The Mechanisms Of Foliar Feeding Of Melatonin On Cadmium Tolerance Of Chinese Cabbage

In recent years,with the development of mineral resources and the emission of’three wastes’,the soil heavy metal pollution in the surrounding farmland of city is serious.Chinese cabbage(Brassica campestris L.ssp.chinensis Makino)is one of the subspecies of brassica,which is widely cultivated in China,especially in the suburbs,so it is more susceptible to heavy metal pollution.The study found that the content of Cd2+in cabbages was 0.73-2.96 mg·kg-1 in polluted regions,which was far beyond the safety standard of vegetable consumption in China,so it posed a great threat to the health of the people.Therefore,this study investigated whether foliar feeding of melatonin could relieve the Cd stress of cabbages by using Chinese cabbage as the test material,and preliminarily explored its mechanism.The main results were as follows:1.By soil culture experiment found that spraying on the leaf of different concentration of melatonin does not affect the normal growth of Chinese cabbage,but can significantly reduce the pakchoi edible part of the content of Cd2+and Pb2+,and the effect is best when it concentrations was 500 mol·L-1.By different time intervals and illumination conditions experiment found that the best effect was to spray 500 mol·L-1 melatonin per 2 d in the dark conditions.2.Cadmium stress causes the leaves to lose green and the photosynthesis is inhibited,which leads to the inhibition of the growth of Chinese cabbage seedlings.In addition,the seedling of Chinese cabbage under the stress of Cd was increased with the content of reactive oxygen(O2·-,H2O2)and malondialdehyde(MDA).And after spraying on the leaf of melatonin,compared with the single Cd treatment,Chinese cabbage seedling growth and photosynthesis related indicators are significantly increased,and associated with antioxidant enzymes(SOD,POD,APX and CAT)activity to futher improve,antioxidants(AsA and GSH)content increased,significantly reduced in the aerial parts of Chinese cabbage seedling and root of Cd2+content.By analyzing the expression of Cd2+uptake and transport-related genes(IRT1,IRT2,Nrampl,Nramp3,HMA2 and HMA4),the transcription of the above genes can be significantly down-regulated by melatonin.Synthesize the above results,the application of melatonin can improve the antioxidant activity and increase the antioxidant content to alleviate the oxidative damage of Chinese cabbage seedlings caused by Cd stress.In addition,spraying on the leaf of melatonin can down-regulate IRT1,IRT2,Nrampl,Nramp3,HMA2 and HMA4 transcription to reduce the absorption and transport to the ground of Cd2+of Chinese cabbage seedling to reduce the content of Cd2+,Cd tolerance can be improved.3.Tthe experimental results show that the content of NO was significantly increased in the seedlings of young cabbage under cadmium stress,and the content of NO was significantly reduced after spraying melatonin.Based on the NO key enzymes(NR and NOS)activity and key enzyme genes encoding(NR and NOA1)express determination found that spraying on the leaf of melatonin also restrain the activity of enzymes and reduce the gene expression level.Therefore,leaf spraying melatonin can reduce the content of NO in Chinese cabbage seedlings under Cd stress by inhibiting the biosynthesis of NO.By adding the NO donor SNP and NO scavenger PTIO,L-NMMA,Tungstate found that NO will promote Chinese cabbage by.up-regulating IRT1,IRT2 expression for the absorption of Cd2+and Fe2+ under cadmium stress condition,on the contrary,spraying on the leaf of melatonin and the PTIO,L-NMMA,Tungstate will down-regulate IRT1,IRT2 expression to reduce the absorption of Cd2+and Fe2+of Chinese cabbage seedlings.Integrate the above results,spraying on the leaf of melatonin helps relieve the stress of Cd with NO relative,NO as melatonin downstream signaling molecules involved in regulate the expression of IRT1,IRT2 to reduce the absorption of Cd2+of Chinese cabbage seedling,and reduce the accumulation of Cd2+,Cd tolerance can be improved.