PubMed · 10239320
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
1978-10-30. Different hours present different problems.. https://pubmed.ncbi.nlm.nih.gov/10239320/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The fungus Neurospora crassa is a model organism for investigating the biochemical mechanism of circadian (daily) rhythmicity. When a choline-requiring strain (chol-1) is depleted of choline, the period of the conidiation rhythm lengthens. We have found that the levels of sn-1,2-diacylglycerol (DAG) increase in proportion to the increase in period. Other clock mutations that change the period do not affect the levels of DAG. Membrane-permeant DAGs and inhibitors of DAG kinase were found to further lengthen the period of choline-depleted cultures. The level of DAG oscillates with a period comparable to the rhythm of conidiation in wild-type strains, choline-depleted cultures, and frq mutants, including a null frq strain. The DAG rhythm is present at the growing margin and also persists in older areas that have completed development. The phase of the DAG rhythm can be set by the light-to-dark transition, but the level of DAG is not immediately affected by light. Our results indicate that rhythms in DAG levels in Neurospora are driven by a light-sensitive circadian oscillator that does not require the frq gene product. High levels of DAG may feed back on that oscillator to lengthen its period.
We investigated whether cellular responses to various stress conditions are regulated in synchronization with the ultradian rhythm of respiratory-fermentative metabolism which is coupled to the cell cycle rhythm in continuous cultures of the yeast Saccharomyces cerevisiae. The cellular resistance to heat oscillated with a peak at the late respiro-fermentative phase, which approximately corresponds to the unbudding period of the cell cycle. Cellular resistance to H(2)O(2) and that to the superoxide-generating agent menadione oscillated in the same phase as that of heat resistance. The resistance to cadmium and that to 1-chloro-2,4-dinitrobenzene, an uncoupler of energy metabolism in mitochondria, both oscillated with a peak advanced by about 80 degrees relative to that of heat resistance, approximately covering the respiro-fermentative phase. Thus, cellular resistance to various stresses in S. cerevisiae oscillated in synchronization with the metabolic oscillation in the continuous culture.
In a recent experimental study, Ouyang et al. (1998, Proc. Natl. Acad. Sci. U.S.A.95, 8660-8664) have shown that, in direct competition, cyanobacterial strains whose circadian clocks have free-running periods (FRPs) which match the period of an imposed light/dark (LD) cycle exclude strains whose FRPs are out of resonance with the LD cycle. These differences in competitive fitness are observed despite the lack of measurable differences in monoculture growth rates between the strains. Here we show that the experimental results are consistent with a mathematical model in which cells rhythmically produce a metabolic inhibitor to which they display a sensitivity modulated by their circadian rhythm. We argue that models in which there is a circadian modulation of nutrient uptake kinetics cannot account for the results of these experiments. We discuss possible experiments to further characterize this phenomenon. The experimental protocol we propose can be used to distinguish between mutual inhibition and substrate depletion as underlying causes of the competitive advantage of circadian resonance.