Influence of Mineral Elements Upon Development of Chloroplast Pigments of Soy Beans

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1. Soy bean plants were grown in nutrient solutions in which the concentrations of the iron, potassium, and sulphur contents were varied. 2. Ferric citrate was found to be four to thirteen times more efficient an iron source than ferrous sulphate. This difference in efficiency was constant in a given experiment. 3. Small differences in the iron content of the nutrient solutions produced considerable differences in the growth of the plants. 4. Iron deficiency caused small black spots to develop in the chlorotic new leaves. 5. Lack of potassium stunted growth markedly, but concentrations of 28-238 p.p.m. of this element produced about the same amount of growth. 6. The sulphur content of the nutrient solution influenced growth only slightly. 7. Acetone extracts of the total pigments of leaves are not safe criteria for judging the relative chloroplast pigment development. 8. Ether extracts of the chloroplast pigments freed from water soluble pigments are more satisfactory for judging the relative chloroplast pigment content than acetone extracts. 9. The separated carotinoid pigments may show greenish tinges which interfere with their quantitative estimation. 10. Estimation colorimetrically of chlorophyll (a and b) against a standard of purified chlorophyll (a and b) in alcohol was found to be a very satisfactory method. 11. The lack of iron or potassium in the nutrient solution resulted in a more marked depression of the chloroplast pigments than a lack of sulphur. 12. In general, the chloroplast pigments increased with the increasing concentrations of iron and sulphur. The highest concentration of sulphur used (46 p.p.m.) caused a marked decrease in the pigment content of the leaves. 13. Concentrations of potassium above 28 p.p.m. reduced the chloroplast pigments when the extractions were made from fresh leaves. 14. In all the experiments the chlorophylls (a and b) and carotinoids were influenced by the composition of the nutrient solution to about the same extent. 15. An exact proportional relation could not be established between the concentration or amount of any of the elements studied and the amount of pigment formed. 16. A correlation between the green weight of the plants and the chlorophyll (a and b) existed in one experiment with iron, but did not apply in the other experiments.