Effects Of Lead Stress On Physiological Characteristics Of Petunia × Hybrida

In recent years,traffic emissions,mineral mining,factory wastes,and garbage dumps,and other factors that caused soil heavy metal pollution,including Lead（Pb）will cause harm to soil,plants,and the human body.In soil,Pb is absorbed by plant roots in the form of insoluble compounds and causes certain harm to plants,leading to stunted growth and development of plants,and even death in severe cases.Therefore,it is particularly important to select the plants suitable for survival in Pb contaminated soil.Petunia×hybrida,as a green plant with strong environmental adaptability,stem leafiness,and high economic benefits,has attracted much attention from researchers in the ornamental market,but there are little researches on the tolerance to Pb pollution in petunia.Therefore,it is of great significance to select petunia to study the tolerance to Pb pollution.This study selected"the petunia and its soil in the urban area of Lanzhou"and"the petunia provided by Plant Tissue Culture Laboratory,School of Life Science and Technology,Longdong University"as experimental material,through the analysis of the pollution degree of outdoor Pb in soil,explored the ability of petunia to transfer and distribute Pb,stressed by different concentrations of Pb(0.05,0.8,1,and 2 mmol·L^-1)on the growth and photosynthesis of indoor petunia seedlings were further analyzed,and the protective effects of enzyme antioxidants and osmotic regulators on petunia seedings under oxidative stress were also discussed.The main findings were as follows:1.The soil Pb pollution index of the outdoor sampling points was 1.8.Under the stress of 0.05 and 0.8 Pb mmol·L^-1,the transport capacity of Pb was not affected by indoor petunia tissue culture seedlings.2.Except for 0.05 mmol·L^-1 Pb,other concentrations of Pb inhibited the growth of petunia seedlings,decreased the biomass and leaf area,and also significantly decreased the root-shoot ratio and root tolerance index.Under 1 and 2mmol·L^-1 Pb stress,the contents of chlorophyll and lutein in petunia decreased significantly compared with the control.The carotenoid content of petunia seedling leaves was significantly reduced under 2 mmol·L^-1 Pb stress compared with the control.The chlorophyll a/b value has no significant difference compared with the control under Pb treatment.3.Under Pb stress,the chlorophyll fluorescence parameters of petunia seedlings will change,including initial fluorescence（F₀）,Non-photochemical quenching（NPQ）,and Quantum yield of regulatory energy dissipation（Y（NPQ））increased significantly with the increase of Pb concentration;the maximum fluorescence（Fm）,variable fluorescence（Fv）,Potential activity of PSII in the light(Fv/F₀,Maximal photochemical efficiency（Fv/Fm）,Effective photochemical quantum yield（Y（II））,Photochemical efficiency of PSII In the light（Fv’/Fm’）,coefficient of photochemical quenching（q P）and Electron transport rate（ETR）decrease significantly with the increase of Pb concentration.But under low Pb(0.05mmol·L^-1)stress,these parameters were not significantly different from the control.4.Compared with the control,Pb stress can significantly reduce the stomata opening,Stomatal conductance（Gs）,(Net photosynthesis rate（A）,Transpiration rate（Tr）of petunia leaves;while the stomatal density and Intracellular CO₂ and concentration（Ci）Compared with the control,the Pb concentration increased significantly;but under low Pb(0.05 mmol·L^-1)stress,these parameters were not significantly different from the control.Besides,the water use efficiency（WUE）of petunia leaves did not change significantly with the increase of Pb concentration.In the same way,Pb stress will induce the accumulation of Reactive oxygen species（ROS）in the leaves of petunia seedlings,increase the content of Malondialdehyde（MDA）,increase the degree of membrane lipid peroxidation,and increase membrane permeability.The activity of petunia leaf Peroxidase（POD）under Pb treatment increased with the increase of the treatment concentration;while the leaf Superoxide dismutase（SOD）,Catalase（CAT）and Aseorbate peroxidase（APX）started to increase from 0.8 mmol·L^-1 Pb treatment,as the treatment concentration increases,there was an increasing trend.Under Pb stress,the content of soluble sugar in petunia leaves increased with the increase of stress,while the content of proline and soluble protein began to increase significantly with the increase of concentration under the stress of 0.8 mmol·L^-1 Pb.The above results show that the soil Pb has reached 1.8 in the natural environment.In vitro petunia seedlings,it was found that the ability of petunia to transfer Pb was not affected under 0.05 and 0.8 mmol·L^-1 Pb treatment.Furthermore,it was found that 0.05 mmol·L^-1 Pb had no significant effect on petunia growth,but0.8,1 and 2 mmol·L^-1Pb stress could inhibit petunia seedling growth,reduce its biomass,root-shoot ratio and root tolerance index.Under the stress of different concentrations of Pb,petunia will reduce the stomata opening,Gs,A,Tr,and photosynthetic pigment content by adjusting the stomata morphology of the seedling leaves,which can effectively inhibit the opening level of the PSII reaction center,thereby reducing Fv/F₀,qP and ETR,etc.,inhibit the growth of petunia seedlings.Pb treatment can also induce the accumulation of ROS in the leaves of petunia,causing the increase of MDA content,making the degree of membrane lipid oxidation serious,and then stabilizing plant oxidation by increasing the content of SOD,POD,CAT and APX,and other active and osmotic regulators.Stress balance and strengthen the adaptability of petunia to Pb.