The coupling effects of some thiol and other sulfur-containing compounds on the circadian rhythm of cell division in photosynthetic mutants of Euglena

Previous work has demonstrated a persisting, free-running, circadian rhythm of cell division in the P₄ZUL photosynthetic mutant of the alga Euglena gracilis Klebs (Strain Z) Pringsheim grown organotrophically in continuous light or darkness at 19° C following prior synchronization by a repetitive LD: 10,14 light cycle. A similar circadian rhythmicity has been recently discovered in the W₆ZHL heat-bleached and the Y₉ZNalL naladixic acid-induced mutants of Euglena grown under comparable conditions. Over extended timespans, however, these mutants appear to gradually lose first their ability to display persisting overt rhythms, and then even their capability of being entrained by imposed LD cycles. These properties can be restored by the addition of certain sulfur-containing compounds to the medium including cysteine, methionine, dithiothreital, sodium monosulfide, sodium sulfite, and sodium thiosulfate, as well as thioglycolic [mercaptoacetic] acid. The implications of these findings toward biological clock mechanisms are discussed: It appears that some sort of coupling process is operating as opposed to the initiation of an underlying oscillation.Non-Standard Abbreviations LL continuous illumination - DD continuous darkness - LD repetitive light-dark cycle - SS stepsize - period of biological rhythmSupported by research grants (GB-36287, GB-43543) from the National Science Foundation.Reports on portions of this work were presented at the 19th Annual Meeting of the Biophysical Society, Philadelphia, Pennsylvania, February 19–21, 1975; at the XII International Botanical Congress, Leningrad, U.S.S.R., July 3–10, 1975; and at the XII International Conference of the International Society for Chronobiology, Washington, D.C., August 10–13, 1975.