Plant Physiol. Journal of Pharmacology and Experimental Therapeutics
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Plant Physiology 43:979-989 (1968)
© 1968 American Society of Plant Biologists

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Inositol Metabolism in Plants. V. Conversion of Myo-inositol to Uronic Acid and Pentose Units of Acidic Polysaccharides in Root-tips of Zea mays 1

R. M. Roberts, J. Deshusses2 and F. Loewus

Department of Biology, State University of New York, Buffalo, New York 14214

The metabolism of myo-inositol-2-14C, D-glucuronate-1-14C, D-glucuronate-6-14C, and L-methionine-methyl-14C to cell wall polysaccharides was investigated in excised root-tips of 3 day old Zea mays seedlings. From myo-inositol, about one-half of incorporated label was recovered in ethanol insoluble residues. Of this label, about 90% was solubilized by treatment, first with a preparation of pectinase-EDTA, then with dilute hydrochloric acid. The only labeled constituents in these hydrolyzates were D-galacturonic acid, D-glucuronic acid, 4-O-methyl-D-glucuronic acid, D-xylose, and L-arabinose, or larger oligosaccharide fragments containing these units. Medium external to excised root-tips grown under sterile conditions in myo-inositol-2-14C contained labeled polysaccharide.

When label was supplied in the form of D-glucuronate, the pattern of labeled uronic acid and pentose units in cell wall polysaccharides resembled that obtained from labeled myo-inositol, indicating that both substances were metabolized along a common path during polysaccharide formation, and that methylation occurred at a step subsequent to uronic acid formation. When label was supplied in the form of L-methionine-methyl-14C, 4-O-methyl-D-glucuronic acid was the only labeled monosaccharide component that survived enzymatic or acid hydrolysis.

Zea mays endosperm, a known source of phytin, developed maximal phytase activity after the third day of germination. Results obtained here suggest that myo-inositol released by hydrolysis of phytin represents the initial precursor of a normal, possibly predominant pathway for the formation of uronic acids in plants.

2 Permanent address: School of Chemistry, University of Geneva, Geneva, Switzerland.

1 Supported by grant (GM-12422) of the NIH, United States Public Health Service.






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Copyright © 1968 by the American Society of Plant Biologists