Effect Of NAA Spraying On The Physiological Characteristics Of Flower Bud Development And Related Gene Expression In 'Nagafu No.2' Apple

In recent years,there have been many studies on the regulation of flower bud differentiation by exogenous hormones.Spraying exogenous hormones is considered to alleviate some of the difficulties in flower bud development of Fuji apple.NAA is an exogenous phytohormone of apple,It has been reported that the application of NAA in the appropriate period can increase the flowering in the second year,but the mechanism of the effect of specific NAA on flower formation has not been reported.In order to study the effect of NAA on flowering of�Nagafu No.2'apple,20 mg/L NAA was sprayed at the flowering stage and 30 DAF after flowering.The contents of endogenous hormones?ABA,GA₃,IAA,ZT??C/N?soluble sugar?sucrose,fructose?and transcriptional differences of related genes were measured terminal buds on spurs after spraying.The second year flowering rate were also investigated.The results showed that:?1?The second year flowering rate of�Nagafu No.2'apple treated with 20 mg/L NAA was significantly higher than that of the control.?2?The levels of ABA and ZT were significantly higher than those of the control and the levels of IAA and GA₃ were significantly lower than those of the control.The transcription of the treatment group MdGA20ox?the oxidase gene related to GA₃ synthesis?was significantly down-regulated compared to the control,and MdNCED₃?the gene related to ABA signaling?was highly expressed compared to the control.MdARF2?auxin response factor?and MdAFB3?an important gene for the auxin signaling pathway?were significantly down-regulated compared to control.?3?The total carbon content of in the terminal buds increased,the total nitrogen content decreased,and C/N is significantly higher than the control.The content of sucrose and fructose in the treated shoots was significantly increased compared with the control.The treated sucrose and fructose content increased significantly compared to the control,and the expression of MdSUT1?sucrose-related?and MdHXK1?fructose-related?related to sugar signal was also significantly up-regulated.?4?Expression of the flower-promoting genes MdFD,MdFT,MdSOC1 and MdLFY was up-regulated by NAA;The expression of the inhibitory gene MdFLC was significantly down-regulatedIn summary,after 20 mg/L NAA treatment,the flowering rate increased in the second year.Endogenous hormone response changes,the expression of related genes is affected,the content of endogenous hormones changes,and the dynamic balance of endogenous hormones is changed;The C/N in the source leaves increased,and the soluble sugar in the buds increased;the expression of the flower-promoting gene was up-regulated and the expression of the flower-suppressing gene was down-regulated,which was beneficial to flowering.