百香果属于西番莲科(Passifcoracease)西番莲属(Passiflora L.),全球大约有500种百香果[1]。其中,黄色百香果(Passiflora edulis Sims)和紫色百香果(Passiflora edulis Sims f. edulis)经济价值最高[2]。百香果果实香气独特且浓郁,富含多种营养成分,深受消费者喜爱[3]。百香果是热带和亚热带特色水果,因适应性广、生长周期短和经济效益好,在我国广西、广东、福建、海南、台湾等地区的种植面积不断扩大。目前国内种植面积超过4.4万ha,年产量近60万t[4]。

果实品质可分为外观品质和内在品质。外观品质,如色泽、形状和大小等对果实的商品价值具有重要影响。百香果采后迅速成熟衰老,贮藏期间果皮的皱缩、凹陷主要由果皮失水和果皮细胞壁降解引起,严重影响果实的外观品质和商品价值。细胞壁降解与果胶代谢密切相关,果实成熟期间细胞壁原果胶逐渐降解,细胞壁结构的完整性被破坏。果胶甲酯酶(PME)、多聚半乳糖醛酸酶(PG)和β-半乳糖苷酶(β-Gal)等是主要的细胞壁降解酶,其活性和编码基因的表达受乙烯调控[5-6]。

百香果果实成熟期间乙烯合成增加,呼吸作用增强[7] 。与乙烯合成相关的1-氨基环丙烷-1-羧酸(ACC)合成酶和1-氨基环丙烷-1-羧酸氧化酶(ACO)活性增加。降低百香果乙烯合成能够延缓果实成熟,比如使用2,5-降冰片二烯(NBD)[8]、1-MCP和气调处理[9]。1-MCP具有抑制果实乙烯合成,延缓果实采后衰老的作用,被广泛用于水果采后贮藏保鲜[10]。1-MCP对百香果采后贮藏品质的影响已有报道。帅良等[11]和吉宁等[12]研究了1-MCP处理对百香果品质的影响,发现1-MCP能够抑制果实呼吸,保持果实色泽,维持百香果总可溶性固形物、维生素C 、总酸含量,降低腐烂率。孟祥春等[13]研究发现,1-MCP处理能够有效延缓百香果色泽变化,并显著降低风味组分和含量。已有的报道主要关注1-MCP对百香果品质的影响,而对其保鲜机理研究较少。因此,本研究以黄金百香果为研究对象,分析1-MCP处理对其采后贮藏期间品质、乙烯和呼吸速率的影响,并进一步分析果皮中果胶含量、细胞壁降解酶活性及成熟软化相关基因的表达,旨在探索1-MCP维持百香果采后品质的生化与分子机制。

1 材料和方法

1.1 材料与试剂

黄金百香果采自广州市增城区商业种植果园。挑选大小均匀,果形端正,无机械损伤的八成熟果实。包装材料是自主研发的双层保鲜袋(专利号:2029642)。

PrimeScriptTM RT reagent Kit试剂、SYBR® Premix Ex TaqTM Ⅱ,宝生物工程(大连)有限公司;1-甲基环丙烯、羧甲基纤维素钠、3,5-二硝基水杨酸、十六烷基三甲基溴化铵(CTAB)和多聚半乳糖醛酸,上海源叶生物科技有限公司;实验所用试剂均为国产分析纯。

1.2 仪器与设备

CR-400型色差仪,日本Konica Minolta公司;GC-2010 Plus型气相色谱仪,日本岛津公司;BioTek Synergy LX型酶标仪,美国Agilent公司;CFX Connect型定量PCR仪,美国BIO-RAD公司;Telaire-7001型二氧化碳检测仪,美国Telaire公司;PAL-BX/ACID F5型糖酸度计,日本ATAGO公司。

1.3 实验方法

1.3.1 样品处理

百香果采摘当天进行1-MCP处理。前期预实验结果显示,1.2 μL/L的1-MCP处理能有效抑制百香果采后成熟。将果实平均分成2组,实验组于20 ℃用1.2 μL/L的1-MCP密闭处理18 h,对照(CK)组空气密封。处理后,每40个果实放置在1个双层保鲜袋内,防止失水。置于(20±1)℃条件下贮藏12 d,分别于贮藏的第0、3、6、9、12天取样测定各项理化指标,每次测定取12个果实,重复3次。将果肉和果皮组织分开,果肉用于测定总可溶性固形物和可滴定酸含量,果皮液氮速冻后置于-80 ℃用于测定果胶、细胞壁降解酶活性等。

