Vinblastine-induced precipitation of phloem proteinsin vitro

Summary Purified proteins from sieve tubes ofCucurbita maxima were precipitated with vinblastine and the precipitates were analyzed with the electron microscope. Filaments (35–40 Å in diameter) and tubular structures (160 Å in width) were observed in negatively stained preparations. The predominant structures of the negatively stained and of the thin sectioned material, however, were membrane-like sheets (100–120 Å in width) which showed the typical unit membrane aspect.Dedicated to Professor Dr. W.Schumacher on his 70th birthday.The investigations were supported by the Deutsche Forschungsgemeinschaft.