Hydrogen peroxide (H₂O₂) is a reactive oxygen species (ROS) that plays a dual role in plant cells. Here, we discovered that drought (20% polyethylene glycol-6000, PEG)-triggered decreases of HO-1 transcript expression and HO activity. However, exogenous H₂O₂ contributed toward the increase in HO-1 gene expression and activity of the enzyme under drought stress. Meanwhile, the HO-1 inducer hematin could mimic the effects of the H₂O₂ scavengers ascorbic acid (AsA) and dimethylthiourea (DMTU) and the H₂O₂ synthesis inhibitor diphenyleneiodonium (DPI) for scavenging or diminishing drought-induced endogenous H₂O₂. Conversely, the zinc protoporphyrin IX (ZnPPIX), an HO-1-specific inhibitor, reversed the effects of hematin. We further analyzed the endogenous H₂O₂ levels and HO-1 transcript expression levels of aleurone layers treated with AsA, DMTU, and DPI in the presence of exogenous H₂O₂ under drought stress, respectively. The results showed that in aleurone layers subjected to drought stress, when the endogenous H₂O₂ level was inhibited, the effect of exogenous H₂O₂ on the induction of HO-1 was enhanced. Furthermore, exogenous H₂O₂-activated HO-1 effectively enhanced amylase activity. Application of 8-bromoguanosine 3',5'-cyclic guanosine monophosphate (8-Br-cGMP) (the membrane permeable cGMP analog) promoted the effect of exogenous H₂O₂-delayed PCD of aleurone layers in response to drought stress. More importantly, HO-1 delayed the programmed cell death (PCD) of aleurone layers by cooperating with nitric oxide (NO), and the delayed effect of NO on PCD was achieved via mediation by cGMP under drought stress. In short, in rice aleurone layers, exogenous H₂O₂ (as a signaling molecule) triggered HO-1 and delayed PCD via cGMP which possibly induced amylase activity under drought stress. In contrast, as a toxic by-product of cellular metabolism, the drought-generated H₂O₂ promoted cell death.

#	Concept	H-Index	Publications	Citations
1	Medicine	1	1	12
2	Natural Sciences	1	1	12
3	Biology	1	1	12
4	Developmental Biology	1	1	12
5	Genetics	1	1	12

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