Interrelationship of Iron and Manganese Supply in Growth, Chlorophyll, and Iron Porphyrin Enzymes in Barley Plants

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Abstract
Barley (Hordeum vulgare var. K 12) plants were raised at 3 levels of Mn, 0.0055 ppm (low), 0.55 ppm (normal) and 5.5 ppm (excess). At each level of Mn, Fe was supplied at 6 levels (0.056, 0.28, 0.56, 1.4, 5.6, and 28 ppm) to give 18 combinations of Fe-Mn supply. Symptoms of Mn toxicity were found to be distinct from Fe deficiency. Excess Fe supply did not produce any visual pathological effects. Yield of plants was determined more by the absolute levels of Fe or Mn supply than by their relative proportions. The Fe/Mn ratio for apparently normal growth and maximum yield of plants varied from 0.25 to 835, depending on the actual levels of Fe and Mn supply. Chlorophyll was depressed by deficiency of Fe and Mn, and by excess of Mn. Fe deficiency and Mn excess depressed catalase. Peroxidase was depressed by Fe deficiency, but often markedly enhanced by Mn excess. Mn deficiency enhanced the effects of Fe deficiency on chlorophyll, catalase, and peroxidase. The effect of variation in Fe and Mn supply on catalase and peroxidase cannot be attributed to the tissue concentration of Fe or to the protein N content of plants, but may be due to a disturbance in the synthesis of specific proteins.