myo-Inositol Synthesis from [1-H]Glucose in Phaseolus vulgaris L. during Early Stages of Germination

Radiolabeled d-1-³H]glucose was fed by imbibition under sterile conditions to bean (Phaseolus vulgaris L.) seeds. After 72 and 96 hours of feeding, the ³H was located in uronic acid and pentose residues as well as hexose residues of cell wall polysaccharides in growing hypocotyl and root. Free myo-inositol present in cotyledons, hypocotyl, and root also contained ³H, showing that de novo synthesis of myo-inositol from 1-³H]glucose did occur during the first 72 hours of germination. More than 90% of the labeled, free myo-inositol was present in the cotyledons. The ³H percentage in trifluoroacetic acid-soluble arabinose residues of cell wall polysaccharides from 72-hour-old bean hypocotyls was only half of their mole percentage. On the other hand, ³H percentages in hexose residues were higher than their mole percentages. The results suggest that myo-inositol is synthesized from reserve sugars during the very early stages of germination, and that the newly synthesized myo-inositol, as well as that stored in cotyledons, can be used for the construction of new hypocotyl and root cell wall polysaccharides after conversion into uronic acids and pentoses via the myo-inositol oxidation pathway.