Heme Oxygenase-1Cooperates With Hydrogen Peroxide To Regulate The Programmed Cell Death Of Rice Aleurone Layers Under Drought Stress

Seed germination is a initial stage of plant growth and development. After sowing, whether or not seeds germinaties normally and rapidly, so as to achieve the early formation of seedling, full seedling and healthy seedling, this relates to the high yield in agriculture. Cereal seeds germination is accompanied by the programmed cell death of aleurone layer, and it is a critical event in germinating seeds, which determines whether or not the seeds germinate normally.As a stress factor, drought can limit seeds germination by restricting its imbibition, inducing the accumulation of reactive oxygen species, thereby causing harm to the seeds. Heme oxygenase-1(HO-1) is a rate-limiting enzyme of CO synthesis in plant, which regulates seeds germination, plant growth and development. Hydrogen peroxide (H2O2) is a kind of reactive oxygen molecules, which can cause metabolic disorders by damaging the macromolecular substances in cells, while it can be used as a signaling molecule involved in some physiological activities in cells.In the study, rice (Oryza sativa L.) variety,’You Ⅱ128’seeds were treated with different treatments to explore the HO-1and H2O2regulated programmed cell death mechanism of aleurone layer in germinating rice seeds under drought stress by means of pharmacology, biochemistry, molecular biology and microscope technology. The results indicated that PEG and exogenous H2O2alone could significantly inhibit HO-1gene expression, HO-1activity, and amylase activity, also increase the content of H2O2and accelerate the programmed cell death in rice aleurone layers. However, exogenous H2O2combined with PEG treatment effectively alleviated the effects of drought stress on the HO-1gene expression level and activity of HO-1, and the amylase activity in the aleurone layer of rice seeds, while reducing the content of H2O2and properly delaying the programmed cell death of aleurone layer in rice seeds under drought stress. HO inducer, hematin, enhanced HO-1gene expression level, HO-1activity and amylase activity, but reduced the content of H2O2in the aleurone layers of rice seeds under drought stress.The inhibitor of HO-1, ZnPPIX, reversed the above effects of HO-1. The HO-1inducer hematin, NO donor sodium nitroprusside (SNP) and cGMP analogues8-Br-cGMP effectivelly delayed the programmed cell death of aleurone layer in rice seeds under drought stress. Furthermore, the effect of HO-1on the programmed cell death of rice aleurone layers could be reversed by its own inhibitor and NO scavenger. Although the effect of NO on the programmed cell death of rice aleurone layer could be reversed by its own scavenger, it could not be reversed by the HO-1inhibitor. The effect of NO on the programmed cell death of rice aleurone layers was also inhibited by cGMP scavenger, but the effect of cGMP on the programmed cell death of rice aleurone layers could not be prevented by NO scavenger. The effect of exogenous H2O2on the programmed cell death of rice aleurone layers could be reversed by its own synthetase inhibitor and cGMP scavenger. However, H2O2synthetase inhibitor could not stop the effect of cGMP on the programmed cell death of rice aleurone layers.Overall, the above results suggested that H2O2might be an upstream signaling molecules of HO-1in regulating the aleurone layers PCD of rice seeds induced by drought stress, and HO-1regulated the programmed cell death of aleurone layer through NO、cGMP and amylase.