An approach to the study of the physiological control of translocation in higher plants.

Tne elective or tnis -nvestiga^icn v/a^ to ?\u27-,?ai.\u27. __.e insight into wnat limits or cor.trc^ transl^catior. i:" hi /. ~ plants. ?/ Photosynthesis and trans location xv^r^ studied v..,_.\u27.-v ^""CO.-,. Over 75% of the assimilated ~ c W?s incorporated into surcro~e via aspartic acid and malic acid. About 20% cf the "^C v.vnt _..tc ethanoi-insoluble compounds. Lowering the temperature to o" \u27?? ?delayed the incorporation of the ^ ""C i^to sucrose, out hac. little effect on the rate or amount of incorporation. In young corn plants all the leaves exported C, most of which went to the roots and the growing regions of the plants. Ail the leaves imported some 14G assimilated in other leaves. The only translocated organic compound in corn was sucrose-It was translocated down the leaf blade at a velocity in excess of 150 cm hour . The transiocation profile in the leaf blade v/as logarithmic and was found to be due to a reversible accumulation of t;.e translocate in the vascular tissue. Corn leaves were used to establish a method for measuring 14 transiocation from the leaf. Measuring the amount of C remaining in the fed area of leaf at various times after feeding ""^2 provided information on 3 characteristics of translocaticn; the relative rate of transiocation from the leaf, the total percentage of the assimilated C that is translocated, and the turnover time of the transiocation pool. From these measurements the transioca- tion in corn at 2600 ft-c was calculated to be 327 ugm of sucrose -2 -i d.;. mm . The turnover time of the transiocation pool in corn v,-_s 80 minutes. This method was used to study the effect of different factors on transiocation from the leaf. A decrease in te:..oari.tu.^ decreased the rate of translocation more or less linearly from 26 to 7? The turnover time of the translocation pool and the percentage of the assimilates translocated increased with a decrease in temperature. Light had no significant effect on translocation. The rate of translocation and the percentage of the assimilates translocated changed with the age of the leaf. The method of measuring the C remaining in the fed area of leaves was used in a comparative study of translocation in a number of species. The relative rate of translocation and the percentage of the assimilates translocated varied with the species. Corn, sorghum, millet and sunflower translocated between 70 and 90% of the assimilated ^C in 24 hours, whereas the other species translocated only between 40 and 60%. The compounds in which the 14C was held back in the leaf varied with the species. The turnover time of the translocation pool divided the species into 2 groups; tomato and radish had a turnover time of 40 minutes, all the other species had a turnover time of about 80 minutes. The result of the investigations suggest that the limiting process in translocation is the transfer of the translocate from the assimilating cells to the phloem. It is speculated that the main part of the control of translocation is at the membranes of the exporting cells