Analysis Of The Factors Affecting The Volume Development Of Orange Fruit

Fruit size is an important agronomic trait of fruit.It is not only an important index to measure the appearance quality of fruit products,but also has an impact on consumer acceptance and price,and affects the yield of fruit trees to a great extent.In this study,using large fruit variety ‘Daguo Jincheng'(Citrus sinensis L.Osbeck cv.Daguo Jincheng)and small fruit variety ‘Changyecheng'(C.sinensis L.Osbeck cv.Changyecheng)both mutated from Jiangjin sweet orange seedling populations as materials,from cytology,physiology and molecular biology,to study the mechanisms of citrus fruit volume development,the results can lay a foundation for the research of further understanding of molecular and physiological mechanism of citrus fruit volume growth and molecular genetic breeding.The main results of this paper are as follows.1.The study on development of Daguo Jincheng and Changyecheng suggest that the fruit diameter of longitudinal and transverse development showed a double S type dynamic change.215 days after flower the fruit size dose not increase,the fruit diameter of longitudinal and transverse of Daguo Jincheng were significantly higher than that of Changyecheng,the fruit shape index of Changyecheng is less than 1 and is more than 1 of Dagguo Jincheng.Using the method of paraffin section to observe the two varieties' s cell number and size in the period of cell division,the results showed that the cell number and cell size of Daguo Jincheng were significantly higher than of Changyecheng.Determined the AGR and RGR in the stage of fruit enlargement indicate that the AGR and RGR of Daguo Jincheng were significantly higher than of Changyecheng.2.The endogenous hormones content of IAA,ZT,GA3 of the two cultivars in different development stages were determined by high performance liquid chromatography.The results showed that: in the pericarp tissue,the content of IAA,ZT and GA3 of Daguo Jincheng were higher than those of Changyecheng in the period of fruit cell division,In Daguo Jincheng the IAA and GA3 content were higher and ZT were lower than those of Changyecheng,in the pulp tissues,the IAA content of Daguo Jincheng was higher than that of Changyecheng,the ABA content was lower than that of Changyecheng,the content of ZT and GA3 were no significant between the two varieties.In the fruit cell division and expanding stages,the IAA/ABA and GA3/ABA of Daguo Jincheng were higher than that of Changyecheng.The significant differences in the contents of endogenous hormones may be one of the reason for the fruit size of Daguo Jincheng is bigger than that of Changyecheng.Use exogenous hormone treat the young fruit suggest that daub GA3 and ABA on young fruit in division stage and daub GA3,IAA,ABA in expanding stage can significantly increase fruit size,in the division phase of exogenous hormone treatment has a greater impact on fruit size.3.During the fruit development,the expression of 15 auxin synthesis genes(CsYUC),9 abscisic acid synthesis genes(CsNCED)and 4 gibberellin synthesis gene(CsGAox20)were determined by Real time PCR.The results showed that the expression of CsYUC6 and CsYUC7 in Daguo Jincheng is significantly higer than that in Changyecheng,and the contemporaneous IAA content of Daguo Jincheng was higher than that of Changyecheng,suggest that CsYUC6 and CsYUC7 may play an important role in fruit auxin synthesis process.The expression of CsNCED3 of Daguo Jincheng in fruit peel tissues is significantly higher than that of Changyecheng,in the flesh tissue is lower than that of Changyecheng,the expression of CsNCED8 in fruit peel and flesh of Daguo Jincheng is lower than that of Changyecheng,at the same period the difference of ABA content in the two varieties can be inferred that CsNCED3 and CsNCED8 may play an important role in the synthesis process of ABA.The expression of CsGAox20-2 of Daguo Jincheng in is higher than that of Changyecheng,and the contemporaneous GA3 content of Daguo Jincheng was higher than that of Changyecheng indicating that CsGAox20-2 may play an important role in the gibberellin synthesis process.To sum up,it can be inferred that the hormone synthesis genes may affect the development of fruit by regulating the synthesis of related hormones.In summary,the differences of fruit cell number and size is the cytological basis reason caused the differences of fruit size between Daguo Jincheng and Changyecheng.The high expression of CsYUC6,CsYUC7,CsGAox20-2 and low expression of CsNCED3,CsNCED8 in Daguo Jincheng,leading to high content of IAA,GA3 and higher IAA/ABA,GA3/ABA ratio than that in Changyecheng,the above factors constitute the molecular basis of that the fruit size of Daguo Jincheng is bigger than Changyecheng.