Javier Pichaco, Celia M Rodriguez-Dominguez, Antonio Diaz-Espejo
Angiosperms rose to ecological dominance through innovations that enhanced photosynthetic capacity and water-use efficiency. We propose that a pivotal, yet underappreciated, contributor was the hydroactive stomatal mechanism, an abscisic acid-mediated, metabolically driven control of guard-cell turgor. Unlike passive hydraulic responses to changes in water status, hydroactive regulation enables rapid, multisignal integration and minute-scale adjustment of stomatal aperture, synchronising carbon gain with hydraulic safety under fluctuating light, CO2, and evaporative demand. We argue that this water-status control module complemented other stomatal signalling pathways responsive to light, CO2, and metabolism, improving physiological coordination in dynamic environments. This perspective reframes stomata as decision-making nodes linking leaf anatomical evolution, physiological plasticity, and angiosperm diversification and offers a foundation for engineering climate-resilient crops under climate change.