镉胁迫下施硒对冬小麦幼苗镉吸收、抗氧化能力及植株超微结构的影响

Effects of selenium application on cadmium uptake,antioxidant activity,and ultrastructure of winter wheat seedlings under cadmium stress

【目的】硒(Se)在提高植物抗逆性方面起着重要作用。硒减轻植物重金属Cd毒害的直接和间接机制需要进一步研究。【方法】供试作物为小麦(Triticum aestivum L.)。水培试验设置5个处理:Hoagland基础营养液(CK),营养液中只添加Cd 5μmol/L(Cd5Se0),添加Cd 5μmol/L和Se 5μmol/L(Cd5Se5),只添加Cd 20μmol/L(Cd20Se0),同时添加Cd 20μmol/L和Se 5μmol/L(Cd20Se5)。通过测定小麦镉含量和抗氧化系统相关指标,研究硒对小麦镉吸收时间动力学的影响以及小麦抗氧化体系中的调控机制;并观察了叶片和根系细胞的超微结构。【结果】镉胁迫下,施硒使小麦地上部的镉含量降低了18.20%~38.16%,镉积累量显著降低了40.79%~43.05%(P<0.05)。小麦根系在0~24 h内对镉的吸收特征符合一元二次方程,24 h内,在Cd5和Cd20条件下,施硒后小麦对镉的吸收量分别降低了48.96%和11.47%。相较于CK,在Cd20条件下,根和叶片中超氧阴离子(O_(2)^(-))的产生速率以及过氧化氢(H_(2)O_(2))和丙二醛(MDA)的含量显著增加,超氧化物歧化酶(SOD)、过氧化物酶(POD)活性和抗坏血酸(ASA)含量显著增加,抗坏血酸过氧化物酶(APX)活性显著降低(P<0.05)。不同镉水平下,施硒使小麦根中H_(2)O_(2)含量显著降低了34.21%~50.32%,叶片MDA含量降低了10.34%~24.91%(P<0.05),叶片APX活性显著提高了29.09%~30.46%(P<0.05),SOD和POD活性恢复到对照水平。镉胁迫下,小麦植株中细胞器均遭到不同程度破坏,施硒的小麦细胞器的损害得到一定的缓解。【结论】施硒降低了镉胁迫下冬小麦地上部和根部的Cd含量与积累量,降低了镉的最大吸收量和积累量,增强了小麦幼苗抗氧化的能力,减轻了由于镉胁迫造成的小麦根系和叶片细胞超微结构的损伤,进而缓解了镉对小麦幼苗的毒害。

【Objectives】Selenium(Se)plays an important role in improving plant stress resistance.We studied the direct and indirect mechanisms of selenium alleviating the toxicity of heavy metal–cadmium in plants,which needs further study.【Methods】The test method was hydroponic experiment,and the test crop was wheat(Triticum aestivum L.).The treatments included Hoagland basal nutrient solution(CK),Cd 5μmol/L(Cd5Se0),Cd 5μmol/L and Se 5μmol/L(Cd5Se5),Cd 20μmol/L(Cd20Se0),and Cd 20μmol/L and Se 5μmol/L(Cd20Se5).The total Cd content,kinetics of Cd absorption,and the activity of antioxidant enzymes of wheat seedlings were determined,and the ultrastructure of leaf and root cells was observed.【Results】Under Cd stress,Se application reduced the Cd content in the aboveground part of wheat by 18.20%−38.16%,and significantly reduced Cd accumulation by 40.79%−43.05%.The dynamics of wheat root Cd absorption in 0−24 h conformed with the quadratic equation.Under Cd5 and Cd20 condition,Se application decreased Cd absorption within 24 h by 48.96%and 11.47%,respectively.Compared with CK,Cd20 markedly increased the O_(2)^(-)production rate,H_(2)O_(2)and malondialdehyde(MDA)content in wheat roots and leaves,increased the activities of superoxide dismutase(SOD),peroxidase(POD)and the content of ascorbic acid,and decreased the activity of ascorbic acid peroxidase(APX)significantly.While Se application significantly reduced the content of H_(2)O_(2)in roots by 34.21%−50.32%,MDA content in leaves by 10.34%−24.91%,it increased the activity of APX in leaves by 29.09%−30.46%and restored the activities of SOD and POD to the control level.The organelles in wheat under Cd stress were damaged at varying degrees,and were alleviated under Se application.【Conclusions】Under Cd stress,Se application reduced the content and accumulation of Cd in aboveground part and root of winter wheat,reduced the maximum absorption and accumulation of Cd,enhanced the antioxidant capacity of wheat seedlings,thus alleviated the damage of ultrastructure of wheat root and leaf cells due to Cd stress,and alleviated the toxicity of Cd in wheat seedlings.