Chemosensory Responses in Tetrahymena: The Involvement of Peptides and other Signal Substances1

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Abstract
Starved Tetrahymena thermophila (or cells growing in Holz's defined medium) are attracted by a chemosensory response to complex peptide mixtures as proteose peptone, yeast extract, and extracts of blood platelets containing platelet‐derived growth factor. Starved cells are also significantly attracted by mixtures of amino acids and of nucleosides of Holz's defined medium; however, no individual amino acid or nucleoside could be identified as the major chemo‐attractant.The positive chemosensory response can be abolished by cycloheximide (CHX) but is insensitive to actinomycin D and puromycin, possibly indicating that de novo RNA and protein synthesis are not necessary for a change in chemosensory behavior. Three mutants resistant to CHX show normal response in the presence of the drug.The possible role of peptides as naturally occurring food signals of Tetrahymena is discussed.