Chemical defense by means of pigmented extrusomes in the ciliate Blepharisma japonicum

The defensive function of pigment granules in Blephdrisma japonicum against the predatory ciliate Dileptus margaritifer was further investigated by 1) observing the discharge of pigment granules of Blepharisma as a response to the attack by the predator and 2) measuring the toxicity of purified blepharismin, the red pigment localized in pigment granules. When a Blepharisma was attacked by the toxi-cysts-bearing proboscis of a Dileptus, the Blepharisma instantly released a mass of reddish material at the attacked site. The Dileptus retreated and the Blepharisma swam away. The observation suggested that the Blepharisma discharged pigment granules as a response to the attack. This assumption was confirmed by scanning-electronmicroscopic observations; many pigment granules near the attacked site were discharged at the moment of the attack. Purified blepharismin was highly toxic to Dileptus and several other ciliates, but was not toxic to Blepharisma. We also showed that blepharismin is toxic in the dark. These results strongly support the previously presented hypothesis that the defensive function of pigment granules in B. japonicum against D. margaritifer is based on the discharge of blepharismin as a response to the attack by the predator. We conclude that pigment granules of B. japonicum are extrusomes (extrusive organelles in protists) for chemical defense.