The Ultra-Structure of Sieve Plates of Macrocystis pyrifera

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Abstract
Light microscope studies of fresh and preserved material of Macrocystis pyrifera showed that strands of cytoplasm or of cytoplasm-like material could be seen approaching, but not penetrating the sieve plates of the sieve tubes, especially when such cells were stained with certain compounds like magdala red and alizarin red. Occasionally bodies resembling chromoplasts were found in the cytoplasm of sieve tubes and accumulated formazan, the reduced form of tetra-zolium chloride. Aniline blue or mercuric bromphenol blue stained the callose but did not reveal strands penetrating the pores of the sieve plates. Electron microscope studies of the sieve tubes revealed that plates were penetrated with strands of an electron dense material and that the pores of the plates are not unobstructed. Whether the sieve plate was layered with callose or not, the penetrations of the pores appeared to be a continuous extension or web of material resembling the endoplasmic reticulum.