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

Abstract

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/zmol L-~, 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.

Enrichment of some B-vitamins in plants with application of organic fertilizers

“…(Radioisotope Dilution, also called protein binding) method using the test kit CT.302 supplied by Amersham of England as described elsewhere (Mozafar and Oertli, 1992a). Vitamin B12 measured by the RID method using purified hog intrinsic factor shows close correlation with the results obtained by the Euglena test (Bennink and Ono, 1982;Casey et al, 1982;Oesterdahl et al, 1986;Richardson et al, 1978;Stenman and Puutula-R~is~en, 1980).…”

“…These data are in contrast to the views that plants do not contain B12 at all and that the B12 activity found in plants (Robbins et al, 1950) seems to be due to contamination of plants with soil bacteria (Chanarin, 1969;Gr/isbeck and Salonen, 1976). Considering the reports that plant roots and leaves can absorb the relatively large molecules of Bl2 from nutrient solutions and transport them to other plant parts (Mozafar and Oertli, 1992a) and the belief that plants cannot synthesize this vitamin (Friedrich, 1987;Lehninger, 1977;Smith, 1960), it seems that the observed increase in the concentration of B12 in barley seeds and spinach leaves fertilized with cow dung is mostly (if not fully) due to the uptake of this vitamin by the roots from the soil and not due to superficial contamination or an increased synthesis of this vitamin within the plant.…”

Possible Roles of Rhizospheric and Endophytic Microbes to Provide a Safe and Affordable Means of Crop Biofortification

“…Barley and spinach treated with pure vitamin B 12 or cow dung showed increased vitamin B 12 levels in the seeds and leaves, respectively [112]. The uptake of vitamin B 12 by soybean roots in a vitamin B 12 -supplemented nutrient solution was also reported [119]. As early as the 1950s, it was found that the vitamin B 12 content in turnip greens was geography-dependent [120].…”

Acquisition of phosphorus and nitrogen in the rhizosphere and plant growth promotion by microorganisms

“…thiamine, biotin, riboflavine, niacin) has been documented in some Azospirillum, Azotobacter, Pseudomonas fluorescens and Rhizobium strains (Marek-Kozaczuk and Skorupska 2001;Revillas et al 2000;Rodelas et al 1993;Sierra et al 1999). There is evidence that exogenous supply of B-group vitamins to plants favours root development (Mozafar and Oertli 1992), but there is presently no direct evidence (e.g. using mutants) that PGPR can stimulate plant growth through this mechanism (Marek-Kozaczuk and Skorupska 2001), although further work is warranted.…”