柑橘砧木对砂糖橘果实糖积累的影响

摘要

【目的】分析不同砧木对砂糖橘果实糖积累、相关酶活性与基因表达水平的影响，以及激素在其中发挥的作用，揭示不同砧木影响砂糖橘果实糖积累的生理与分子机制，为生产上柑橘砧木的使用提供理论依据。【方法】以砂糖橘为接穗，枳壳和红黎檬为砧木，测定果实成熟过程中糖含量及蔗糖代谢相关酶活性变化，并利用实时荧光定量 PCR对蔗糖代谢相关酶及蔗糖转运蛋白的基因表达模式进行分析；同时测定果实中脱落酸（ABA）水平和ABA生物合成中的限速酶9-顺式-环氧类胡萝卜素双加氧酶（NCED）的基因表达变化。【结果】砂糖橘果皮以积累还原糖为主，而果肉以积累蔗糖为主。在果实成熟期，枳壳砧砂糖橘果皮和果肉中可溶性总糖及蔗糖含量皆显著高于红黎檬砧的。枳壳砧砂糖橘果实中蔗糖合成酶（SS）活性更高。荧光定量PCR分析显示，在成熟期枳壳砧砂糖橘果皮与果肉中蔗糖合成酶基因SS2的表达量显著高于红黎檬砧的，而酸性转化酶基因CWINV1表达明显低于红黎檬砧的，且CWINV1表达量与蔗糖积累呈显著负相关（r=-0.648*）。同时，果皮与果肉中蔗糖转运蛋白基因SUC3表达随果实成熟呈上升趋势，且与可溶性总糖含量呈显著正相关（r=0.87*），后期都为枳壳砧的显著高于红黎檬砧的。此外，随着果实的成熟两种砧木砂糖橘果皮中ABA含量逐渐升高，且与SS2、SUC3表达呈显著正相关，后期枳壳砧的果皮ABA含量显著高于红黎檬砧的；果肉中ABA含量变化波动不大，同样是枳壳砧的ABA水平更高。在果皮中，ABA生物合成中的限速酶NCED的基因NCED1表达趋势与ABA含量变化相似，呈上升趋势，后期枳壳砧的表达量明显高于红黎檬砧的；果肉中，枳壳砧的NCED1表达在后期明显上调，其表达量也显著高于红黎檬砧的。【结论】不同砧木对砂糖橘果实糖积累产生显著的影响。柑橘砧木主要通过影响砂糖橘果实蔗糖代谢酶的活性及其相关基因表达如SS2和CWINV1等来调节糖的代谢从而调控果实糖的积累；不同砧木也影响砂糖橘果实中内源激素ABA水平及果实糖的转运，从而影响果实糖积累。%[Objective] The effects of different rootstocks on sugar accumulation, hormone role, sucrose-related enzyme activities and gene expression of ‘Shatangju’ tangerine fruits were studied. The aim is to make research on the physiological and molecular mechanism of citrus rootstock effects on fruit sugar accumulation, and to establish a theoretical basis for the use of rootstocks in citrus production.[Method] ‘Shatangju’ tangerine, grafted on Trifoliate orange and Canton lemon rootstocks, were used in this study. The sugar content and sucrose metabolism enzyme activities were determined in fruits of ‘Shatangju’ tangerine. The expression levels of related genes, including sucrose metabolism enzymes and sucrose transport proteins, were obtained from the fruits. Meanwhile, abscisic acid (ABA) levels and expression patterns of NCED1 gene were also measured in the fruits.[Result] Results showed that total soluble sugar and sucrose content were significantly higher in both the peel and pulp of fruits on Trifoliate orange rootstocks than those on Canton lemon rootstocks at maturation stage. In the meantime, there were higher activities of sucrose synthase (SS) in the fruits on Trifoliate orange rootstocks. qRT-PCR analysis showed that the expression levels ofSS2gene were higher in the fruits on Trifoliate orange rootstocks than those on Canton lemon rootstocks. On the contrary,CWINV1 expression levels were higher in the fruits of ‘Shatangju’/Canton lemon, and was negatively related to sucrose content (r=-0.648*). Furthermore, SUC3 expression increased along with maturity and showed higher levels in the fruits of ‘Shatangju’/Trifoliate orange. There was a significantly positive correlation between SUC3 expression and total soluble sugar content (r=0.87*). In addition, the ABA concentration gradually increased in the peel during fruit ripening, and the ABA concentration was significantly and positively correlated withSS2 andSUC3 expression and significantly greater in ‘Shatangju’/Trifoliate orange after December 5. In the pulp, the ABA concentration time series followed a flattened curve, and the ABA concentration of the pulp from the ‘Shatangju’/Trifoliate orange was also greater. In the peel,NCED1 expression gradually increased with fruit ripening, and showed higher levels in ‘Shatangju’/Trifoliate orange.NCED1gene was up-regulated and exhibited significant higher levels in the pulp of ‘Shatangju’/Trifoliate orange at later stage.[Conclusion] In short, the choice of rootstock had a significant effect on sugar accumulation of ‘Shatangju’ tangerine fruits, mainly through changing the activities and gene expression patterns of sucrose metabolism enzymes, sucrose transport and ABA levels in the fruits.