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. 1978 Jan;61(1):96–100. doi: 10.1104/pp.61.1.96

Metabolic Studies on Intermediates in the myo-Inositol Oxidation Pathway in Lilium longiflorum Pollen

II. Evidence for the Participation of Uridine Diphosphoxylose and Free Xylose as Intermediates 1

Claire-Lise Rosenfield 1,2, Frank A Loewus 1,3
PMCID: PMC1091804  PMID: 16660246

Abstract

myo-Inositol-linked glucogenesis in germinated lily (Lilium longiflorum Thunb., cv. Ace) pollen was investigated by studying the effects of added l-arabinose or d-xylose on metabolism of myo-[2-3H]inositol and by determining the distribution of radioisotope in pentosyl and hexosyl residues of polysaccharides from pollen labeled with myo-[2-14C]inositol, myo-[2-3H]inositol, l-[5-14C]arabinose, and d-[5R,5S-3H]xylose.

myo-[2-14C]Inositol and l-[5-14C]arabinose produced labeled glucose with similar patterns of distribution of 14C, 35% in C1, and 55% in C6. Arabinosyl units were labeled exclusively in C5. Incorporation of 3H into arabinosyl and xylosyl units in pollen labeled with myo-[2-3H]inositol was repressed when unlabeled l-arabinose was included in the germination medium and a related 3H exchange with water was stimulated. Results are consistent with a process of glucogenesis in which the myo-inositol oxidation pathway furnishes UDP-d-xylose as a key intermediate for conversion to hexose via free d-xylose and the pentose phosphate pathway.

Additional evidence for this process was obtained from pollen labeled with d-[5R,5S-3H]xylose or myo-[2-3H]inositol which produces d-[5R-3H]xylose. Glucosyl units from polysaccharides in the former had 11% of the 3H in C1 and 78% in C6 while glucosyl units in the latter had only 4% in C1 and 78% in C6. Stereochemical considerations involving selective exchange with water of prochiral-R 3H in C1 of fructose-6-P during conversion to glucose provide explanation for observed differences in the metabolism of these 5-labeled xyloses.

Incorporation of 3H from myo-[2-3H]inositol into arabinosyl and xylosyl units of pollen polysaccharides was unaffected by the presence of unlabeled d-xylose in the medium. Exchange of 3H with water was greatly affected, decreasing from a value of 21% exchange in the absence of unlabeled d-xylose to 5% in the presence of 6.7 mm d-xylose.

d-Xylose was rapidly utilized for glucogenesis by germinated pollen tubes. This observation supports the view that free d-xylose is an important intermediate following breakdown of UDP-d-xylose during myo-inositol-linked glucogenesis.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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