Organisms use circadian clocks to synchronize physiological processes to anticipate the Earth's day-night cycles and regulate responses to environmental stresses to gain competitive advantage 1 . While divergent genetic clocks have been studied extensively in bacteria, fungi, plants, and animals, a conserved circadian redox rhythm has only recently been reported and hypothesized to be a more ancient clock 2, 3 . However, it is controversial whether the redox rhythm serves as an independent clock and controls specific biological processes 4 . Here, we uncovered the coexistence of redox and genetic rhythms with distinct period lengths and transcriptional targets through concurrent metabolic and transcriptional time-course measurements in an Arabidopsis long-period clock mutant 5 . Analysis of the target genes indicated regulation of the immune-induced programmed cell death (PCD) by the redox rhythm. Moreover, this time-of-day-sensitive PCD was eliminated by redox perturbation and by blocking the signalling pathway of the plant defence hormones jasmonic acid/ethylene, while remaining intact in a genetic-clock-impaired line. We demonstrate that compared to robust genetic clocks, the more sensitive circadian redox rhythm serves as a signalling hub in regulating incidental energy-intensive processes, such as immune-induced PCD 6 , to provide organisms a flexible strategy to prevent metabolic overload caused by stress, a unique role for the redox oscillator.