TRANSLOCATION OF RADIOACTIVE SUGARS IN THE STEMS OF SOYBEAN SEEDLINGS

Abstract

Glucose-C14, fructose-C14, or sucrose-C14 were introduced into soybean seedlings through the cut petiole of one primary leaf. After 3 to 15 minutes the distribution of C14 throughout the plants was determined. Each of the three sugars was translocated as such without conversion to other compounds. Translocation was mainly downward from the point of introduction into the stem. Very little sugar was translocated to the primary leaf opposite the treated petiole or to the growing tip of the stem. Of the small amount of sugar that was translocated upward the bulk accumulated in the younger rather than the older trifoliate leaf.When glucose-C14 or fructose-C14 were used the radioactivity in the stem decreased logarithmically from the point of introduction. The downward translocation of both sugars was impeded at the nodes. Translocation was not inhibited by 10−2 M potassium cyanide. These hexoses were translocated both upward and downward past killed sections of stems. When sucrose-C14 was used the radioactivity in the stem decreased linearly from the point of introduction. Translocation of sucrose was not impeded at the nodes and was inhibited by 10−2 M potassium cyanide. Sucrose was not translocated either upward or downward past killed sections of stems.The minimum rate of translocation of both glucose and sucrose was the same. The rate was about 300 cm. per hour in the youngest seedlings and decreased with age to about 100 cm. per hour in the oldest seedlings.