dependent upon leucoplast intactness, from [U-C-14]glucose 6-phosphate, [U-C-14]glucose 1-phosphate, [U-C-14] fructose 6-phosphate and [U-C-14]glucose + ATP, but not from [U-C-14]fructose-1,6-bisphosphate or [U-C-14]triose phosphate. The yield from [U-C-14]glucose 6-phosphate was at least four times greater than that from any of the other substrates. When [1-C-14]-, [2-C-14]-, [3,4-C-14]-, and [6-C-14]glucose 6-phosphate were supplied to leucoplasts significant (CO2)-C-14 production that was dependent upon leucoplast intactness was found only for [1-C-14]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.