1.3.2 乙烯释放速率和呼吸速率测定

乙烯释放速率测定:取12个百香果果实置于体积为9.8 L的干燥器中,密封保持1 h。用注射器抽取容器内气体,将1 mL抽取的气体注入气相色谱仪,重复检测3次。色谱条件:RB-624毛细管柱,载气为氮气(99.99%),柱温50 ℃,进样口温度110 ℃,检测温度150 ℃。根据标准乙烯气体的保留时间和标准曲线计算乙烯释放速率。

呼吸速率测定:使用二氧化碳检测仪测定果实呼吸速率。测定仪和百香果同时密封在干燥器内,每15 min读取一次数据,连续记录3次,2次计数之间的差值用于计算果实的呼吸速率。

1.3.3 果实色泽分析

选取百香果果实赤道面3个点并使用色差仪测定其L、a*、b*。

1.3.4 总可溶性固形物和可滴定酸含量测定

采用糖酸度计测定总可溶性固形物和可滴定酸含量。取百香果果汁用于测定总可溶性固形物含量(total soluble solid,TSS),单位为%。取一定量的果汁,用蒸馏水稀释50倍,稀释后的果汁用于测定可滴定酸含量(titratable acid,TA),单位为%。

1.3.5 果胶含量测定

参照Vicente等[14]的方法,分步提取果皮水溶性果胶(water soluble pectin,WSP)和酸溶性果胶(HCl soluble pectins,HSP)。使用间羟基联苯比色法测定果胶含量,测定波长为524 nm。以半乳糖醛酸为标准品,结果以1 kg鲜重果皮中所含的半乳糖醛酸质量计(g/kg)。

1.3.6 细胞壁降解酶活性测定

参照曹建康等[15]的方法测定果皮纤维素酶(cellulase,Cel)和多聚半乳糖醛酸酶(polygalacturonase,PG)活性,参照Hagermana和Austin[16]的方法测定果胶甲酯酶(pectin methylesterase,PME)活性。

1.3.7 基因相对表达量测定

取贮藏第0、3、6、9、12天的百香果果皮样品检测基因相对表达量。利用CTAB方法提取RNA,检测提取的RNA含量和完整性。检测合格后反转录合成cDNA。采用试剂盒SYBR® Premix Ex TaqTM Ⅱ和PCR仪进行定量分析。定量反应体系设定参照戚英伟等[17]的方法。引物序列见表1。

1.4 数据处理

数值表示为平均值±标准偏差。利用SPSS 18.0软件对数据进行Student’s t-test分析,P<0.05为差异显著。使用 SigmaPlot 12.5软件绘图。

2 结果与分析

2.1 1-MCP处理对百香果果皮黄化的影响

1-MCP处理后百香果果皮色泽的变化见图1。百香果采后贮藏期间a*逐渐升高,贮藏第9天起,1-MCP组a*显著低于对照组。整个贮藏期,1-MCP组果皮b*均高于对照组,且差异不显著。L先升高后逐渐降低,贮藏第12天,1-MCP组L显著高于对照组。整体而言,贮藏12 d后,1-MCP组果皮更为鲜亮,能够更好地维持果皮色泽。

2.2 1-MCP处理对百香果TSS和TA含量的影响

1-MCP处理对百香果TSS和TA含量变化的影响见图2。由图2可知,百香果采后贮藏期间总可溶性固形物含量先升高后逐渐降低,可滴定酸含量随着贮藏时间的延长逐渐降低。在整个贮藏期间,1-MCP组总可溶性固形物和可滴定酸含量与对照组相比均无显著差异。贮藏结束时,1-MCP组总可溶性固形物和可滴定酸含量略高于对照组,但差异不显著。

2.3 1-MCP处理对百香果乙烯释放和呼吸速率的影响

百香果成熟过程中伴随着乙烯释放速率和呼吸速率的增加,1-MCP处理后百香果乙烯释放和呼吸速率变化见图3。由图3可知,采后贮藏期间对照组乙烯释放速率和呼吸速率均基本呈现先增加后降低的变化趋势,并且观察到明显的乙烯释放速率高峰和呼吸速率高峰。与对照组相比,1-MCP组乙烯释放速率被显著抑制,并且乙烯释放速率峰值[(4.6±0.6)mg·kg-1·h-1]显著低于对照组[(5.6±0.2)mg·kg-1·h-1]。1-MCP处理显著降低了百香果的呼吸速率,贮藏期间1-MCP组百香果没有观察到明显的呼吸速率高峰。贮藏结束时,2组的乙烯释放速率和呼吸速率均无显著性差异。

