ELECTRON MICROSCOPIC OBSERVATIONS ON TUBULAR STRUCTURES INVOLVED IN CRYSTAL FORMATION IN THE RED ALGA PLEONOSPORIUM SQUARRULOSUM (HARV.) ABBOTT1

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Abstract
Hexagonal or angular crystalline inclusions in Pleonosporium (Naeg.) Hauck vegetative cells were examined using electron microscopy. Ultrastructural analysis reveals that the inclusions initially contain tubular elements resembling microtubules but, with continued differentiation, are transformed into rod containing crystals. The tubular structures initially measure 25 nm in diameter. Scattered tubules become arranged in a parallel and alternate pattern and undergo subsequent enlargement to approximately 29 nm. Following enlargement, each tubule apparently disaggregates into rods that form a crystal having hexagonally arranged rod‐like subunits. It is suggested that these tubules may represent microtubules and the resultant crystals are composed of tubulin.