From a Single Leaf of Sunflower

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) on translocation of 14C-photosynthate from single leaves of tobacco plants, it was found that the stage of development of both the fed leaves and the seedlings affected the pattern of translocation. It was also found that a larger amount of 14C was translocated from fed leaves with higher contents of sugar phosphates, suggesting that the level of phosphorylation in a leaf could be one of the important factors that affect the rate of translocatioin of photosynthate from a fed leaf. In every tobacco plant in our previous experiments, ' 4C-photosynthate was translocated from the fed leaf both upward and downward. Studies of translocationi up to the p)resent time, have been focused mainly on downwarcd tranislocationi (1, 2, 3, 4, 5). Verv little work has been done on upward traluslocationi in comparison witlh downward trainslocation. \Vehb anid Gorlham (11) (leternihine(l the Iistribution of labeled mletabolites after the primary leaf of a squash plant had been fed with 1'4C0... Radioactivity was found in both tihe upper ancd lower sectionis of the plant. Hartt and Kortschak (4), working on upward and downward translocatioll in (letaclhed sugarcan,e blades, found that downwar(d tranislocation depended 11po11 basipetal polarity. Shiroya ct al. (8) found with white pine seedlings that a considerabhle amotunt of photosynthate was translocated upwards during the growtlh of the shoot, when downward translocation was at the lowest value of the year. The present work on sunflower plants was carried out to find: 1) what specific factors affect the rate of translocation from a fed leaf: 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 14C-photosynthates. Materials and Methods Sunflower (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 ATP 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. Extraction, Separation and Measu? enment of 14C-Compounds. After a 30-min period of photosynthesis and translocation, stems above and below 1605 www.plantphysiol.org on October 15, 2017 Published by Downloaded from Copyright © 1968 American Society of Plant Biologists. All rights reserved.