THE EFFECT OF NUTRITIONAL STATE ON PHOTOREVERSAL OF ULTRAVIOLET INJURIES IN DIDINIUM NASUTUM

Abstract

Ultraviolet (UV) injury and its photoreversal were studied in the carnivorous ciliate Didinium nasutum. which feeds upon Paramecium. Didinium division is mucl more resistant to UV than that of Colpidium, being ap-preciablv retarded only after dosages of UV (2654A) of about 3000 ergs/mm2. Maximal photoreversal of such UV injury requires delivery of about 100 quanta of blue (4350A) per quantum of UV. Immediately after ingestion of a Paramecium by a Didinium its resistance to UV decreases, but within 15-60 minutes thereafter it increases. Presumably during this time protective materials are liberated from the Paramecium. Photoreversal of UV injuries to didinia is only slightly increased by feeding before exposure to visible light. Paramecia irradiated with UV until injured but not yet cytolyzing, serve as adequate food for didinia which divide at a rate comparable to controls. The bearing of the data on theories of radiation action is considered.