An Autoradiographic Technique for Detailed Studies with Plant Tissue

Within the past few years, reports in the literature indicate the increasing use of detailed autoradiographic techniques in problems concerned with the location of areas of deposition or concentration of radioactive isotopes in animal tissue. The usefulness and value of these techniques has increased with the availability of special nuclear track emulsions and the development of suitable laboratory procedures. These autoradiographic techniques have not been fully utilized in studies of plants although Arnon et al. (1), Colwell (2), Harrison et al. (8), and Gross and Snyder (6) have used the gross or survey autoradiographic techniques. Several procedures have been used in conjunction with animal studies; and with minor modifications, these can be adapted to plant materials. A general review of these techniques as applied to animal studies has recently appeared in the literature (7). One of the techniques provides for a permanent mounting of the histological sections on the photographic emulsion throughout the exposure and processing periods, and it is this one that was used in the study. This method was first used with animal tissue by Endicott and Yagoda (4) and Evans (5). Microscopic examination with both high-dry and oil-immersion objectives is possible, and the deposited silver grains can be correlated with the tissues and cells containing the radioisotope. Sections taken from Hydrangea leaves that had been exposed to an atmosphere containing radioactive carbon dioxide (C1402) for four hours were used in this study. Details of the chamber which was used and the procedure which was followed have been previously reported (3). At the end of the period of photosynthesis, the leaves were separated from the plants and rinsed with dilute hydrochloric acid to remove adsorbed Cu02. Small strips were cut from the leaves and placed in an FAA fixing solution. The leaf tissue was then dehydrated and embedded in paraffin following usual procedures. Sections 15 microns in thickness were cut on a rotary microtome. Praffin ribbons of the desired length were expanded in warm water at 42? C. Following expansion, the ribbons were transferred to water at 18 to 20? C. The ribbons hardened at these lower temperatures and could be handled more easily during subsequent operations. In the dark room, Eastman nuclear track plates of the NTB or NTB2 type were soaked in distilled water at 20? C for five minutes. The ribbons were removed from the water with a section lifter or a small hair brush and placed on the swollen emulsion. This manipulation was conducted under a Wratten safelight, series 2. Soaking the plates prior to placing the ribbons in contact with the emulsion ensures good adhesion between sections and