Nitric Oxide and Cyanide Enhance Flowering in Lemna gibba Through a Stress-Mediated Pathway Under Inductive Conditions

Nitric oxide serves as a pivotal signaling molecule that governs diverse physiological processes in plants, including the regulation of flowering. This study elucidates the interplay between nitric oxide and cyanide signaling in modulating floral induction in Lemna gibba, a model long-day plant, under photoperiodic inductive conditions. Through a systematic investigation of three distinct nitric oxide donors, sodium nitroprusside, S-nitroso-N-acetyl-DL-penicillamine, and 3-morpholinosydnonimine, we demonstrated concentration-dependent flowering promotion, with maximal responses observed at donor-specific optimal concentrations. The complete reversal of this stimulation by the nitric oxide scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide established nitric oxide as the central mediator. Notably, cyanide-induced flowering exhibited identical dependence on nitric oxide signaling, as evidenced by both chemical inhibition and direct measurement of elevated endogenous nitric oxide levels. Physio-biochemical investigations revealed that nitric oxide donors activate endogenous synthesis pathways, as flowering is suppressed by inhibitors of both nitrate reductase and nitric oxide synthase. The involvement of oxidative stress signaling was confirmed through multiple lines of evidence: flowering induction correlated with increased lipid peroxidation, alterations in antioxidant enzyme activities, and partial suppression by reactive oxygen species scavengers. Our findings establish a novel stress-mediated flowering pathway, wherein nitric oxide and cyanide converge through shared oxidative signaling mechanisms. These results provide fundamental insights into plant reproductive control and open new avenues for manipulating flowering timing in agronomically important species through targeted modulation of nitric oxide signaling networks.