Influence of Sulphur Deficiency on the Metabolism of the Soy Bean

Abstract

1. The effects of sulphur deficiency were studied in the soy bean. It took considerable time for symptoms of sulphur deficiency to become apparent, but they were beginning to show in four weeks' time and had become pronounced in six weeks. 2. The main symptoms were the yellow-green color of the leaves, the smaller leaflets, and the thinner stems. These symptoms are similar to those that have been noted for other elements, for example, nitrogen, potassium, and phosphorus. This no doubt indicates a similar cause, namely, poor nitrate assimilation. 3. The upper leaves become yellow first. This is similar to the effect of sulphur deficiency in the tea bush and to calcium deficiency in the tomato, but is in contrast to deficiency of nitrogen, potassium, or sulphur in the latter plant. In the case of the latter elements, the lower leaves become yellow first. 4. Stem elongation was a prominent feature of both plus and minus sulphur plants because of the use of electric lights for part of the light period. Omitting sulphur from the nutrient solution caused some reduction in the height of the plants, but still the stems elongated remarkably. This is in contrast to the deficiency of other elements and is no doubt correlated with the ability of these plants to break down and reutilize proteins. 5. Sulphur deficiency affected the tops of the plants more than the roots. This is similar to the effects of nitrogen deficiency and also to some of the results reported for phosphorus deficient plants. 6. The stems of the minus sulphur plants were harder than those of the plus sulphur plants. Cell wall thickness has been found correlated with an accumulation of carbohydrates. In the case of the soy bean, it seems more correlated with the accumulation of starch and hemicelluloses than with all forms of carbohydrates. 7. Characteristic symptoms of boron deficiency appeared in a number of the plants grown in 1933. The numbers of plus sulphur and minus sulphur plants showing this injury were about equal. The addition of boron caused the quick formation of side shoots. It is not thought that boron deficiency affected the differences in the plus and minus sulphur plants. 8. The plus sulphur plants were more succulent than the sulphur deficient plants. In this they were like plants grown with plenty of nitrates in the nutrient solution. 9. Nitrates accumulated in the minus sulphur plants. This was because of poor nitrate assimilation. Deficiency of other elements may also cause this. It would be expected that in such circumstances carbohydrates would also accumulate. Starch and hemicelluloses were higher in the sulphur deficient plants, but sugars accumulated in the plus sulphur plants. Sulphur deficiency apparently affects the form of carbohydrate accumulation in the soy bean. This is in contrast to the tomato, in which all forms of carbohydrates accumulate in the minus sulphur plants. 10. There is some evidence that hemicelluloses serve as reserve food materials in the soy bean. 11. The soluble organic nitrogenous fractions were higher in the minus sulphur plants, especially in the stems. This was at least partly due to proteolysis, and is important in accounting for the stem elongation of the minus sulphur plants. When proteolysis occurs, there is usually also a decrease in carbohydrates. The sulphur deficient plants were higher in starch and hemicelluloses but lower in sugars; therefore the proteolysis which occurs is of a special type. But since the minus sulphur plants are lower in sugars, these plants may perhaps be regarded as more in accord with the usual situation accompanying proteolysis than sulphur deficient tomato plants, in which all forms of carbohydrates accumulate. 12. Accumulation of the soluble organic nitrogenous fractions in the minus sulphur plants no doubt was partly due to the new synthesis of these compounds and the failure of the completion of protein synthesis because of the lack of sulphates, for nitrate reduction may no doubt go on slowly in sulphur deficient plants. This may have a bearing in explaining the somewhat abnormal situation in regard to the accumulation of carbohydrates during proteolysis. 13. Similar symptoms of sulphur deficiency were noted in the sunflower, kale, rape, and mustard. The influence of sulphur deficiency in reducing the mustard oil content was definitely evident in the mustard. The leaves of the minus sulphur plants were not nearly so acrid in taste as those of the plus sulphur plants.