Potential mechanisms for the rapid post-drought reversal of ABA-induced stomatal closure by melatonin, 5-aminolevulinic acid, and brassinosteroids.

The regulation of stomatal movements is crucial for plants to optimize gas exchange and water balance. The plant hormone abscisic acid (ABA) triggers stomatal closure in response to drought, effectively minimizing water loss to prevent hydraulic failure. However, it significantly constrains photosynthesis, restricting plant growth and productivity. Therefore, rapid post-drought stomatal opening is crucial for earlier photosynthetic recovery. This review explores how phytohormones or plant growth regulators reverse ABA-induced stomatal closure. Phytomelatonin, 5-aminolevulinic acid, and brassinosteroids promote stomatal reopening by either ABA degradation or suppressing its biosynthesis through the downregulation of corresponding genes. This results in less ABA-induced H₂O₂ accumulation in guard cells, which lowers H₂O₂-triggered Ca²⁺ levels in guard cells, and promotes the opening of KAT1 (K⁺ _in channels). Insights from this review highlight the potential mechanisms of stomatal reopening for earlier post-drought gas exchange recovery, offering potential avenues to enhance plant productivity under changing environmental conditions.