Effects Of ABA On Apple Fruit Ripening,Ethylene Synthesis And Signal Transduction

As one of the important hormones in plant growth and development,Abscisic acid(ABA)is widely believed to regulate ethylene biosynthesis and signal transduction during fruit ripening,but the molecular mechanism of interaction between ABA and ethylene is still unclear.As the most important climacteric fruit in China’s fruit market,apple has little research on the effects of ABA on its fruit ripening.In order to explore this problem,this article used the ‘Granny Smith’in the first month before the commercial harvesting period as the research material,and was treated with 1mL 500 μL/L ABA for intravital injection and stored at room temperature.The fruit soluble solids content(SSC),titratable acid(TA),fruit hardness,color difference,chlorophyll content,the activity of pectin methylesterase(PME)and cellulose(Cx)were analyzed after exogenous ABA treatment.Endogenous ABA content and ethylene release rate were analyzed.The expression of corresponding genes in ethylene synthesis and signal transduction pathway was analyzed by qRT-PCR.At the same time,the focus was on the changes of the transcription factor MdHB1 in ethylene synthesis.The main findings are as follows:1.Compared with the control group,exogenous ABA treatment can reduce the hardness of the fruit,and accelerate the chlorotic and yellowing of the fruit.ABA treatment can increase the activity of PME at a higher level of 84.4 %,and cause the peak of Cx activity to appear 5 days earlier,which promotes the softening of fruits in advance;exogenous ABA treatment can induce the increase of endogenous ABA content and promote fruit respiration.The increase in strength and ethylene release rate,respiratory peak and ethylene release peak appeared 5 days earlier,indicating that ABA can induce the release of ethylene from apple fruit and accelerate the ripening and softening process.2.Quantitative real-time PCR(qRT-PCR)analysis showed that exogenous ABA treatment increased the expression levels of ethylene synthesis related genes MdACO1,MdACO2,MdACS1 and MdACS3 by 2.8-fold,3.7-fold,1.8-fold,and 2.5-fold respectively;The expression of MdERS1,MdERS2,MdERF3,MdERF4,MdERF5,MdETR2,MdMPK1 and MdMPK2 in the pathway was also induced by ABA,and a higher expression was observed at the end of maturity.MdETR1 was hardly expressed during the entire storage period.This means that ABA can regulate ethylene production and ethylene-led maturation by inducing genes involved in ethylene synthesis and signal transduction in fruits.3.The expression analysis of MdHB1 transcription factor during fruit storage showed that the expression of MdHB1 was consistent with the fruit ripening process.The expression of MdHB1 was increased by 4.6 times after ABA treatment,and the expression of MdHB1 was earlier than that of ACOs,which means ABA.It plays a certain role in the process of inducing ethylene synthesis.Staining by yeast one-hybrid and GUS activity indicated that MdHB1 can bind to the promoter of MdACO1 and increase the activity of the MdACO1 promoter.This indicates that ABA may regulate the synthesis of ethylene by inducing the expression of MdHB1.