Foliar dewdroplet–induced redox cascades promote early flowering in <i>Brassicaceae</i> plants

Atmospheric water inputs such as dew are often overlooked in plant biology. We show that foliar dewdrops act as biochemical microreactors that trigger flowering in <i>Arabidopsis thaliana</i>, a small plant from the mustard family (<i>Brassicaceae</i>). These droplets generate reactive oxygen species that induce intracellular nitric oxide accumulation, initiating a redox cascade that suppresses the biosynthesis of abscisic acid, which contributes to the regulation of flowering time. This occurs via S-nitrosylation-mediated activation of histone deacetylase 19, which silences <i>AAO3</i> and <i>ABA2</i>. Analysis of over 12 million field records across the <i>Brassicaceae</i> family reveals a global correlation between dew point temperature and flowering time. These findings identify dewdrop chemistry as an unrecognized environmental cue that regulates developmental timing in plants.