Preparing Whole-Leaf Radioautographs for Studying Translocation 1,2

The development of isotopic and radioautographic techniques during the past decade has provided a strong impetus for studies in many fields of plant physiology. The technique of radioautography of dried whole plants or parts of plants has been par-ticularly useful in studying translocation of organic solutes (1, 6); uptake and distributions of mineral elements (7); screening methods to establish the ef-fectiveness of herbicides (3), and host-parasite rela-tionships (8). Since the method has been so widely used it is important to examine the method critically in order to properly interpret results. In 1957 Pallas and Crafts (6) pointed out the difficulties that could be encountered when studying distribution of carboxyl-labelled 2,4-D in plant tissues. They applied a small drop of the herbicide for 1 minute to the mid vein of one primary leaf of two bean plants. Then one plant was freeze-dried and the second was pressed between blotters and air dried. Subsequent exposure to X-ray film revealed that in the air dried plant there was, during its drying, movement of label throughout the plant, while in the freeze-dried plant there was no such movement even within the leaf blade. Our paper compares radioautographs of leaves containing both C14 and p32. Such a comparison serves as a basis for choos-ing methods that do not give rise to artifacts. Materials & Methods Soybean (Glycine max) was grown in vermiculite in pots in the greenhouse. Plants with fully devel-oped primary leaves and one fully expanded trifoliate leaf (14-20 days old) were used in experiments. C1402 was administered to a restricted area on the upper surface of one primary leaf as follows. A cylindrical glass chamber was constructed, 3 cm2 in cross section and 5 cm in length with a 0.5 X 2 cm sidearm protruding half way along its length. One end of the cylinder was open and the other end closed. The chamber was of such a design that labelled-carbonate solution could be placed in the sidearm and 50 % sulfuric acid in the closed end without mixin