Polyamine regulates tolerance to water stress in leaves of white clover associated with antioxidant defense and dehydrin genes via involvement in calcium messenger system and hydrogen peroxide signaling

Endogenous polyamine (PA) may play a critical role in tolerance to water stress in plants acting as a signaling molecule activator. Water stress caused increases in endogenous PA content in leaves, including putrescine (Put), spermidine (Spd), and spermine (Spm). Exogenous application of Spd could induce the instantaneous H(2)O(2) burst and accumulation of cytosolic free Ca(2+), and activate NADPH oxidase and CDPK gene expression in cells. To a great extent, PA biosynthetic inhibitor reduced the water stress-induced H(2)O(2) accumulation, free cytosolic Ca(2+) release, antioxidant enzyme activities and genes expression leading to aggravate water stress-induced oxidative damage, while these suppressing effects were alleviated by the addition of exogenous Spd, indicating PA was involved in water stress-induced H(2)O(2) and cytosolic free Ca(2+) production as well as stress tolerance. Dehydrin genes (Y(2)SK, Y(2)K, and SK(2)) were showed to be highly responsive to exogenous Spd. PA-induced antioxidant defense and dehydrin genes expression could be blocked by the scavenger of H(2)O(2) and the inhibitors of H(2)O(2) generation or Ca(2+) channels blockers, a calmodulin antagonist, as well as the inhibitor of CDPK. These findings suggested that PA regulated tolerance to water stress in white clover associated with antioxidant defenses and dehydrins via involvement in the calcium messenger system and H(2)O(2) signaling pathways. PA-induced H(2)O(2) production required Ca(2+) release, while PA-induced Ca(2+) release was also essential for H(2)O(2) production, suggesting an interaction between PA-induced H(2)O(2) and Ca(2+) signaling.