2.4 1-MCP处理对百香果果皮果胶分解的影响

果胶是细胞壁重要组成部分,对维持果皮质地具有重要意义。随着果实的成熟,原果胶转化为可溶性果胶,果皮组织松弛,对果肉的保护效果降低。1-MCP处理后百香果果皮果胶含量变化见图4。由图4可知,随着贮藏时间的延长,对照组和1-MCP组水溶性果胶含量均呈现先增加后降低的变化趋势,而酸溶性果胶含量逐渐降低。与对照组相比,1-MCP处理降低了2种果胶含量的变化幅度。贮藏结束时,1-MCP组的水溶性和酸溶性果胶含量分别显著低于和高于对照组,表明处理组细胞壁降解程度低于对照组。

2.5 1-MCP处理对百香果细胞壁降解酶活性的影响

1-MCP处理后百香果果皮细胞壁降解酶活性变化见图5。由图5可知,百香果贮藏期间对照组的PG、PME和Cel活性均呈现先升高后下降的趋势。与对照组PG和Cel贮藏前期酶活性迅速增加不同,1-MCP组PG和Cel活性在贮藏期间逐渐降低。对照组PG活性在整个贮藏期间始终显著高于1-MCP组,Cel活性在第3天和第9天时显著高于1-MCP组(P<0.05)。1-MCP组PME活性变化趋势与对照组一致,只在贮藏第6天时具有显著差异。

2.6 1-MCP处理对百香果乙烯合成酶和细胞壁降解酶基因表达的影响

百香果乙烯生物合成基因(ACS1、ACO1)和细胞壁降解酶基因(PME1、XTH16/28/30、PG1、GAL1)定量结果见图6。由图6可知,采后贮藏期间1-MCP组和对照组百香果ACS1和ACO1的表达水平基本上先增加后降低。对照组ACS1和ACO1表达量高于1-MCP组,且分别在第6、9天和第3、6天时具有显著性差异(P<0.05)。对照组ACS1和ACO1分别在贮藏第9天和贮藏第6天达到峰值,随后下降。与对照组相比,1-MCP组ACS1和ACO1表达水平在贮藏前期(0～6 d)缓慢增加,ACO1表达量在贮藏第9天时达到峰值,且低于对照组;没有观察到ACS1的表达峰值。百香果贮藏结束时对照组和1-MCP组ACS1和ACO1的表达量没有显著性差异。

细胞壁降解酶编码基因的表达趋势为先升高后降低。对照组PME1表达量在贮藏第6天迅速升高,且显著高于1-MCP组;之后降低,贮藏结束时显著高于处理组。贮藏前期(0～6 d),对照组XTH16/28/30的表达量均显著高于1-MCP组。贮藏结束时,XTH16和XTH30表达量分别显著低于和高于1-MCP组,XTH28表达量无显著差异。对照组PG1表达量在第3天,β-半乳糖苷酶编码基因GAL1表达量在第3和第9天显著高于1-MCP处理组,其他时间2组的PG1和GAL1表达量均无显著差异。

3 讨 论

1-MCP能够延缓呼吸跃变型果实成熟,在园艺产品采后贮藏保鲜方面应用广泛。百香果采后迅速成熟衰老,表现为果皮色泽暗淡、失水皱缩、果皮塌陷,直至腐烂,严重影响百香果商品价值。1-MCP处理能够有效抑制百香果果实呼吸作用,延缓果实成熟,保持果实色泽,同时较好地维持果实TSS、维生素C、总酸、总酚和总糖含量,并降低贮藏期间的腐烂率[11-13]。本研究同样发现,1-MCP处理能够抑制百香果乙烯合成,降低果实呼吸作用,较好地保持果实形态和色泽,抑制果胶分解,降低细胞壁降解酶活性及成熟相关基因的表达。

