De novo synthesis of fructooligosaccharides in leaf disks of certain Asteraceae. II. Certain physiological and biochemical changes accompanying fructooligosaccharide formation

Abstract

De novo synthesis of fructosans in leaf disks of certain Asteraceae incubated on phosphate-buffered 5% sucrose medium was accompanied by increases in fresh and dry weight and a considerable enhancement in the rate of respiration. Radiorespirometry using 14C-sucrose showed that the respiratory pool was kept at the expense of both exogenous and endogenous substrates. During the initial 24 h of incubation, about 80% or more of the total respiratory carbon was derived from the exogenously supplied sugar. This proportion gradually decreased during the last 48 h to a final value of about 50%. Of the total sugar taken up by the leaf disks, less than 20% was utilized in respiration while more than four-fifths was available for further metabolism including fructosan formation. The respiratory quotient values remained relatively unchanged from 0.8 to 0.9 throughout most of the incubation period and suggested that endogenous substrate other than carbohydrate was drawn into respiratory metabolism.