The Cadmium Tolerance Mechanism And Alleviation Mechanism Of Hemin In Brassica Oleracea L.

In recent years,the problem of heavy metal cadmium pollution in soils has been caused by industrial and mining industries in China,it has become increasingly serious.Cabbage is one of the most important vegetables in China.Therefore,its growth,development and quality have attracted much attention.A hydroponic experiment was carried out to study the growth,the absorption and accumulation of Cd,tolerance to Cd and genotype differences of two cabbage(Brassica oleracea L.)cultivars with different Cd-tolerance(Lufeng-Cd-sensitive and Niuxin-Cd-tolerant)under different Cd concentrations(0,10,50,100 ?moL-L"1)treatment.And the alleviation mechanism of 50?moL·L-1 hemin in cabbages under Cd Stress was also been explored.The following are the main research results:Under Cd stress,the growth of cabbages was significantly inhibited.Especially,the suppression degree of Lufeng was significantly higher than that of Niuxin.Cd was mainly distributed in the roots of cabbages,and the content of Cd in shoots of Lufeng was significantly higher than that of Niuxin.The structure of cabbage root cells was obviously deformed,the cell membrane was obviously damaged,the cytoplasm was sparse,and the vacuole increased.As the concentration of Cd increased,the degree of damage continued to increase until it was almost completely damaged.Under Cd stress,the contents of pectin,hemicellulose ?,and hemicellulose ? in the cell wall of cabbage roots were significantly increased,and the increase of Lueng was greater than that of Niuxin;the uronic acid content of each component also increased.Especially,pectin and hemicellulose ? reached significant levels,and the uronic acid content in Niuxin is higher than that in Lufeng.Cd is mainly bound to hemicellulose ? in the cell wall of cabbage under low concentration of Cd treatment.In addition to the hemicellulose ? in the cell wall,Cd is also largely bound to pectin and cellulose under high concentration of Cd treatment.And there are significant differences between varieties.Effect of hemin on growth of cabbage under Cd Stress.The results show as follows:In the germination period experiment,compared with the control,the germination percentage and gemination energy of cabbage seedlings were not significantly affected under Cd treatment.The seedling hypocotyl length and radicle length were significantly inhibited at the germination stage.Hemin significantly alleviated the inhibition of Cd on the growth of seedlings at the germination stage in cabbages.Under Cd stress,the ROS level and MDA content of seedlings increased significantly,and the antioxidant system was disordered,resulting in oxidative damage.Under hemin+Cd treatment,antioxidant enzyme levels in seedlings of cabbages were reduced or increased to varying degrees so that the steady-state of the antioxidant system tended to be the control level,the level of ROS was significantly reduced,and the MDA content was decreased.Finally,the oxidative damage of Cd-induced seedlings in cabbages was reduced.In order to further study the effect of hemin on antioxidant enzymes in cabbage seedlings under Cd stress,real-time fluorescent quantitative PCR was used to analyze the changes of antioxidation enzyme genes.The results showed that hemin can modulate the expression of antioxidase genes at the transcriptional level and synergize with isoenzymes to ensure normal expression of different antioxidant enzyme genes,and to increase its total activity,enhance antioxidative capacity,and reduce Cd-induced oxidative stress.In the seedling stage experiment,compared with the Cd group,the growth of cabbages under the simultaneous treatment of Cd and hemin was significantly relieved and tended to control levels.Hemin can reduce the Cd content of shoots and roots in cabbages under Cd stress.At the same time,hemin can also reduce the toxicity of Cd by increasing the content of sulfhydryl contents,chelated peptides,total amino acids,organic acids and antioxidants contents in cabbages.In summary,Cd is mainly distributed in the root system to reduce its toxicity in plants,and the performance of the Cd-tolerant variety is more obvious.The fixed effect of the cabbages roots on heavy metals is mainly achieved through the structure and function of the cell wall.It shows that Niuxin is tolerant to Cd,and also shows that the regionalization of on heavy metal ions by cell wall is an important detoxification mechanism for cabbage.Hemin can effectively alleviate the toxicity of Cd on cabbages.