乙烯能控制呼吸跃变型果实的成熟。呼吸跃变型果实成熟过程中伴随着乙烯释放量增加和呼吸作用增强[18-19]。本研究发现,百香果采后贮藏期间,果实乙烯释放速率增加,呼吸作用增强,这与Shiomi等[7]的研究结果一致。1-MCP是乙烯竞争性抑制剂,能够阻断乙烯与其受体的结合[20-21]。本研究发现,1-MCP组百香果乙烯释放速率峰值和呼吸作用强度峰值均显著低于对照组(图3)。这表明1-MCP处理能够抑制百香果采后贮藏期间果实乙烯生成速率和呼吸作用速率,研究结果与番茄[22]、苹果[18]、香蕉[23]和梨[24]等跃变型果实的研究结果一致。

植物体内ACS和ACO是乙烯生物合成的关键酶。呼吸跃变型果实成熟期间,编码基因中关键成员的表达量与乙烯合成密切相关[25-26]。外源乙烯处理可增加乙烯合成相关基因的转录水平,促进果实内源乙烯的合成,而使用1-MCP则具有相反的作用[27-29]。百香果ACS1和ACO1是果实乙烯生物合成的关键基因并且表达量受乙烯调控[8]。本研究发现,1-MCP处理显著抑制了百香果ACO1和ACS1的表达(图6),并且降低了乙烯的合成(图3)。处理组果实乙烯生成速率在贮藏第6天达到峰值[(4.6±0.6) mg·kg-1·h-1],较对照组峰值(贮藏第9天)低19%[(5.6±0.2) mg·kg-1·h-1]。这表明1-MCP通过抑制百香果果实乙烯生物合成基因的表达,降低了百香果果实乙烯生物合成。

果实细胞壁降解引起细胞壁结构改变,导致果实软化[30]。Giongo等[31]认为果实软化过程中硬度的降低主要与总果胶含量减少、初生壁和中胶层降解有关。本研究发现,随着贮藏时间的延长,2组百香果水溶性果胶含量均先增加后降低,而酸溶性果胶含量均逐渐降低,表明随着贮藏时间的延长,果皮细胞壁逐渐降解。细胞壁降解酶在细胞壁降解方面起重要作用。其中,PME催化果胶去甲基化、破坏酸性多糖链的水平钙链接并导致细胞分离[32]。PG能够降解多聚半乳糖醛酸,与PME共同作用将果胶分解成水溶性果胶和果胶酸[33]。Cel在纤维素和木葡聚糖的β-1,4-葡聚糖骨架降解方面发挥作用[34]。乙烯正向调控跃变型果实细胞壁降解酶编码基因的表达及酶活性,而1-MCP对其具有抑制作用[5-6,30]。本研究发现,1-MCP处理显著抑制了贮藏期间百香果PG活性,处理组的Cel活性在贮藏第3天和第9天显著低于对照组。基因定量结果显示,对照组PME1表达量在贮藏第6天迅速升高,且显著高于1-MCP组。贮藏前期(0～6 d),对照组XTH16/28/30的表达量均显著高于1-MCP组,PG1表达量在第3天,GAL1表达量在第3天和第9天显著高于1-MCP组。这表明1-MCP处理抑制了细胞壁降解酶编码基因的表达量,降低了细胞壁降解酶的活性,从而降低百香果细胞壁降解反应。与之对应,1-MCP组酸溶性果胶含量高于对照组,而水溶性果胶含量低于对照组(图4)。之前的研究同样发现,1-MCP处理显著抑制跃变型果实,如梨[35]果实软化相关酶(PME、Cel和PG等)活性和基因的表达,延缓果实贮藏期间细胞壁组分的降解和果实硬度的下降。

4 结 论

百香果采后室温贮藏期间,果实乙烯释放速率增加,呼吸作用增强。果肉总可溶性固形物和可滴定酸含量逐渐降低,果皮褪绿转黄。1-MCP处理抑制了果皮转黄,较好地维持了果皮色泽,对果肉总可溶性固形物和可滴定酸含量具有一定的维持作用。进一步研究发现,1-MCP通过抑制百香果乙烯合成基因和细胞壁降解酶基因的表达,降低了乙烯合成和细胞壁降解酶活性,从而延缓了百香果采后成熟进程。

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Effects of 1-MCP on Ethylene Synthesis, Cell Wall Degradation and Related Genes Expression in Passion Fruit

