Storage lipids as a source of carbon skeletons for asparagine synthesis in germinating seeds of yellow lupine (Lupinus luteus L.)

The 14C-acetate metabolism and regulatory functions of sucrose and sodium fluoride (NaF) were examined in embryo axes and cotyledons isolated from yellow lupine seeds and grown in vitro. After 15 min of incubating organs in solutions of labeled acetate, more radioactivity was found in amino acids (particularly in glutamate, asparagine and glutamine) than in sugars. After 120 min of incubation, 14C was still localized mainly in amino acids (particularly in asparagine and glutamate). The 14C atoms from position C-1 of acetate were mostly localized in the liberated 14CO2, whereas those from position C-2 were incorporated chiefly into amino acids, sugars and the insoluble fraction of the studied organs. The addition of NaF caused a decrease in the amount of 14C incorporated into amino acids and in the insoluble fraction. The influence of NaF on incorporation of 14C into sugars differed between organs. In embryo axes, NaF inhibited this process, but in cotyledons it stimulated 14C incorporation into glucose. The release of 14CO2 with the C-1 and C-2 carbon atoms from acetate was more intensive in embryo axes and cotyledons grown on a medium without sucrose. This process was markedly limited by NaF, which inhibits glycolysis and gluconeogenesis. Alternative pathways of carbon flow from fatty acids to asparagine are discussed.