NEGATIVE NECROTAXIS

We studied necrotaxis in several strains of protists and compared the reaction of living cells in the vicinity of cells killed by a ruby las er. Negative necrotaxis was observed for the unicellular green alga Eu glena gracilis, whereas Chlamydomonas was shown to exhibit positive ne crotaxis. The cellular colony Pandorina morum exhibited no reaction to the killing of nearby colonies. Both the colorless cryptomonad Chilom onas paramecium and the ciliate Tetrahymena pyriformis exhibited negat ive necrotaxis following the lysis of vitally stained specimens of the ir own species. They also exhibited negative necrotaxis following the lysis of Euglena cells. It was also demonstrated that the cellular con tent of Euglena cells lysed by heat or by a mechanical procedure acts as a repellent to intact Euglena cells. These results suggest that the negative necrotaxis provoked in Euglena by the laser irradiation is p robably due to the chemotactic effect produced by the release of cell content in the extracellular medium. This cell content could, accordin g to its chemical composition, act either as a repellent, an attractan t, or be inactive. The sensitivity of cells (specific or nonspecific i on channels or chemoreceptors) are also of prime importance in the pro cess.