Antioxidant properties of dihydroxy B-ring flavonoids modulate circadian amplitude in Arabidopsis

Flavonoids are abundant specialized metabolites produced by plants for a range of functions, including pigmentation, hormonal signaling, UV protection, and drought tolerance. We previously showed that flavonoids also influence the circadian clock in Arabidopsis Here, we report that the antioxidant properties of dihydroxy B-ring flavonoids are responsible for influencing the amplitude of the core clock gene luciferase reporter, TOC1:LUC We found the elevated amplitude of TOC1:LUC rhythms correlates with the elevated cellular H₂O₂ content of flavonoid-deficient seedlings. Moreover, two different chemical approaches to reduce the accumulation of reactive oxygen species rescued the elevated TOC1:LUC amplitude in flavonoid-deficient seedlings, whereas chemically reducing auxin transport, a known function of flavonoids, had no impact. Interestingly, Ca²⁺ levels in the chloroplast, but not the cytosol, were also altered in flavonoid-deficient seedlings, hinting at retrograde signaling as a possible target of flavonoid action. This study advances our understanding of the relationship between flavonoids and the circadian clock, as well as the mechanisms underlying this interaction.