Distribution of 14C-labeled metabolites in mycorrhizal and nonmycorrhizal lodgepole pine seedlings

Abstract

Four days after 14CO2 assimilation, the distribution of 14C-labeled metabolites in mycorrhizal and nonmycorrhizal pine seedlings was investigated by use of autoradiography, thin-layer chromatography, and liquid scintillation techniques. Mycorrhizal formation was accomplished by growing the lodgepole pine (Pinus contorta Dougl.) seedlings in axenic culture with the fungal symbionts Thelephora terrestris (Ehrh.) Fr., Cenococcum graniforme (Sow.) Ferd. and Winge, and Rhizopogon vinicolor A. H. Smith.Although no significant differences between ectomycorrhizal and uninfected pines were found in the distribution of 14C-labeled metabolites after seedling harvest, important trends were noted in both seedling types with respect to the 14C distribution. Total radioactivity within both mycorrhizal and nonmycorrhizal seedlings was highly correlated with shoot dry weight. Most activity was present in ethanol-soluble fractions. The percentage of activity in ethanol-soluble fractions was greater in roots than shoots. Sugars formed the greatest percentage of the labeled, ethanol-soluble fractions, with sucrose the most common. The roots of all plants analyzed had higher percentages of sucrose and lower percentages of hexoses than did the shoots. Of the hexoses, glucose was more prominent in the shoots and fructose more prominent in the roots of both types of seedlings. Greater quantities of 14C-labeled organic acids and amino acids were found in the shoots than in roots. Both mycorrhizal and nonmycorrhizal plants had similar mean 14C activities in root exudate fractions collected in distilled water. This activity was not correlated with root dry weight or 14C activity within the plant.There was no evidence to support the hypothesis that mycorrhizal development promotes increased translocation of assimilates to the roots or results in increased soluble carbohydrate levels.