[(14)C-Microautoradiography of water-soluble substances in the phloem]

A method for the preparation of microautoradiographs for plant tissues is described. The procedure is as follows: the frozen tissue is lyophilized, dissected into small pieces, fixed with paraformaldehyde vapor, infiltrated in vacuo with xylene, impregnated with silicon oil in xylene, and transferred step by step into embedding resin (Durcupan ACM, Fluka). The trimmed blocks are sectioned with glass knives on an ultramicrotome into 1 μm thin sections, which are transferred to microscope slides, stretched, stained with gentiana violet, coated with stripping-film (Kodak AR 10), exposed at 4° C, and processed as usual.The treatment with paraformadehhyde fixes the cytoplasmatic structures and keeps amino acids in position; the siliconization prevents the leakage of sugars out of the floating sections. Thus, probably all water-soluble assimilates occurring in sieve elements can be kept in their original position.Examples of microautoradiographs are depicted. They show homogeneously labeled sieve elements and no accumulations of tracers near the sieve plates. The companion cells are partly labeled, partly unlabeled; they certainly are not concerned with long distance translocation.This method makes possible the examination of serial sections. The percentage of successful preparations is very high, nearly 100%.