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Effect of a myo-Inositol Antagonist, 2-O, C-Methylene-myo-Inositol, on the Metabolism of myo-Inositol-2-³H and D-Glucose-1-¹⁴C in Lilium longiflorum Pollen ¹

^a Department of Agricultural Chemistry, Washington State University, Pullman, Washington 99164

2-O,C-Methylene-myo-inositol (MMO), a myo-inositol (MI) antagonist, inhibits germination and tube elongation of pollen from Lilium longiflorum cv. Ace or 44. The presence of 5 mM MMO in Dickinson's pentaerythritol medium (Plant Physiol. 43:1-8) partially blocks germination. The tubes produced are short and fail to elongate. In the presence of MI, MMO's toxic effect is blocked. As little as 0.56 mM MI will maintain normal germination in the presence of 43 mM MMO, and pollen tubes continue to elongate for 2 to 3 hr. Eventually, the toxic action of MMO prevents further growth. MMO does not inhibit UDP-D-glucose dehydrogenase from lily pollen.

Uptake of MI-2-³H and incorporation of tritium into galacturonic acid and pentose units of tube wall pectin are blocked by MMO. The site of this inhibition is undertermined. Uptake of D-glucose-1-¹⁴C and incorporation of ¹⁴C into 70% ethyl alcohol-insoluble polysaccharides of germinated pollen are not blocked by MMO, but distribution of label into polysaccharide product is altered. In MMO-treated pollen, very little ¹⁴C is found in uronic acid or pentose units. At 30 mM MMO, about two-thirds of the carbon flow from D-glucose to these pectic components is interrupted. MMO also alters D-glucose metabolism in the 70% ethyl alcohol-soluble fraction, but the compound involved must still be identified.

These results offer fresh evidence of an intermediary role for MI during UDP-D-glucuronate biosynthesis in germinated pollen.

³ To whom inquiries and requests for reprints should be addressed.

¹ Scientific Paper No. 4688, Project 0266, College of Agriculture Research Center, Washington State University, Pullman, Wash. 99164. 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.