Utilization of Storage Sulfur by Cotton and the Effect on Growth and Chloroplast Pigments

Abstract

1. When the sulfate supply to solution cultures of cotton was cut off, the plants used all but 30% of the sulfate S accumulated in the old leaves-in the extension of growth of old tissues and by translocation to new tissues. The 30% residue appeared to be an irreducible minimum. 2. All new leaves became chlorotic soon after initiation, and the chlorosis increased as these leaves expanded and as new ones developed. At the end of a 35-day period without sulfate, some of the new leaves and most of the bolls had abscised, as against no abscission in plants supplied continuously with sulfate. At the same time the old tissues of plants without sulfate increased in dry weight, and the leaves remained green and increased in concentration of chloroplast pigments. 3. There was no decrease in organic S in the old tissues, and evidently none was translocated. Sulfate S was slowly and incompletely available for translocation from old to new leaves but was almost completely drained from roots and stalk. 4. It is concluded that cotton requires a continuous supply of external sulfur for normal growth.