| Cadmium(Cd)is a nonessential toxic heavy metal of animals and plants.It is one of the most seriously threatened farmland pollutants.Rice is one of the main grain crops in China.Most of the population in our country is fed by rice.After being polluted by Cd,it is easy to accumulate in plants and cause serious health damage to the human body.This study is divided into two parts: seedling experiment and seedling experiment.After a week of 50 mol/L Cd Cl2 pretreatment,the seedlings were treated with different combinations of magnesium,silicon,calcium and amino acid(G1-G6)for two weeks.The accumulation and transport of Cd,photosynthetic system and oxidative damage level of rice seedlings were measured,and the alleviating effects of different treatments on Cd toxicity of rice were analyzed.The treatments as follows:G1:H2O(Control group)G2:Na SA(5mmol/L)G3:Na SA(5mmol/L)+ Mg Cl2(2mmol/L)+ Glu(2mmol/L)G4:Na SA(5mmol/L)+ Na2 Si O3(2.5mmol/L)G5:Na SA(5mmol/L)+ Mg Cl2(2mmol/L)+ Glu(2mmol/L)+ Ca Cl2·2H2O(2.5mmol/L)G6:Na SA(5mmol/L)+ Mg Cl2(2mmol/L)+ Glu(2mmol/L)+ Na2 Si O3(2.5mmol/L)After 200 μmol/L Cd Cl2 pretreatment,the mature seedling experiment,the growth of rice seedlings,the accumulation and transport of Cd,the content of photosynthetic pigments and the accumulation of mineral elements were measured by different combinations of magnesium,silicon,calcium and amino acids(G1-G6)for two months.The alleviating effects of different treatments on Cd toxicity in rice were studied.The main results are as follows:(1)In the seedling experiment,G2-G6 decreased the accumulation of Cd in the shoot and root of rice seedlings under Cd stress,reduced the transport coefficient of the subsurface to the top of the ground,increased the content of photosynthetic pigments in the leaves of rice,enhanced the net photosynthetic rate and the CO2 concentration in the intercellular space,increased the stomatal conductance and transpiration rate of the leaves.The maximum photochemical efficiency and actual photochemical efficiency were improved,the nonphotochemical quenching was reduced,and the normal operation of the photosynthetic system of rice seedlings was maintained,the content of malondialdehyde in the upper and root parts of rice was reduced significantly,and the accumulation of hydrogen peroxide and superoxide anion was reduced,the combination of the treatment decreased by about 40%,which reduced the oxidative damage of rice seedlings.Among them,the reduction of Cd content in the shoot of rice seedlings was the most obvious,which was reduced by 60.22%,and the transport coefficient of the subsurface to the ground was reduced by 60.22%,and the ratio of Cd to the photograph was reduced by 43.58%.G6 increased the content of Chl a and Chl b in the leaves of rice seedlings under Cd stress,which was 88.68% and 98.91 higher than that of the control.The effects of G6 on light and gas exchange parameters and chlorophyll fluorescence parameters of young rice seedlings were significantly higher than those of control.Compared with the control,the net photosynthetic rate increased by 96.51%and the maximum photochemical efficiency increased by 82.25%.(2)In the mature seedling experiment,G2-G6 increased the biomass of rice,rice husk,leaf,stem and root of rice seedlings.The biomass of rice increased by 48.57% and the yield increased significantly under the G6 treatment.G2-G6 increased the number of panicles per spike and the number of grains per panicle.The number of spikes of G6 increased by 51.03%,and the ratio of grain number per panicle was compared.The G2-G6 decreased the accumulation of rice,rice husk,leaf,stem and root Cd under Cd stress,reduced the transport coefficient of the root to the ground and the leaf to grain.The Cd content of rice was reduced by 86.61%,and the transfer coefficient of the root to the ground was 44.72% lower than the control under the G6 treatment.The transport coefficient of grain was reduced by 75%;G2-G6 increased the content of Chl a,Chl b,Chl a+b and Car.Chl a increased by 79.8% under G6 treatment.Chl content increased by 64.91% compared with the control.The amount of Ca,Mg,Cu,Fe,Mn and Zn absorbed by rice promoted the accumulation of mineral elements in rice.Under the G6 treatment,the Cu content of rice increased by 71.7% compared with the control,while the Fe content increased by 69.53%,reaching a significant level.(3)Salicylic acid can reduce membrane lipid peroxidation and alleviate the inhibitory effect of Cd stress on plant growth.Glutamic and magnesium ions promoted the synthesis of magnesium protoporphyrin,which led to the chloroplast signal,which promoted the expression of cadmium resistant genes,especially the expression of antioxidant genes and cadmium transporters,and further improved the resistance of rice to Cd.Ca2+ can play a competitive point with free Cd2+ on the surface of biofilm,thus reducing its biological toxicity and playing a competitive protective effect,thus alleviating the biological toxicity of Cd.Silicon increased soil p H value,and the combination of silicic acid and active cadmium formed stable substances,which reduced the proportion of soil available cadmium and reduced the toxicity of Cd.On the other hand,the deposition of silicon binding proteins in the endodermis and fibrous cell regions of the roots of rice reduced the Cd transport of the apoplast.Our results confirm that the effect of metasilicate on cadmium is better than that of calcium ions at the same concentration,and the specific cytological mechanism needs further study.The combination of glutamic acid,magnesium and silicic acid in this study reduced the Cd content of rice rice with Cd content by 86.61%,and reduced the Cd content of Cd contaminated rice to less than the safety value. |
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