METABOLISM OF GLUCOSE MONOPHOSPHATES BY LEUKOPLASTIDS AND AMYLOPLASTSFROM SOYBEAN SUSPENSION-CULTURES

Leucoplasts and amyloplasts were isolated on Nycodenz gradients from l ysates of protoplasts of suspension cultures of soybean (Glycine max). The labelling of CO2 and starch was determined after incubating intac t and lysed preparations of plastids with C-14-labelled substrates. Th e substrates were said to have been metabolized by the plastids if the labelling of the product was greater in the intact than in the lysed preparations. Leucoplasts and amyloplasts metabolized both [C-14]gluco se 1-phosphate and [C-14]glucose 6-phosphate to (CO2)-C-14. In both ty pes of plastid [C-14]glucose 6-phosphate was the better precursor. Nei ther substrate was converted to starch by intact leucoplasts. Amylopla sts converted [C-14]glucose 1-phosphate, but not [C-14]glucose 6-phosp hate, to starch in the presence of exogeneous ATP. It is suggested tha t in these plastids the reaction catalysed by phosphoglucomutase is no t at equilibrium.