宽皮柑橘果实的剥皮性及与细胞壁多糖的关系

Ease of Peeling and Its Relationship with Cell Wall Polysaccharides in Mandarin Fruit

以‘向山’(Citrus reticulata Blanco‘Mukaiyama’)、‘克里曼丁’(C. clementina hort.ex. Tanaka)、‘弗莱蒙特’(C. reticulata Blanco‘Fremont’)和‘药香柑’(C. reticulata Blanco‘Yaoxianggan’)4种宽皮柑橘为试材,比较分析了果实成熟过程不同时期的剥皮性、果皮形态、细胞壁多糖含量、细胞壁多糖降解相关酶活性及部分基因表达的变化。在果实成熟过程中,反映剥皮性的两个力学指标(果皮粘力和硬度)均显著下降。不同材料的剥皮性有所差异,‘药香柑’与‘弗莱蒙特’的果皮粘力较高,‘克里曼丁’和‘向山’较低;‘药香柑’的果皮硬度最高,‘弗莱蒙特’次之,‘克里曼丁’和‘向山’最低。相关性分析表明果皮粘力和硬度呈显著正相关,且易剥皮性状与低水平的细胞壁多糖物质和高水平的细胞壁多糖降解相关酶活性密切相关。在果实成熟过程中,4种柑橘果皮中的多种细胞壁多糖组分的含量均有不同程度的下降,参与细胞壁降解的酶活性及部分编码基因表达水平随之上升,另有部分编码木聚糖酶抑制蛋白和果胶甲酯酶抑制蛋白的基因下调表达。易剥皮的‘向山’和‘克里曼丁’果皮中的总细胞壁干物质和部分细胞壁多糖组分(半纤维素、纤维素、原果胶)的含量低于难剥皮的‘药香柑’和‘弗莱蒙特’,这可能与木聚糖酶、纤维素酶和多种果胶降解相关酶的活性水平较高有关。

To clarify the relationship between the ease of peeling of mandarins and cell wall polysaccharides,which are thought to support the plant cell integration,adherence and mechanical strength,the ease of peeling,peel morphology,cell wall polysaccharide contents,the activities of the enzymes related to cell wall polysaccharide degradation and the expression level of some related genes were analyzed in four mandarin varieties,Citrus reticulata Blanco ’Mukaiyama’,C. clementina hort. ex.Tanaka,C. reticulata Blanco ’Fremont’and C. reticulata Blanco ’Yaoxianggan’. During the fruit ripening,peel adherence and firmness,which reflect the ease of peeling,remarkably decreased,suggesting that the peeling is easier as the fruit mature. In different varieties,the ease of peeling also showed great diversity. Fremont and Yaoxianggan had higher peel adherence than Mukaiyama and Clementine,and Yaoxianggan had the highest peel firmness in the four varieties,whereas Mukaiyama and Clementine had the similarly lowest peel firmness,indicating that Fremont and Yaoxianggan were hard peeling and Mukaiyama and Clementine were easy peeling. The correlation analysis indicated the significant positive correlation between the peel adherence and firmness,and that the ease of peeling is relevant to the low level of cell wall polysaccharides and high activities of their degradation-related enzymes. The contents of cell wall polysaccharides in all varieties dramatically dropped during the fruit maturation, and coincidently,the activities of some enzymes related to cell wall polysaccharide degradation and the expression level of the encoded genes also ascended. At the same time the expression of some genes encoding xylanase inhibitors and pectin methylesterase inhibitors was decreased. In these four varieties,the peels in the easy-peeling Mukaiyama and Clementine had lower content of total cell wall biomass as well as some polysaccharide fractions including hemicellulose,cellulose and protopectin,which were relevant to the higher activities of xylanase, cellulose and pectin degradation-related enzymes.Nevertheless,the pivot gene controlling the distinct ease of peeling in different varieties remains obscure.