| Apples are one of the most widely cultivated fruits in China,and salinized soils are a serious constraint to the development of apple farming.The root system is the "root" of the plant,and high salt stress inhibits root growth.Dopamine is involved in stress regulation of plant carbon metabolismto reduce the damage of salt stress and promote normal plant growth.Nowadays,there are few studies on the effect of dopamine on apple root growth to mitigate salt stress.In this experiment,we used ’Gala’ as the test material to study different concentrations of dopamine to alleviate the root damage of apple seedlings and to screen the optimum concentration of dopamine to alleviate root growth.The effect of dopamine on the alleviation of adventitious root development in apple seedlings grown under salt stress was investigated,and then the relationship between dopamine and physiological and biochemical indicators in adventitious root development was further analyzed.To provide a theoretical basis for the application of dopamine to the study of salt resistance in apples,thus provide technical support for the growth and development of apples in salt-stressed environments.The results of the study were as follows:1.The root growth of ’Gala’ was inhibited by 0.45% Na Cl,exogenous application of different concentrations of dopamine increased chlorophyll content,root vigor,soluble protein content,SOD,POD,and CAT activities,and root length,projected area,surface area,volume,and mean diameter in apple seedlings.Among them,root application of 50 μmol/L dopamine significantly promoted root growth,increased root vigor and soluble protein content,and increased SOD activity by 1.8 times,POD activity by 2.0 times,and CAT activity by 3.4times.The optimum concentration of dopamine on the root system of apple seedlings under salt stress was 50 μmol/L.This indicated that the appropriate concentration of dopamine could alleviate the root damage,reduce the inhibitory effect of salt stress on apple seedlings,and improve the salt tolerance of apple seedlings.2.50 mmol/L Na Cl inhibited the occurrence of adventitious roots of ’Gala’,reduced the number of adventitious roots,and slowed down the elongation of adventitious roots.The soluble protein content decreased,soluble sugar content increased,SOD and POD activities increased,and CAT,PPO,and IAAO activities increased in 200 μmol/L dopamine treatment.The rooting rate of 200 μmol/L dopamine treatment increased by 31.6%,the number and length of adventitious roots increased by 2.95 times and 2.5 times,respectively.Therefore,salt stress significantly inhibited adventitious root development during rooting of apple tissue culture seedlings,and the addition of 200 μmol/L dopamine alleviated the inhibition of adventitious root development by salt stress,thus increasing the rooting rate of apple tissue culture seedlings.3.50 mmol/L Na Cl affected the expression of genes of the growth hormone signaling pathway and genes related to root development at the adventitious root formation stage of’Gala’.The three treatment groups,control,salt stress and dopamine,showed the highest gene expression at adventitious root onset.200 μmol/L dopamine treatment promoted the expression of Md ARF7,Md ARF19,Md ARF22,Md IAA3,Md IAA14,Md IAA23,Md LBD16,Md LBD29,Md WOX5 and Md WOX11 in different developmental stages.Combined with the rooting situation,it was speculated that dopamine alleviated the effects of salt stress on plants and increased the rooting rate of apple tissue culture seedlings,probably due to exogenous dopamine promoting or inhibiting the synthesis of endogenous IAA hormones,which influenced the occurrence of adventitious roots and thus induced root development and the expression of growth hormone-related genes. |
