Mitigation Effect Of Iba On Cadmium Stress In Lettuce(Lactuca Sativa L.)and Its Mechanism

Cadmium is a non-essential plant element.With the acceleration of human industrialization,cadmium pollution near cities has become more serious.Lettuce,as a vegetable planted in a wide range around the city and with a large consumption,easily accumulates cadmium and enters the human body along the food chain,which harms human health.Auxin plays an important role in plant stress resistance.As an endogenous auxin,indole-3-butyric acid(IBA),little research has been done on plant stress resistance.This study mainly explored the effects of IBA treatment on the growth of lettuce seedlings under cadmium stress,cadmium fixation in the root system,photosynthesis,absorption of mineral nutrients and antioxidant enzyme systems.The following research results were obtained:1.Appropriate concentration of IBA applied externally can effectively relieve the inhibitory effect of cadmium stress on the growth of lettuce plants,increase the absorption and accumulation of cadmium in lettuce,and increase the biomass of the aerial parts of lettuce plants under cadmium stress.The IBA concentration is 0.5 μmol/L,it had the best effect on increasing lettuce biomass under cadmium stress,and the leaves were greenest.2.IBA treatment promotes the absorption of cadmium by lettuce roots under cadmium stress,but also increases the fixation of lettuce roots to cadmium.Lettuce absorbs more cadmium by increasing the content of cell wall pectin and hemicellulose 1 to make lettuce above ground cadmium content did not increase significantly.IBA treatment can also change the chemical form of cadmium in lettuce,by reducing the ratio of lettuce root CdE,to reduce the transfer of root cadmium to the ground.3.Cadmium stress significantly reduced the growth and vigor of plant roots;disrupted the element balance in lettuce,and the shortage of elements prompted the upregulation of gene expression levels of IRT1,Nramp1 and ZIP3.IBA treatment significantly promoted root development,changed root morphology,increased biomass and number of lateral roots,increased root vitality,restored element balance in lettuce,further increased the gene expression of IRT1,Nramp1 and ZIP3,and promoted root system The absorption of nutrients makes the content of Mg,Mn and Ca in the shoot significantly increase.4.Cadmium stress severely inhibits the photosynthesis efficiency of lettuce,reduces the chlorophyll content,significantly reduces the fluorescence of OJIP,the balance of fluorescence-induced kinetic parameters is disrupted,and Rubisco enzyme activity is reduced;the heat dissipation of the photosynthetic mechanism and the amount of ring-shaped electron transfer are significantly increased.IBA treatment significantly increased the chlorophyll content of lettuce under cadmium stress,promoted the increase of the enzyme activity of Rubisco,increased the fluorescence level of OJIP,balanced the fluorescence parameters,reduced the amount of ring electron transfer of photosynthetic mechanism and increased its rate,increased the linear electron The transfer amount ultimately increased the photosynthesis efficiency of lettuce leaves under cadmium stress.5.Cadmium stress increases the oxidative stress in lettuce,increases the activity of SOD and POD,and reduces the activity of CAT and APX.IBA treatment increased the activity of CAT and POD in the shoot lettuce under cadmium stress,reduced the activity of SOD and APX in the root,and reduced the accumulation of H2O2 in lettuce leaves.In conclusion,IBA treatment absorbs more nutrients and cadmium by increasing the ability of the root to absorb ions,while fixing more cadmium in the root system,so that the cadmium content in the aerial part can be controlled,and more nutrients increase the photosynthetic efficiency and increase The activity of the antioxidant enzyme system is reduced,and the accumulation of reactive oxygen is reduced,especially the activity of the Rubisco enzyme is increased,which increases the rate of carbon assimilation,prevents the superoxide anions generated by the accumulation of excessive reducing power from damaging the photosynthetic mechanism,and finally relieves the lettuce caused by cadmium Growth is inhibited.