Fructose metabolism in higher plants

Abstract

Fructose 1-phosphate, an important intermediate in the metabolism of fructose in animals and micro-organisms, has only been tentatively identified as a component of higher plant tissues and nothing was known concerning its formation or metabolism in plants. In the present study, examination of tissue extracts from a number ofdifferent plant species by ion-exchange chromatography did not confirmthe presence of endogenous fructose 1-phosphate. However, injectionof fructose into developing Jerusalem artichoke tubers resulted in the rapid formation of labelled glucose 6-phosphate, fructose 6-phosphate, fructose-1,6-bisphosphate, and probably glucose 1-phosphate, followed by the appearance of fructose 1-phosphate which was identified by ion-exchange chromatography and hydrolysis. The incorporation of label into fructosans was also noted and examined.Fructose-l-phosphate was also produced from fructose by tuber calluscultures but not by mature tubers from fructose or by developing 14tubers from sucrose. Attempts to detect a kinase in the developing tubers which would specifically transfer phosphate from nucleotide triphosphates or phosphoenolpyruvate to C-1 of fructose failed although ATP:fructose-6-phosphotransferase activity was identified and partially characterised. Fructose 1-phosphate formation by enzymic isomerization of fructose 6-phosphate or the partial hydrolysis of fructose-1,6-bisphosphate using tuber extracts could not be demonstrated. The major reaction occurring on incubation of fructose 1-phosphate with artichoke tuber extracts appeared to be dephosphorylation.