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ELECTRON MICROSCOPIC LOCALIZATION OF PHYTOCHROME IN PLANTS USING AN INDIRECT ANTIBODY-LABELING METHOD

The use of polyethylene glycol as a preembedding medium for immunocytochemistry at the electron microscope level has been adapted to the localization of phytochrome in etiolated oat (Avena sativa L., cv. Garry) seedlings. Phytochrome was indirectly labeled in 3-µm sections with rabbit antiperoxidase-peroxidase complex using sheep antirabbit serum and a specific rabbit antiphytochrome serum. Following localization the 3-µm sections were reembedded for ultrathin sectioning. In the absence of information regarding the subcellular distribution of phytochrome, it was necessary to develop a control which would demonstrate that all organelles and areas of the tissue being localized were penetrated by all reagents. Such a control is described. In those cells which contained phytochrome it was found to be generally distributed throughout the cytoplasm and to be associated with both amyloplasts and mitochondria. No activity was observed in nuclei.