Translocation of manganese, iron, cobalt, and zinc in tomato.
Tomato plants in solution culture were treated with 0 to 50 mum Mn, Co, or Zn in the presence of 5 mum Fe. Stem exudates were analyzed to determine quantities and forms of the metals translocated.Mn had no effect on exudate volume. Co and Zn at 5 mum and above depressed exudate volumes. Nutrient Mn was concentrated 2 to 5 times in the exudates. Co and Zn concentrations were between 1 and 3.Tomato roots treated with 0 to 10 mum Mn released into the exudate an average of 29% of the Fe they absorbed. They released 21% of the absorbed Fe when treated with 50 mum Mn. On 50 mum Co or Zn, the roots released only about 1% of the absorbed Fe.The exudates contained 12 to 47 mum citrate, which was usually considerably in excess of Fe. Electrophoresis of exudate revealed Fe as the only metal in anionic form. Mn, Co, and Zn migrated as cations.The concentration of Ca was >3 mm and Mg >1.5 mm in the exudates. Estimates based on metal-citrate equilibrium constants and constants of metal displacement caused by Ca and Mg confirmed that Mn, Co, and Zn were transported predominantly as inorganic cations in the stem exudates.
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United States Department of Agriculture, ARS, SWC, Mineral Nutrition Laboratory, Beltsville, Maryland 20705.