This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via CrossRef Citing Articles via Web of Science (9) Citing Articles via Google Scholar Google Scholar Articles by Rosenfield, C.-L. Articles by Loewus, F. A. Search for Related Content PubMed PubMed Citation Articles by Rosenfield, C.-L. Articles by Loewus, F. A. Agricola Articles by Rosenfield, C.-L. Articles by Loewus, F. A.

Articles

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

Department of Biological Sciences, State University of New York, Buffalo, New York 14214

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.

³ Present address: Department of Agricultural Chemistry, Washington State University, Pullman, Washington 99164, to whom requests for reprints and information should be addressed. Scientific Paper No. 4914, Project 0266, College of Agriculture Research Center, Washington State University.

¹ This work was supported in part by Grants GM-12422 and GM-22427 from the National Institute of General Medical Sciences, National Institutes of Health, United States Public Health Service. Taken from a thesis submitted by C-L. Rosenfield in partial fulfillment of requirements for the Ph.D., State University of New York at Buffalo, 1974.

This article has been cited by other articles:

				F. Carrari and A. R. Fernie Metabolic regulation underlying tomato fruit development J. Exp. Bot., June 1, 2006; 57(9): 1883 - 1897. [Abstract] [Full Text] [PDF]