Single leaves of tobacco plants at four different stages of development were allowed to carry on photosynthesis in C14O2 for 30 to 50 minutes followed by photosynthesis in air. The total elapsed time from the beginning of assimilation was [Formula: see text] hours. Redistribution of C14 was determined in: I, a young plant with eight leaves; II, an older plant with 19 leaves; III, a mature flowering plant with 29 leaves; IV, a mature seed plant with 35 leaves. The leaf treated with C14O2 in each of the four plants was number seven, counting from the bottom. This leaf was only half expanded in the youngest plant but fully expanded in the other three plants.The treated leaf of the youngest plant translocated 22% of the total C14 fixed, twice as much as the treated leaves of the other three plants. The large amount of translocation in the youngest plant occurred from a leaf that contained 28% of its ethanol-soluble fraction as sugar phosphates and only 25% as sucrose. The treated leaves of the older plants that translocated half as much radioactivity had less C14 in sugar phosphates and more C14 in sucrose. For example, the treated leaf of the seed plant contained 13% of its soluble C14 in sugar phosphates and 70% in sucrose.Sucrose and some hexose was recovered from the stems and roots of all plants. Amino acids were recovered from both stem and root of the youngest plant but not from these parts of the three older plants. Since 80 to 100% of the C14 in the stems was recovered as sucrose it is concluded that this sugar is the main form in which carbon is translocated in tobacco. Although sugar phosphates and organic acids were found in the treated leaves of all plants they were not detected in stems or roots and were apparently not translocated.All plants translocated C14 to leaves both below and above the treated leaf. Two factors influenced the destination of C14. One was the anatomical connection among leaves, and the second was the stage of development of any particular leaf. Although C14 was translocated to leaves at nodes bearing flowers no C14 was translocated to these flowers or to developing or mature seeds in any of these plants.

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Abstract. When single leaves attached at a given node were allowed to carry on photosynthesis in 14CO2 for 30 min, younger plants showed a higher proportion of upward translocation than did older plants. Downward translocation of 14C-photosynthate was stimulated by ATP pre-treatment of the translocating leaf, while upward translocation was not affected by ATP. A similar phenomenon was observed in the translocation of 14C-sucrose infiltrated into a leaf with or without ATP. Downward translocation of photosynthate was inhibited by DNP pre-treatment of a fed leaf. Upward translocation, however, was not affected by DNP. Thirty min after infiltration of 14C-glucose into a leaf, almost all the 14C translocated upwards was found to be in the form of glucose, whi'le a great part of the 14C translocated downwards was in the form of sucrose. In the case of translocation of infiltrated 14C-suerose, 14C found both above and below the fed leaf was mainly in the form of sucrose.In our previous study (7) 2) whether the mechanisms of upward and downward translocation were different: 3) whether the translocation pattern of infiltrated a C-sugars corresponded to that of 14 C-photosynthates. Materials and MethodsSunflower (Helianthts annuus) plants were grown at 25°for 4 to 9 weeks in a growth cabinet programmed to a 13 hr photoperiod of 30,000 lux at leaf level and an 11 hr dark period. Almost all experiments were carried out with 5-week-old plants about 20 cm tall. The first or second leaf from the base of the plant at the above-mentioned stage was mainly used as the fed leaf in all the experiments. Each experiment was done with 3 plants selected both for uniformity of height and leaf size. Every datum in the tables and figures is the average value for 3 plants.Feeding. To feed 14CO2, a leaf was enclosed in a transparent photosynthetic chamber. Seventy ,uc of 14CO.) were generated and introduced into the chamber as previously described (7). The whole planit was placed under illumination of 30,000 lux for 30 min to allowv the fed leaf to fix 14CO. and at the samiie time translocate 14C-photosynthate to parts both above and below the fed leaf. 14C-sucrose or '4C-glucose was introduced into leaves by vacuum infiltration. After infiltration for 2 min, the leaf was removed from the vessel, washed with distilled water, and kept under illumination for 30 min to translocate the infiltrated 14C-sugars.Treatmnent With A TP and DNP. The ATP solution (di-potassium salt, 2 X 10-2 M in phosphate buffer, pH 6.8, 5 X 10-2 M) or DNP solution (10-4 M in phosphate buffer, pH 6.8, 5 X 10-2 M) was introduced into the fed leaf by means of vacuum infiltration. The phosphate buffer above was infiltrated into a corresponding leaf of the control plant.