The Mechanism Of Oxidative Damage To Maize Radicle Induced By The Volatile Oil From Chenopodium Ambrosioides L.

Allelopathy is one of the main mechanisms of successful invasion of Chenopodium ambrosioides L.. The volatile oil of C.ambrosioides can induce cell oxidative damage. In order to reveal the cellular and molecular mechanism of oxidative damage to the plant induced by C. ambrosioides. After clarified the main ingredients of the volatile oil, the volatile oil and its two main ingredients, α-terpinene and the cymene, were chosed as the donors. And Zea mays L., the crop which widely planted in the field where C.ambrosioides is growing, was chosed as the receptor plant. The accumulation of reactive oxygen in the radicle and the extent of the damage induced by the donors were investigated; The activities and gene expressions of the antioxidant enzymes, such as superoxide dismutase（SOD）, peroxidase（POD） and catalase（CAT）, were determined; Then the concentrated areas of Ca²⁺ in the radicle and the relief effect by the exogenous antioxidants were also studied. The allelopathic mechanism of the oxidative damage induced by C.ambrosioides to maize radicles was explored using biochemical analysis, ROS staining, Ca²⁺ staining and RT-q PCR. We can conclude as follows.（1） The growth of maize radicle and the root length were inhibited significantly. Compaed to the allelopathic effect index, the volatile oil of the stress effect is the most obvious（0.53）, followed by the α-terpinene（0.49）, and the cymene was the weakest（0.46）.（2） Activities of the three kinds of antioxidant enzymes was suppressed in the role, and they were negatively correlated with treatment dose and treatment time. And the inhibiting effect on SOD activity was the most significant. The influence to antioxidant enzymes activities by α-terpinene was more obvious than cymene. Isoenzymezymogram analysis showed that POD and SOD isozyme bands reduced with the increase of treatment time and treatment dose, and the band color become pale, the brightness become darksome. CAT isozyme bands disappeared in high dose and long time treatment. RT-q PCR analysis showed that the expressions of SOD gene（Zm SOD） and POD gene（Zm POD） of maize radicle were down-regulated. And the expression of the CAT gene（Zm CAT） was up-regulated significantly with the increasing treatment dose under the stress induced by the volatile oil and cymene, while was down-regulated by α-terpinene. Overall, the changes of antioxidant enzyme activities and its gene expression have significant correlation.（3） The accumulation of reactive oxygen species also raised with the increase of treatment dose. The contents of MDA and ROS in the tip cells induced by the increasing treatment doses, and the production area of ROS mainly distributed in root cap and meristem area. And the Ca²⁺ were gathered in root tip meristematic zone, too. Exogenous As A remitted the inhibitive effect to the antioxidant enzyme activities induced by the stress of C. ambrosioides. At the same time, the accumulation of ROS also reduced after applying As A. The mitigative effect was more significantly increased with the increasing concentration of As A. In conclusion, the volatile oil from C. ambrosioides and its two main components induced oxidative damage to maize root tip cells, lead to membrane lipid peroxidation and membrane permeability increased, Ca²⁺ concentrated in the cytoplasm, and trigger the apoptosis pathway. Compared with cymene, the allelopathic effect of α-terpinene is more apparent.In conclusion, the activities of antioxidant enzymes and their gene expressions were down-regulated when treated by the volatile oil or its two main components. And the expression of antioxidant enzyme profile was changed. The accumulation of ROS and membrane lipid peroxidation and membrane permeability increased and extracellular Ca²⁺ internal flow. The volatile oil and its two main components induced oxidative damage, and triggered the program of apoptosis; Analysis of the comprehensive effect showed that the stress to the antioxidant system of maize radicle of the volatile oil was the most obvious（0.413）, followed by α-terpinene（0.398）, cymene was the weakest（0.325）.