QI Yingwei1,2, JIANG Yonghua3,*, CHEN Yulong1, WANG Ling1, CHEN Feiping1, LUO Zheng1, CHEN Minhui1, YE Mingqiang1, DAI Fanwei1,*

(1.Sericultural &Agri-Food Research Institute/Key Laboratory of Functional Foods, Ministry of Agriculture and Rural Affairs/Guangdong Key Laboratory of Agricultural Products Processing, Guangdong Academy of Agricultural Sciences, Guangzhou 510640, China; 2. Heyuan Branch, Guangdong Laboratory for Lingnan Modern Agriculture, Heyuan 517500, China 3. Institute of Fruit Tree Research/Key Laboratory of South Subtropical Fruit Biology and Genetic Resource Utilization, Ministry of Agriculture and Rural Affairs/Guangdong Provincial Key Laboratory of Science and Technology Research on Fruit Tree, Guangzhou 510640, China)

Abstract：In order to illustrate the effect and underlying mechanism of 1-methylcyclopropene (1-MCP) treatment on room temperature storage of passion fruit, golden passion fruit was used as experimental material. Commercial mature passion fruit was treated by 1.2 μL/L 1-MCP and stored at (20±1)℃ for 12 d, and the untreated fruit was used as control. During storage, ethylene release rate, respiration rate, total soluble solid content, pectin content, cell wall degrading enzymes activities were measured every 3 d. The expression levels of ethylene biosynthesis genes (ACS1 and ACO1) and cell wall-degrading enzyme encoding genes (PME1, XTH16/28/30, PG1 and GAL1) in passion fruit were analyzed. Compared with control, 1-MCP treatment decreased ethylene release rate and respiration rate of passion fruit, and inhibited the expression of key ethylene biosynthesis genes ACS1 and ACO1. The contents of acid-soluble pectin and water-soluble pectin in 1-MCP treatment group were significantly higher and lower than that in control, respectively. It was also found that 1-MCP treatment reduced polygalacturonase and cellulase activities, and inhibited the expression of PME1, XTH/16/28/30 and GAL1. Moreover, a* and L in 1-MCP treatment group were significantly lower and higher respectively than that in control at the end of storage. There was no significant difference on total soluble solid and titrable acid contents between 1-MCP treatment and the control during the whole storage time. In conclusion, 1-MCP inhibited endogenous ethylene synthesis in passion fruit by decreasing the expression of ethylene biosynthesis genes ACS1 and ACO1, and inhibited cell wall degradation by decreasing cell wall-degrading enzymes activities and reducing expression of encoding genes including PME1, XTH/16/28/30 and GAL1, thereby delaying the postharvest ripening process of passion fruit and demonstrating a good preservation effect on passion fruit.

Keywords：passion fruit; ethylene; 1-methylcyclopropene; cell wall degradation; gene expression

中图分类号：TS255.36

文献标志码：A

doi：10.12301/spxb202400138

文章编号：2095-6002(2025)01-0096-10

引用格式：戚英伟,姜永华,陈于陇,等.1-MCP对百香果乙烯合成和细胞壁降解及相关基因表达的影响[J]. 食品科学技术学报,2025,43(1):96-105.

QI Yingwei, JIANG Yonghua, CHEN Yulong, et al. Effects of 1-MCP on ethylene synthesis, cell wall degradation and related genes expression in passion fruit[J]. Journal of Food Science and Technology, 2025,43(1):96-105.

收稿日期：2024-03-06

基金项目：岭南现代农业科学与技术广东省实验室河源分中心自主科研项目(DT20220025);广州市科技计划项目(2023AO4J0825);广东省农业科学院创新基金项目(202211);广东省农业科学院青年导师制项目(R2020QD-039)。

Foundation：Heyuan Branch of Guangdong Laboratory for Lingnan Modern Agriculture Project (DT20220025); Science and Technology Projects in Guangzhou (2023AO4J0825); Innovation Fund Project of Guangdong Academy of Agricultural Sciences (202211); Youth Mentor Project of Guangdong Academy of Agricultural Sciences (R2020QD-039).

第一作者：戚英伟,男,助理研究员,博士,主要从事生鲜农产品贮藏保鲜方面的研究。

*通信作者：姜永华,女,副研究员,博士,主要从事南方特色水果采后保鲜方面的研究;戴凡炜,女,研究员,博士,主要从事农产品物流与保鲜方面的研究。

(责任编辑：张逸群)