Carbohydrate, protein and amino acid status of Glycine‐Glomus‐Bradyrhizobium symbioses

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Abstract
Soybean [Glycine max (L.) Merr. cv. Amsoy 71] plants were inoculated with either the vesicular‐arbuscular mycorrhizal (VAM) fungus Glomus fasciculatum, with a strain of Bradyrhizobium japonicum. or with both endophytes together. Non‐inoculated plants were fertilized with levels of N and P that resulted in plant growth similar to that following infection by Bradyrhizobium or Glomus, respectively. In general, plants colonized by Glomus contained more pinitol (1d‐3‐O‐methyl‐chiro‐inositol) but less starch than corresponding P‐fertilized soybeans, while nodulated soybeans contained more pinitol and sucrose in the roots than corresponding N‐fertilized plants. Compared to nutrient‐amended soybeans, increases or decreases in free amino acids in symbiotically grown plants tended to follow transient changes in N content and endophyte activity. The exception to this was the elevated levels of methionine in nodulated roots or aspartate and arginine in Glomus‐inoculated roots regardless of N level. There were both quantitative and qualitative changes in the proteins found in inoculated soybeans, especially in infected roots where nodulins (nodule‐specific proteins) and endomycorrhizins (mycorrhiza‐specific proteins) were detected by polyacrylamide gel eletrophoresis. Five nodulins (11.8% of root proteins) were detected with molecular weights of 14, 34, 40, 41 and 100 kDa. Five endomycorrhizins (5.1% of root proteins) were detected with molecular weights of 16, 17, 18, 22 and 30 kDa. Differences in nutrient uptake and allocation in symbiotic plants could not be duplicated by fertilizer input alone, although nutrient addition could lead to similar growth rates and dry weight accumulation. These findings suggest that the quality and quantity of plant carbohydrates, proteins and amino acids shift in response to the physiological changes resulting from infection by N2‐fixing bacteria or endomycorrhizal fungi.

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