Carbon monoxide promotes flowering in Lemna gibba via a nitric oxide-dependent oxidative stress pathway.

Main conclusion: Carbon monoxide promotes flowering in Lemna gibba via a nitric oxide-dependent oxidative stress pathway involving a CO → NO → ROS signaling cascade. This novel redox-regulated mechanism offers new insights into floral transition, which is distinct from conventional photoperiod-dependent pathways. Carbon monoxide is increasingly recognized as a signaling molecule in plant systems; however, its role in reproductive development remains poorly understood. This study showed that carbon monoxide promotes flowering in Lemna gibba through a novel pathway involving nitric oxide and reactive oxygen species. Flowering occurred exclusively under long-day conditions, indicating dependency on photoperiodic cues. Inhibition of nitric oxide production suppressed the flowering response induced by carbon monoxide, and microscopic analysis confirmed elevated nitric oxide levels in treated plants. Carbon monoxide also alters cellular redox balance by reducing the activity of key antioxidant enzymes and increasing oxidative stress markers. Notably, the use of reactive oxygen species scavengers blocked the flowering response, confirming the necessity of oxidative signaling. These findings identified a unique carbon monoxide-nitric oxide-reactive oxygen species pathway that regulates flowering independently of the known photoperiodic mechanisms. This study highlights the role of redox signaling in the control of reproductive timing in aquatic plants.