Correlation with Cell Wall Metabolizing-related Enzymes and Microstructure Observation in Texture Differences of two Kinds of High-Quality Pear Fruit
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摘要:
目的 通过对果实质地差异明显的2个梨品种进行质地差异相关研究,旨在发现导致梨品种果实质地差异的关键因素,为优良梨品种的选育提供理论依据。 方法 以玉露香梨和大果水晶梨为试材,观察发育过程中果肉细胞超显微结构,测定果实的硬度、脆度值、细胞壁代谢相关酶的活性和相关基因的相对表达量,并进行相关性分析。 结果 ①果实生长发育过程中玉露香梨和大果水晶梨果实硬度逐渐下降,且花后60 d 2个梨品种脆度值逐渐下降,玉露香梨果实硬度和脆度值显著低于大果水晶梨。②在400×放大显微倍数下,幼果期玉露香梨果肉细胞比大果水晶梨的大;果实膨大期和成熟期,2个梨品种果肉细胞均明显增大,玉露香梨果肉细胞小于大果水晶梨;玉露香梨细胞断裂边缘整齐平滑,形成脆性断口,大果水晶梨断裂边缘粗糙而不整齐。③果实发育过程中玉露香梨果肉果胶甲酯酶(Pectin methylesterase,PME)活性极显著低于大果水晶梨,而多聚半乳糖醛酸酶(Polygalacturonase,PG)活性和β-半乳糖苷酶(β- Galactosidase,β-Gal)活性极显著高于大果水晶梨。④果实发育过程中玉露香梨果肉PME基因、PG基因和β-Gal基因相对表达量极显著低于大果水晶梨的表达量。相关性分析表明,玉露香梨和大果水晶梨的硬度与β-Gal 基因相对表达量呈显著正相关,脆度值与PG 基因相对表达量呈显著正相关。 结论 随着果实生长发育,玉露香梨和大果水晶梨果实质地的差异不仅表现在果肉细胞超显微结构上,还与细胞壁代谢相关酶密切相关,PG基因和β-Gal 基因可能在玉露香梨和大果水晶梨质地变化中发挥关键作用。 Abstract:Objective Factors contributing to the distinctively different texture of the fruits of two pear cultivars were investigated. Method Cellular microstructures of the pulp of Yuluxiangli and Daguoshuijingli pears were observed under an electron microscope SU810 . Textural firmness and brittleness, as well as contents of cell wall-modifying enzymes and relative expressions of the associated genes, of the fruits during develop stages were measured to correlate with the microstructure observations. Result ①The firmness of the pears of both varieties gradually declined during the fruit development. The force required to break into the fruit decreased 60d after flowering as the fruits were ripening. In comparison, Yuluxiangli pears were significantly softer and less brittle than Daguoshuijingli. ②At 400× magnification, the cells of Yuluxiangli pear pulp appeared larger than those of Daguoshuijingli at young stage. As the fruits expanded and matured, the cells of both varieties enlarged significantly but those of Yuluxiangli became smaller than those of Daguoshuijingli. And upon cutting, the edge of fractured Yuluxiangli pears were clean and smooth, while that of Daguoshuijingli rough and irregular. ③ In the matured fruits, the pectin methylesterase (PME) activity in Yuluxiangli pears were extremely significantly lower than that in Daguoshuijingli, whereas the polygalacturonase (PG) and β-galactosidase (β-Gal) activities extremely significantly higher. ④ The relative expressions of PME, PG, and β-Gal in Yuluxiangli were extremely significantly lower than those in Daguoshuijingli during the fruit development. And that of β-Gal was significantly positively related to the textural firmness, but that of PG to the brittleness, of the fruits for both pear varieties. Conclusion The unique texture of Yuluxiangli and Daguoshuijingli pears could not only be differentiated by their pulp cell ultrastructural differences but also closely related to the cell wall-modifying enzymes, such as, PG and β-Gal, in the fruits. Hence, the genes associated with those enzymes likely played a critical role in the texture of the pears. -
Key words:
- Pears /
- distinct texture /
- ultrastructure of pulp cell /
- cell wall-modifying enzymes
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图 2 不同梨品种果实发育过程中果肉细胞超显微结构
a~c:玉露香梨果实幼果期、膨大期、成熟期;A~C:大果水晶梨果实幼果期、膨大期、成熟期。
Figure 2. Ultrastructure of pear pulp cells during fruit development
a: Yuluxiangli pear at young stage; b: Yuluxiangli pear at fruit expanding stage; c: Matured Yuluxiangli pear; A: Daguoshuijingli pear at young stage; B: Daguoshuijingli pear at fruit expanding stage; C: Matured Daguoshuijingli pear.
表 1 qPCR引物
Table 1. Primers for qPCR
基因
Gene引物序列
Primer sequence片段大小
Amplified fragment length/bpGenBank 登录号
GenBank Accession No.果胶甲酯酶PME F:5′-CAAAGCAGGAAGGTACGAAGAG-3′ 121 AB067681.1 R:5′-TTTCTGCGCGACGTTTTTC-3′ β-半乳糖苷酶β-Gal F:5′-GTGTATGGGTCGTTGGAGAATC-3′ 102 AJ811694.1 R:5′-CAGACCAACGGAAATGCTAAG-3′ 多聚半乳糖醛酸酶PG F:5′-GCAATAACTTGGTGGTGAAGAATC-3′ 132 AJ504855.2 R:5′-CGTCCGTATTAGGGCTATCCTC-3′ Actin F:5'-TGCTGAGCGGGAAATTGTG-3' 145 AF386514.1 R:5′-TCCGATAGTGATTACCTGTCCATC-3′ 表 2 果实质地与细胞壁代谢相关酶活性及相关基因表达量的相关性分析
Table 2. Correlation between texture, cell wall metabolism-related enzyme activity, and related genes expressions of pears
品种
Variety指标
IndicatorPME活性
Activity of PMEPG活性
Activity of PGβ-Gal活性
Activity of β-GalPME 相对表达量
PME relative expressionPG 相对表达量
PG relative expressionβ-Gal 相对表达量
β-Gal relative expression玉露香梨
Yuluxiangli硬度
Firmness0.974 0.997* 1.000** 0.963 0.945 1.000* 脆度值
Fracturability0.989 0.954 0.924 0.994 0.999* 0.936 大果水晶梨
Daguoshuijingli硬度
Firmness1.000* 0.992 0.985 1.000* 0.984 0.998* 脆度值
Fracturability0.977 0.994 0.998* 0.970 0.998* 0.984 ** 表示极显著相关( P <0.01),* 表示显著相关( P <0.01)。
** indicates extremely significant correlation( P <0.01); * indicates significant correlation (P <0.01). -
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