The mechanism of de novo synthesis of fructooligosaccharides in leaf disks of certain Asteraceae. III.

Abstract

14C-tracer experiments revealed that both endogenous and exogenous substrate was incorporated in the fructosans synthesized in leaf disks during incubation on phosphate-buffered sugar media. At least some of the endogenous substrate was derived from a source which was insoluble in 80% ethanol at the start of the incubation period. Endogenous and exogenous substrates were distributed in the fructosans in a pattern which was qualitatively similar regardless of the type of sugar supplied exogenously. A complex relationship was exhibited between the specific activity of various fructosan oligomers, expressed on a gram basis, and their chain length. However, expressed on a molar basis, the specific activity of the fructosyl tail portion of each homolog appeared to be linearly related to the number of hexosyl residues that it contained. Such a relationship suggests that enzymes similar to the Jerusalem artichoke tuber transfructosylases are present in leaf disk tissue after 72 h incubation and indeed may function in the de novo synthesis of fructosans in vivo.