Effects Of Indole Acetic Acid And Kinetin On Physiological Response Of Helianthus Tuberosus L.under Cd Stress

With the rapid development of China’s industry,coal burning,smelting,mining and other engineering operations make a large amount of cadmium into water and soil,causing serious cadmium pollution in local areas.Phytoremediation technology can absorb and degrade pollutants in soil,water and atmosphere through absorption and transport of substances in soil by roots and through the mechanism of degradation in vivo,so as to achieve the purpose of environmental remediation.It plays a crucial role in ecological engineering.In this paper,Helianthus tuberosus L.with strong stress resistance was selected as the research object.Through analyzing the effects of indoleacetic acid（IAA）and kinetin（KT）on DNA damage,photosynthetic characteristics,antioxidant enzyme activity and osmotic regulation ability of H.tuberosus under cadmium stress,the effect and mechanism of IAA and KT on cadmium superenrichment of H.tuberosus were discussed.In order to provide theoretical support for the application of phytoremediation technology of cadmium contaminated soil under the coordination of exogenous hormone regulation.The results are as follows:1.Different concentrations of hormones have different effects on plant height and root elongation of H.tuberosus under cadmium stress.Lower concentrations of IAA and KT can promote the growth of H.tuberosus,while higher concentrations can inhibit it.When IAA concentration was 4mg/L,the plant height and root elongation of H.tuberosus from secondary producing area were the highest,which were 39.83%and 25.52%for Chengdu and 34.96%and 43.06%for Yulin H.tuberosus.Under 8mg/L KT treatment,the plant height elongation of Chengdu H.tuberosus was significantly increased by17.44%-37.38%（P<0.05）,and the root elongation was increased by 29.93-40.27%.There was no significant difference in plant height and root elongation among different treatment groups（P>0.05）,but the maximum was reached at 8mg/L KT concentration.To sum up,4mg/L IAA and 8mg/L KT were selected to carry out the next comparative experiment.2.Under cadmium stress,the chlorophyll structure of H.tuberosus was damaged,the chlorophyll content decreased significantly（P<0.05）,the net photosynthetic rate（Net Photosynthetic Rate,Pn）,stomatal conductance（Stomatal Conductance,Gs）and transpiration rate（Transpiration Rate,Tr）decreased,and the intercellular CO₂concentration（Intercellular CO₂Concentration,Ci）increased.The electron transfer rate（Electron Transfer Rate,ETR）,the initial fluorescence（Initial Fluorescence,F_o）and the maximum light energy conversion efficiency（Maximum Light Energy Conversion Efficiency,Fv/Fm）of PSII were significantly decreased（P<0.05）,the photochemical quenching coefficient（Photochemical Quenching Coefficient,q P）was not significantly changed,but the non-photochemical quenching coefficient（Non-Photochemical Quenching Coefficient,q N）was significantly increased（P<0.05）.IAA and KT significantly increased（P<0.05）chlorophyll content,and F₀,Fv/Fm,ETR and q N recovered to the level of CK group,Pn,Gs and Tr increased,while Ci decreased.These results indicated that IAA and KT could effectively alleviate the damage of photosynthesis caused by cadmium stress and ensure the nutrient absorption and accumulation of H.tuberosus.3.Under cadmium stress,the activities of superoxide dismutase（SOD）,peroxidase（POD）and catalase（CAT）of H.tuberosus decreased,while the contents of MDA,proline,soluble sugar and soluble protein increased first and then decreased,indicating that cadmium induced membrane lipid peroxidation of H.tuberosus and damaged its antioxidant system.Maintain osmotic pressure inside and outside the cell,reduce MDA accumulation.IAA and KT can significantly improve the activities of three antioxidant enzymes and the content of osmotic regulatory substances,alleviate the damage of membrane lipid peroxidation,and ensure the integrity of cell membrane.4.DNA damage test results under cadmium contamination,under cadmium stress,the comet head of H.tuberosus appeared long and bright tail,comet tail length（Tail Length,TL）,COMET tail DNA content（Tail DNA,TD）,tail moment（Tail Moment,TM）and Olive tail moment（Olive Tail Moment,OTM）all showed an increasing trend.DNA damage was serious,resulting in a large number of DNA broken strands and fragments.After IAA and KT treatment,the DNA damage of H.tuberosus was alleviated.The OTM of IAA group,KT group and IAA+KT group was significantly lower than that of IAA group,suggesting that KT had an excellent alleviating effect on DNA damage caused by cadmium stress.When IAA and KT were used together,there was no significant difference between the comet pattern and CK group,and DNA damage was repaired.5.Determination of heavy metal content in organs and soil of H.tuberosus.The content of Cd in each tissue of H.tuberosus was root>stem>leaf.The content of Fe in the root,stem and leaf of H.tuberosus was leaf>stem>root,contrary to the content of Cd,imply Cd mainly entered cells through Fe transporter.IAA significantly increased the transport coefficient of H.tuberosus,and KT significantly increased the enrichment coefficient of H.tuberosus.The combined application of the two factors could help H.tuberosus efficiently repair cadmium contaminated land.