Study On The Effects And Mechanisms Of Gibberellin On Alleviating Cadmium Stress In Lettuce(Lactuca Sativa L.)

In recent years,heavy metal pollution in farmland is serious,which has been widely concerned.Cadmium is a non-essential element of plants,but because of its high solubility and fluidity,its chemical form is similar to the essential mineral elements of plants,which can be easily absorbed and accumulated by plants,damaging plant growth and entering the human body along the food chain,posing a threat to human health.Gibberellin is a classical plant hormone and plays an important role in plant growth.Many studies have reported that gibberellin promotes seed germination and growth and development,and also plays a certain role in many abiotic stresses,and can alleviate the toxic effects of cadmium on Guayule,Wheat,Arabidopsis and other plants.However,the mechanism of gibberellin alleviating cadmium stress in lettuce is not clear.This paper mainly explored the alleviating effect of gibberellin on cadmium stress in lettuce and its mechanism.The main results are as follows:1.Different concentration of gibberellin(1、5、10μM)could promote the growth of lettuce,and increase the biomass of lettuce under cadmium stress,reduce the cadmium content of the shoot of lettuce,and alleviate the stress caused by cadmium on lettuce.This kind of alleviating effect has a certain concentration dependence,when the leaf surface spraying gibberellin concentration is 10 μM,it has the best effect on reducing the cadmium content of the shoot of lettuce under the stress of cadmium.2.Gibberellin affect the lettuce plants root-shoot ratio,promote the growth of lettuce above ground,and increase the lettuce plant height,leaf number and leaf area,increase the lettuce above ground biomass,so as to alleviate the toxicity of cadmium on lettuce.From the perspective of the root of lettuce,gibberellin can affect the lettuce under cadmium stress by change of root morphology,increase root activity and antioxidant enzyme activity of root to alleviate the effects of cadmium on lettuce.3.Gibberellin can reduce the content of cadmium in the lettuce,reduce the translocation factor of cadmium in lettuce,save cadmium in root,inhibit the transport of cadmium to the shoot,and alleviate the cadmium stress on lettuce.But cadmium subcellular distribution experiment found that gibberellin does not change the distribution of cadmium in cell components,the gibberellin path to mitigation cadmium stress on lettuce is not this way.Cadmium accumulation in the root of lettuce after gibberellin treatment may be caused by affecting the root-shoot ratio of lettuce and reducing the biomass of the root on lettuce.4.Gibberellin also inhibits the expression of IRT1 and Nramp1 to reduce the cadmium uptake of lettuce.At the same time,the expression of HMA2 and HMA4 was inhibited,so that the transport of cadmium from root to shoot was reduced.The decreased expression of the HMA3 located in the vacuolar membrane also confirmed that gibberellin alleviates cadmium stress on lettuce did not result from the vacuolar regionalization.And gibberellin can restore the balance of some cadmium on the mineral element absorption of lettuce.5.Gibberellin alleviate cadmium stress on the lettuce is not achieved through photosynthesis,the cadmium and gibberellin made lettuce plants photosynthesis decline of per unit leaf area,but as a result of gibberellin can make lettuce plant leaf area,leaf number,and the biomass increased,the photosynthesis decline of per unit leaf area does not affect the whole of the lettuce plants photosynthesis.6.The application of gibberellin on leaves did not reduce the nutritional quality of lettuce.It has certain inhibitory effect on the decrease of lettuce vitamin C under cadmium stress,so it is feasible to promote the production and application.These results showed that the main mechanism of leaf surface application of gibberellin to alleviate cadmium stress in lettuce are as follows:change the root-shoot ratio of lettuce,promote the growth of lettuce,increase the lettuce shoot biomass,leaf area,leaf number,change the root morphology of lettuce,improve activity of antioxidant enzymes in root,reducing cadmium peroxidation damage of lettuce roots;IR T1,Nramp1,HMA2.and HMA4 expression were suppressed to reduce cadmium uptake and transport to the shoot of lettuce,so as to maintain the balance of some mineral elements in lettuce under cadmium stress.Foliar application of gibberellin of 10 μM was most effective.