Effects of Phosphorus Deficiency on Growth and Metabolism of Black Mustard. Contributions from the Hull Botanical Laboratory 631

Abstract

1. Sand cultures were used in a study of the effects of phosphorus deficiency on black-mustard plants (Brassica nigra [L.] Koch). The first symptom observed was the deeper-green color of the leaves. Neither chlorosis nor anthocyanin development was prominent, although some of the lower leaves became chlorotic, and a few plants developed a small amount of anthocyanin in the hypocotyls and stems. The deficient plants were short with small leaves and thin stems. No difference in hardness of the stems of the two groups was apparent. Top growth was limited more than root growth, so that the top-root fresh-weight ratio of minus-phosphorus was lower than that of plus-phosphorus plants. 2. Phosphorus-deficient stems were slightly lower in moisture than those on complete nutrient. The former stems were high in total sugars, reducing sugars, and sucrose but contained about the same amount of starch as the latter stems. The accumulation of sugars is interpreted as being a consequence of the greater leaf-stem fresh-weight ratio of the minus-phosphorus as compared with the plus-phosphorus plants. A small part of the accumulation seemed to be due to a slight disturbance of protein synthesis at the amide stage. 3. Phosphorus deficiency did not seriously disturb the nitrogen metabolism of black-mustard stems. There was a slight accumulation of amides in the minus-phosphorus stems; total nitrogen, soluble nitrogen, and nitrates were higher in the plus-phosphorus ones. The concentration of ammonia was about the same in stems of the two sets. 4. Total phosphorus, soluble phosphorus, and insoluble phosphorus were much higher in plus-phosphorus than in phosphorus-deficient stems. The soluble phosphorus made up a much larger percentage of the total phosphorus in the latter than in the former stems. 5. The effects of phosphorus deficiency on plants in general are discussed with especial emphasis on a comparison of the three species of this project.