Effects Of Hydrogen Peroxide On The Regulation Of Iron Plaque Formation Induced By Phosphorus Deficiency In Rice

Phosphorus is a large amount of nutrients necessary for the growth of crops,and phosphorus deficiency restrict the high yield and quality of crops.Low phosphorus or phosphorus deficiency induce the formation of iron plaque on the root surface of rice.Among various reactive oxygen species,the production and physiological functions of H₂O₂ under stress in plants have attracted people’s attention in recent years.H₂O₂has always been regarded as a toxic by-product of aerobic metabolism in plants,which cause oxidative damage to macromolecules such as proteins,lipids and DNA in plants.However,recent researches show that H₂O₂ maybe has a dual role.When the content of H₂O₂ continuously produced by peroxidation is high,it is a cytotoxic molecule.When the content of H₂O₂ is low,it is involved in signal transduction pathway leading to plant defense against stress response,aging,programmed cell death,and plants signal molecules for growth and development expression.However,the associations of phosphorus starvation with H₂O₂ generation,iron plaque formation and the H₂O₂origin are still unclear.The present study investigated the effects of phosphorus deficiency on iron plaque formation,H₂O₂ production and antioxidant defense systems,the effect of H₂O₂ pretreatment on phosphorus-deficiency induced iron plaque formation.The potential souce of H₂O₂ and its effect on iron and phosphorus uptake,transduction and accumulation in japonica rice Nipponbare and indica rice Zhefu 802.The aim of this research is to clarify the role of H₂O₂ signaling in regulating phosphorus deficiency-induced iron plaque formation,and screen out H₂O₂concentration that can promote iron plaque formation and enhance rice’s own protection mechanism,providing new ideas for improving rice resistance.The main research results obtained are as follows:（1）Hydroponic method was used to induce the formation of iron plaque in rice root by different time（0,4,8,12,24 h）phosphorus deficiency and different concentration of exogenous H₂O₂（0,20,40,60,80,100μmol/L）,so as to clarify the relationship between root H₂O₂ production and iron plaque formation,and to screen out the optimal H₂O₂ concentration to induce iron plaque formation.The results showed that after treatment with phosphorus deficiency for 48 h,the total root length of Nipponbare and Zhefu802 increased by 199.59%and 24.42%,the total root surface area increased by 256.14%and 25.13%,the dry weight of shoot decreased by 10.63%and 19.51%,and the dry weight of roots decreased by 28.2%and 6.56%,respectively.It showed that a longer time（48 h）of phosphorus-deficient culture increased the total root length and root surface area,but decreased the plant dry weight.With the increase of phosphorus deficiency time,the formation of iron plaque on the root surface increased rapidly.The root peroxidase（POD）activity and H₂O₂ content increased within 0-4 h of phosphorus deficiency and then decreased,and returned to a stable state at 24 h,indicating that changes in root H₂O₂ content were related to changes in root POD activity.Compared with the control,the relative elongation of Nipponbare and Zhefu802 roots pretreated with 20μmol/LH₂O₂ were 120.00%and 107.14%,respectively,and the increase in root surface iron plauqe content was 36.93%and143.41%,both reached the maximum.Therefore,20μmol/LH₂O₂ was used as the concentration for subsequent experiments.（2）Investigate the effect of H₂O₂ on phosphorus deficiency-induced iron plaque formation on rice root surface and the absorption of Fe and P by adding H₂O₂scavengers（CAT and DMTU）.The results showed that the H₂O₂ scavenger treatment reduced the endogenous H₂O₂ content and iron plaque thickness of the roots of Nipponbare and Zhefu802.The root H₂O₂ content decreased by 26.90%and 32.66%under-P+CAT+DMTU treatment compared with-P+H₂O₂ treatment.The distribution of Fe in the two rice root showed a downward trend after phosphorus-deficient culture,and decreased to the minimum after-P+H₂O₂ treatment.Scavenger treatment alleviated the decline in Fe distribution in the root system.In addition,the-P+H₂O₂ treatment had a higher DCB-P and shoot P distribution and a lower root P distribution than all the phosphorus deficient treatment groups.It shows that the exogenous application of H₂O₂is beneficial to the formation of iron plaque on the surface of rice roots.Thicker iron plaque may inhibit the absorption of Fe by the root and reduce the accumulation of Fe in the root and aboveground.At the same time,the increase of iron plaque formation promotes the accumulation of P on the iron plaque and the transfer from the root surface and root of rice to the shoot.（3）Investigate the relationship between the POD activity of two rice genotype roots and the production of H₂O₂ and the effect on Fe and P absorption under phosphorus deficiency by adding an H₂O₂ endogenous inhibitor.The results showed that typeⅢPOD inhibitors（SHAM）significantly reduced POD activity,endogenous H₂O₂ content and iron plaque content,aggravated the inhibition of shoot and root growth under phosphorus deficiency,reduced the absorption of Fe by rice and reduced the use of own P.It shows that typeⅢPOD is the main source of H₂O₂ produced by rice roots under phosphorus deficiency.In summary,in the early stage of phosphorus deficiency,rice increased the content of POD and decreased the content of CAT to promote the massive production of H₂O₂ to initiate the formation of iron plaque on the root surface.Pretreatment with 20μmol/L exogenous H₂O₂ significantly increased the formation of iron plaque on the root surface and the distribution of P in the iron plaque.A thicker iron plaque may inhibit the absorption of Fe by the root system and reduce the accumulation of Fe in the root and shoot.At the same time,the increase of iron plaque formation promoted the accumulation of P on the root surface iron plaque and the transfer from the root surface and root system of rice to the shoot.It is preliminarily judged that most of the H₂O₂involved in the initiation of iron plaque formation comes from the H₂O₂ produced by the consumption of O₂ by type III POD.