Preliminary Study On The Response Mechanism Of Three Plant Growth Regulators To Radish Growth And Salt Stress

Raphanus sativus L.is a plant of the genus Radish in the Cruciferous family.Its product organs are plump fleshy roots,which have important nutritional,economic and medicinal values and are cultivated throughout China.In the production of radish,improving the growth of succulent radish root is very important for the yield and quality of radish.And radish production will inevitably suffer from the harm of salt stress,thus affecting its growth and development,resulting in a large number of economic losses.Indoleacetic acid(IAA),Melatonin(MT)and 2,4-Epibrassinolide(EBR)are three common plant growth regulators in agricultural production.It plays an important role in regulating plant growth and development and stress tolerance.In this study,radish was used as material,and hydroponic method was adopted to carry out two parts of the experiment.In the first part,three radish varieties(Rs1,Rs2,Rs3)were treated with different IAA concentrations(10,20,25 and 50 μmol/L),MT concentrations(10,50,100 and 200 μmol/L),and EBR concentrations(0.05,0.1,0.5 and 1 mg/L),and determine the growth indexes after different treatment times.The purpose of this study was to screen out the optimal concentrations of IAA,MT and EBR for radish growth,and determine a series of physiological and biochemical indexes at the same time,to explore the effects of different concentrations of IAA,MT and EBR on the physiological and biochemical indexes of radish fleshy roots.The second part is about the regulatory mechanism of exogenous IAA,MT and EBR on the growth and development of radish under salt stress.There are 5 treatments(CK,Na Cl,Na Cl+IAA,Na Cl+MT and Na Cl+EBR),wherein CK is nutrient solution treatment with Na Cl concentration of 150 mmol/L.The concentration of IAA,MT and EBR was selected as the optimal concentration in the first part.To study the effects of exogenous IAA,MT and EBR treatment on the growth of radish under salt stress,the growth indexes and physiological and biochemical indexes of radish under different treatment time were measured.The test results are as follows:1.Different concentrations of autin(IAA)inhibited the shoot fresh weight and root length of Rs1,and 50 μmol/L IAA inhibited the leaf length and leaf width of the three radish varieties.IAA treatment at the concentration of 10 μmol/L promoted the root fresh weight and root diameter of three radish varieties.2.The growth indexes of radish were promoted at low levels but inhibited at high levels of melatonin.Especially,10 μmol/L melatonin had significant promoting effect on the growth indexes of radish Rs1 and Rs2.However,50 μmol/L melatonin treatment had no significant difference,compared with the control.While 100 and 200 μmol/L melatonin significantly inhibited the growth indexes.The effects of 50 μmol/L melatonin on the growth indexes of radish Rs3 were not significantly different from that of the control,and the growth indexes were significantly inhibited by the other concentrations.3.2,4-Epbrassinolide(EBR)could promote the fresh weight of shoot and root of three radish varieties after 30 d of treatments,and the promoting effects became more obvious with the increase of concentration.The best promoting effect was obtained under 0.5mg/L EBR.The root length and diameter of Rs2 and Rs3 were promoted by0.5 mg/L EBR treatment.2,4-epbrassinolide treatments had no significant effect on leaf length and leaf width of the three radish varieties.The morphological indexes of the three radish varieties showed extremely significant positive correlation.Taking “root fresh weight” as the correlation index of IAA,MT and EBR for screening the optimal radish growth,the optimal concentrations of IAA,MT and EBR were 10 μmol/L,10 μmol/L and 0.5 mg/L.4.During the growth of radish,the three plant growth regulators had different effects on SOD and POD activities,soluble sugar,soluble protein and MDA contents in the fleshy roots of radish.IAA treatment had no significant effect on POD activity in the early stage,but higher concentrations of 25 μmol/L and 50 μmol/L IAA significantly increased the activities of SOD under those treatments after 25 and 30 d.At the treatments of MT in this study,POD activities in radish fleshy roots increased significantly.The POD activities were promoted by low concentration of EBR,but inhibited by high concentration EBR.Three plant growth regulators of IAA,MT and EBR,could increase the contents of soluble protein and soluble sugar.IAA treatment had a slight effect on MDA content in the early stage.However,the MDA content in the middle and late stages of treatments increased with the increase of IAA concentration.Low concentration MT had no significant effect on MDA content,but high concentration MT significantly promoted the MDA content.MDA content in radish fleshy roots could increase by EBR treatment.5.Under Na Cl stress,the growth of aboveground fresh weight,root fresh weight,root diameter,leaf length and leaf width of radish were inhibited by measuring growth indicators.Compared with Na Cl stress along,Na Cl+IAA,Na Cl+MT,Na Cl+EBR treatments siginifightly increased the root freash weight of radish.Under Na Cl stress,SOD and POD activities,proline and MDA contents in radish leaves were signifightly increased.soluble sugar and soluble protein contents in radish were increased under Na Cl treatment,but the difference was not significant.After the supplementary application of IAA,MT and EBR,the activities of SOD and POD,contents of proline,soluble sugar and soluble protein were significantly increased,and the content of MDA was significantly decreased.In conclusion,exogenous treatments of 10 μmol/L IAA,10 μmol/L MT and 0.5 mg/L EBR can alleviate the damage of salt stress on radish growth.