Mechanism Of Anthocyanin Alleviates Cd Oxidative Damage Of Rice Leaves And Inhibits Cd Accumulation In Rice Grains

Cadmium(Cd)pollution of soil is the most common and toxic heavy metal pollutionproblem in farmland soil at present.Rice(Oryza sativa L.)has a strong ability to absorb and accumulate Cd.Cd ions not only causes toxicity to rice,but also stimulates the Cd tolerance mechanism of rice itself.Excessive Cd content of rice grains will affect the safety of crop production and human health.In recent years,foliar barrier technology has been widely used to reduce heavy metal pollution in agricultural products.As a kind of natural water-soluble flavonoids,anthocyanins have strong antioxidant ability and are the main pigment substances for reducing heavy metal toxicity.At present,there have been no reports on alleviating Cd toxicity in rice and reducing Cd accumulation in rice grains by foliar spraying of anthocyanin.The effects of surface spraying of blueberry anthocyanin on rice growth,pigment content,antioxidant system,non-protein thiol(NPT),phytochelatins(PCs)and Cd content in different tissues and subcellular structure of rice leaves were investigated by blueberry anthocyanin in vitro antioxidant experiment,rice seedling stage and the whole growth period pot experiments and field validation experiment.This study showed that the correlation among anthocyanins in rice leaves and Cd content in different tissues and rice yield under Cd stress,and indicated surface spraying of blueberry anthocyanin technology can be used in low-Cd contaminated paddy field to achieve the purpose of reducing Cd content of rice grains and safe production.The main research contents and results are as follows:(1)Unpolluted soil from agricultural park of Anhui Agricultural University and Cd-polluted paddy soil from a lead-zinc mine in Fanchang County of Wuhu City of Anhui Province were selected as the test soil.The effects of Cd stress on the rice growth,pigment content and Cd absorption and transport of five rice varieties have shown that the contents of total chlorophyll,carotenoid and anthocyanin in the leaves of colored rice(CY30,JGHG,ZYXN)were significantly higher than those of conventional rice(ZD18,SLY870).Compared with the treatment group without Cd contamination,the increasing range of anthocyanin content in conventional rice was significantly higher than that in colored rice under Cd stress in soils around lead-zinc mines.Under Cd stress,Cd content of conventional rice grains was higher than 0.2 mg/kg(the national standard of Cd content in rice grains of China),while the Cd content of colored rice grains belongs to the safe production range.The anthocyanin content of rice leaves was no significant correlation with Cd content of rice roots,but significant negative correlation with Cd content of stem leaves and rice grains.(2)Anthocyanin antioxidant experiment in vitro has showed that blueberry anthocyanin has certain scavenging ability on four different free radicals(DPPH,ABTS⁺,O^2-,·OH).The effects of surface spraying of blueberry anthocyanin on antioxidant system,non-protein thiol(NPT)and phytochelate(PCs)content in ZD18 and SLY870 rice seedling leaves have shown that compared with single Cd stress,surface spraying of 7.5 g/L blueberry anthocyanin significantly decreased the contents of O^2-,H₂O₂ and MDA content in rice leaves and increased the content of soluble protein,and stimulate the activities of antioxidant enzymes(SOD,POD,CAT,APX,GSH,ASA)and NPT and PCs content in rice leaves.Combined with the analysis of subcellular scanning electron microscopy,it was found that surface spraying of blueberry anthocyanin could effectively relieve Cd oxidative damage to cell membrane and organelles and promote rice growth.Under the same concentration of Cd stress,the anti-Cd oxidation ability of SLY870 was stronger than ZD18.(3)Unpolluted soil from agricultural park of Anhui Agricultural University was selected as the test soil.The chelating effects of surface spraying of blueberry anthocyanin on Cd absorption in SLY870 under 1.0 mg/kg and 10.0 mg/kg Cd stress have shown that surface spraying of 7.5 g/L blueberry anthocyanin under different concentrations of Cd stress can effectively promote rice growth,reduce the transport of Cd from stem leaves to rice grains and inhibit the accumulation of Cd in rice grain.Among them,under the stress of 1.0mg/kg Cd,the transport coefficient of Cd from root to stem leaves increased by 8.11%and the transport coefficient of Cd from stem leaves to rice grains decreased by 48.83%after surface spraying of 7.5 g/L blueberry anthocyanin.After surface spraying of 7.5,10.0 and12.5 g/L blueberry anthocyanins,the Cd content of rice grains was all lower than 0.2mg/kg,which met the national standard of Cd content in rice grains of China.The subcellular distribution of Cd in leaves of SLY870 was analyzed by fourier transform infrared spectroscopy showed that anthocyanins,polysaccharides,lignin,carboxylic acids,proteins,nucleic acids and other compounds in rice may form chelates with Cd ions to isolate and immobilize Cd in cell wall and organelles after surface spraying of blueberry anthocyanin,and effectively reduce the Cd content of rice grains.(4)JH1,ZD18 and SLY870 were selected as test rice varieties.The field validation experiment was carried out in the Cd-contaminated paddy fields around a lead-zinc mine in Fanchang County,Wuhu City,Anhui Province for two consecutive years.The results demonstrated that the application of charcoal and diammonium phosphate(DAP)enhanced the p H values in soils under conventional irrigation(W1),whole growth period flooding(W2),and wet irrigation(W3).With the rice growth,the p H value in farmland increased firstly and then decreased to neutral.The Eh values of soils showed a declining tendency with the increase of moisture.At the same water management condition,the available Cd content in soil and Cd content in root,stem leaves and grains of JH1 decreased as the application amount of charcoal and DAP increased,respectively.The application of 15.00g/m² DAP coupled with W2 water treatment could be adopted to promote rice yields,which simultaneously decreased the accumulation of Cd in rice grains.The rice yields were negatively correlated with the available Cd content in soil.Surface spraying of 7.5g/L and 10.0 g/L blueberry anthocyanin could effectively promote the growth of ZD18 and SLY870,while reducing the transport of Cd from stem leaves to rice grain,and the Cd content of rice grains were lower than 0.2 mg/kg.The Cd content in rice grain had a significant negative correlation with anthocyanin content in leaves and rice yield.The rice yield of SLY870 was significantly increased by 5.24%after surface spraying of 7.5 g/L blueberry anthocyanin.Blueberry anthocyanins could be used as a foliar resistance control agent in Cd-contaminated paddy fields in this lead-zinc mine area,and selecting SLY870as the local conventional rice could achieve safe production and high yield.