Uptake of a microbially-produced vitamin (B12) by soybean roots

Vitamin B12 (Cyanocobalamin) is one of the vitamins believed to be produced exclusively by microorganisms. Although soil is a rich source of vitamin B12, systematic study as to possible uptake of this vitamin by the plant roots is lacking. This study was undertaken to investigate, under water culture conditions, the uptake of ⁵⁷Co]-cyanocobalamin by soybean (Glycine max (L.) Merr.). In the range of 10 to 3200 mol L^–1, uptake of vitamin B12 was a linear function of the vitamin concentration in the nutrient solution. Depending on the vitamin concentration, 12 to 34% of the total absorbed vitamin was transported to the plant shoots, with proportionally more vitamin B12 transported at higher vitamin concentrations. Aeration of the rooting medium with nitrogen gas significantly increased the total uptake and the percentage of vitamin transported to the shoots. Addition of respiration inhibitor dinitrophenol to the nutrient solution did not affect the total uptake or the partitioning of the vitamin. Root temperature (5–30°C) did not affect the total uptake but significantly altered the partitioning of the vitamin between the roots and the shoots. Foliar-applied vitamin B12 was not translocated to any considerable degree to other plant parts, indicating that phloem transport does not contribute to the distribution of this vitamin within the plant. It is suggested that adding manure (which is rich in this vitamin) to the soil could increase soil and thus plant content of vitamin B12. This could be of importance in raising the intake of this vitamin by people living by choice or necessity on vegetarian diets who are usually threatened by vitamin B12 deficiency.