Iron-57 accumulation, soybeans

The relative order of efficiency of accumulation of the thpee radionuclides into edible tissues was Zn>Fe>Se. Most of the Zn transported to the above ground plant parts was accumulated by the seeds, however, much of the dose of each of the radionuclides remained in the roots and nutrient solution. The calculated percent of the applied dose taken up by soybean leaves is underestimated since some of the leaves abscised as the plants senesced and they were discarded. Zinc and iron have been classified as partially mobile in the phloem (8). Translocation of iron within plants is poor since new growth of plants require a continuous supply of iron via the xylem or from external applications ( ). Zinc deficiencies of plants can be corrected by applying ZnSO. in a dilute spray. However, iron deficiences of plants are usually difficult to correct which implies a lesser mobility within the plant. 

Little is known about the mobility of selenium in plants. The lesser uptake of selenium may be due to a lower mobility of selenium, to the formation of an insoluble complex between selenite and iron at the acidic pH of the -nutrient solution or to selenium toxicity. The large amount of Se accumulated by the roots of soybeans may reflect a seleniw toxicity. 

The existence of an iron-responsive cis-acting element in plant ferritin genes has been indicated in a series of studies. For example, iron-dependent induction of ferritin synthesis coincided with increased transcription and accumulation of ferritin mRNA [3]. Moreover, insertion of the animal IRE (mRNA iron responsive element) into soybean ferritin mRNA did not have much effect on the translation of the mRNA [4]. In addition, regulation of soybean ferritin expression in nodules [5] appeared to be posttranslational [6]. Finally, no IRE sequence was found in ferritin gene sequences from either maize or soybeans [7]. In fact, the organization of plant... 

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