Study On The Toxicity Mechanisms Of Different Forms Of Antimony On Rice Plants

Antimony?Sb?extensively distributes in the environment and excess of Sb is harmful to humans and plants.In recent years,the issues of Sb pollution in soil environment in China's have increasingly attracted people's attention.Rice plant is an important food crop in China,and can easily enrich a large amount of Sb.Many media reports have shown increasing incidents of Sb pollution in the grains of rice plants.Therefore,it seems to be vital to investigate the mechanisms on the toxicity,uptake,translocation and speciation transformation of different forms of antimony?Sb?in plants,which can give the theory supporting for dealing with the excess accumulation of Sb in rice grains.In this paper,we conducted three related experiments in hydroponic culture system using a rice variation named Yoshihikari No.3 to resolve below questions:1)the effects of different forms of Sb[Sb???and Sb???]on the growth of rice plants and root morphology changes;2)the effects of Sb???and Sb???on the uptake,translocation and subcellular distribution of Sb and essential elements;3)the transformation of different forms of Sb in different tissues of rice plants;4)the production of bleeding sap and the concentrations of its containing elements;5)the responses of antioxidative systems to different forms of Sb;6)the roles of root exudates,components of root cell wall and endogenous hormones in alleviating the toxicity of different forms of Sb.The main results are as follows:?1?The effects of different forms of Sb on the growth of rice plants and on the root development were studied.The results shows that the effects of different forms of Sb on the the growth of rice plants and on the root development are different.The toxicity of Sb?III?is higher than that of Sb?V?,showing as the lower biomass of shoots and roots of rice plants exposing to Sb???than exposing to Sb?V?;The addition of 20 mg·L^-1 Sb???inhibited the most of tested parameters of root morphology including root length,root volume,root surface area,root tips and root forks;however,20 mg·L^-1 Sb?V?only significantly reduced the root surface area,root diameter and root forks.The treatments containing Sb?III?increased the proportions of coarse and medium roots,but reduced the fine root proportion;however,the addition of Sb?V?reduced the coarse and medium root proportions but increased the fine root proportion.?2?The effects of different forms of Sb on the uptake,translocation and subcellular distribution of Sb and essential elements were studied.The speciation transformation of Sb in different tissues of rice plants was also monitored.The results shows that:1)the rice plants show a stronger ability to take up Sb upon exposure to Sb?III?than upon exposure to Sb?V?.The rice plants do not have a strong ability to translocate the absorbed Sb from the roots to shoots,and most Sb in rice plants are concented in the roots of rice plants;2)Sb?III?is the main speciation when the plants is subjected to Sb?III?exposure,but Sb?V?is the main speciation under Sb?V?stress,suggesting a weak ability of rice plants to transform different forms of Sb;3)in most cases the addition of Sb?III?sigficantly increased the concentrations of some essential elements in the shoots of rice plants,including Mg,K,Ca,Fe,Cu and Zn.However,only 10 mg·L^-1 Sb?V?significantly enhanced the uptake of Mg,K,Ca,Mn,Fe and Cu in the shoots of rice plants exposing to Sb?V?;4)the addition of Sb?V?significantly enhanced the production of bleeding saps with increased Fe and Cu concentrations and a decreased Ca concentration;However Sb???showed a limited effect on the production of bleeding saps but increased the Fe,Cu and Sb concentrations and a decreased the Ca concentration in the bleeding saps;5)the cell wall and cell cytosol sequested most of Sb in the shoots and roots,suggesting the important roles of them in inhibiting Sb uptake.Under Sb?III?exposure,the ability of cell wall and cell cytosol to restrain Sb became weak along with the increasing Sb exposing levels.However,the cell wall play an increasingly role in constraining the Sb when plants were subjected to Sb?V?.The addition of Sb?III?and Sb?V?resulted in more translocations of Mg,K,Fe,Zn and Cu from other subcellular components to cell organelles,and more accumulation of Ca in cell wall,suggesting the important roles of these elements in alleviating the toxicity of different Sb.?3?The responses of antioxidative systems to the stress of different forms of Sb stress was studied.The results show that:1)the addition of different forms of Sb both produced oxidative stress to rice plants,significantly enhancing the contents of MDA in the shoots and roots.The Sb???showed a higher ability to increase the content of MDA than Sb?V?;2)the enzymes like SOD and APX were activated,showing a potential role in controlling the ROS;however,most treatment containing Sb???and Sb?V?significantly reduced the activity of POD enzyme,indicating a limited role in quenching the H2O2.?4?The effects of different forms of Sb on the concentrations of cell wall components,root exudates and endogenous hormones were also evaluated.The results show that:1)the addition of different fornms of Sb significantly increased the contents of pectin and lignin,but did not significantly affect the contents of hemicelluloses I and hemicelluloses II in the roots of rice plants.Above results indicate that pectin and lignin of rice root cell wall might play roles in restraining Sb uptake;2)the concentration of oxalic acid was significantly enhanced by Sb???and Sb?V?,but the concentrations of formic acid and acetic acid were significantly decreased by Sb???and Sb???.Above results suggested that oxalic acid might play a role in regulate the uptake of Sb.3)The addition of Sb?III?significantly stimulated the formation of abscisic acid?ABA?but Sb?V?showed a non-significant effects on it,indicating the involvement of the large formation of ABA in cell senescence under Sb???treatment.The addition of different forms of Sb did not significantly affect the content of salicylic?SA?despite that there were non-significant increases in its content when subjected to different forms of Sb.Above results might indicate that the SA has a limited role in alleviating the stress of different forms of Sb.