枇杷冷藏过程中果肉木质化与细胞壁物质变化的关系

“大红袍”和“解放钟”枇杷果实在 1℃下贮藏时 ,细胞壁物质代谢异常 ,果肉硬度持续升高而出汁率逐渐降低 ,果胶酯酶 (PE)和多聚半乳糖醛酸酶 (PG)活性和水溶性果胶含量下降 ,原果胶含量、苯丙氨酸解氨酶(PAL)活性及木质素和纤维素含量不断增加。约经 3周贮藏后 ,果实出现果皮难剥、果肉质地变硬、粗糙少汁的异常劣变现象。在 12℃下贮藏的枇杷果实 ,细胞壁物质代谢正常 ,果肉硬度增加少 ,PE和PG活性及水溶性果胶含量较高 ,无原果胶增加现象 ,PAL活性呈下降趋势 ,木质素和纤维素含量变化不大 ,果实不出现木质化败坏。这些结果表明冷藏枇杷的木质化败坏可能是一种低温失调现象     

枇杷冷藏过程中果肉木质化与细胞壁物质变化的关系

“大红袍”和“解放钟”枇杷果实在１℃下贮藏时,细胞壁物质代谢异常,果肉硬度升高而出汁率逐渐降低,果胶酯酶（ＰＥ）和多聚半乳糖醛酸酶（ＰＧ）活笥和水溶性果胶含量下降,原果胶含量、苯丙氨酸解氨酶（ＰＡＬ）活性及木质素和纤维含量不断增加。约经３周贮藏后,果实出现果皮难剥、果肉质地变硬、粗糙少汁的异常劣变现象。在１２℃下贮藏的枇杷果实,细胞壁物质代谢正常,果肉硬度增加少,ＰＥ和ＰＧ活性及水溶性果胶含量较遍     

桃果实絮败与果胶质变化和细胞壁结构的关系

“白凤”桃果实在０℃下贮藏２０ｄ以后出现肉质发棉和干化的絮败现象。冷藏第１０天在１８℃下加温３８ｈ能有效减缓絮败的发生。连续冷藏１０ｄ以后,原果胶含量开始增多,水溶性果胶含量变化不大。中途加温的果实原果胶含量变化不多,但水溶性果胶却不断增加。絮败果的果胶质粘度明显高于正常果。果肉出汁率是测定果实絮败程度的理想指标,絮败果肉细胞壁的明显特征是：伴随胞间层的分解和胞间隙的扩大,出现大量凝胶状物质的沉积     

桃果实絮败与果胶质变化和细胞壁结构的关系

“白凤”桃果实在０ ℃下贮藏２０ ｄ 以后出现肉质发绵和干化的絮败现象。冷藏第１０ 天在１８ ℃下加温３８ ｈ 能有效减缓絮败的发生。连续冷藏１０ ｄ 以后,原果胶含量开始增多, 水溶性果胶含量变化不大。中途加温的果实原果胶含量变化不多,但水溶性果胶却不断增加。絮败果的果胶质粘度明显高于正常果。果肉出汁率是测定果实絮败程度的理想指标。絮败果肉细胞壁的明显特征是： 伴随胞间层的分解和胞间隙的扩大,出现大量凝胶状物质的沉积,初生壁结构变化不明显, 也没有细胞壁次生加厚的迹象。     

采后钙处理对梨果实钙的形态和果胶及相关代谢酶类影响的研究

研究了黄花梨经浸钙处理后,果实钙形态转变及果胶含量、多聚半乳糖醛酸酶（PG）和果胶甲酯酶（PME）活力的变化,以及果实硬度的变化。结果表明：浸钙处理的果实总钙含量显著提高,其硬度明显高于对照,且有利于细胞膜透性的保持;梨果实中的NaCl溶性钙最多,其次是水溶性钙,醋酸溶性钙和HCl溶性钙含量较少。在果实贮藏21d时,水溶性钙含量有一个上升的过程,而NaCl溶性钙则有一个下降的过程。浸钙处理后,除醋酸溶性钙外,果实中的水、NaCl和HCl溶性钙含量均有显著的提高。浸钙处理明显抑制了果胶的降解进程与PG的活力,但对PME抑制作用不明显。浸钙处理能提高果实硬度可能与浸钙处理抑制了PG活力有关。     

赤霉素和萘乙酸对柿果实采后成熟软化生理指标的影响

以采后'富平尖柿'果实为试材,常温下用60 mg/L赤霉素(GA3)和20 mg/L α-萘乙酸(NAA)进行处理,考察柿果实成熟软化相关生理指标及果胶物质代谢在贮藏过程中的变化,以明确GA3和NAA处理对柿果实贮藏效果的影响.结果显示:GA3、NAA处理果实的贮藏时间分别比对照延长了4 d和10 d;GA3和NAA处理可显著延缓果实硬度的下降进程,有效降低果实呼吸强度和乙烯释放量,且呼吸高峰和乙烯高峰的出现明显迟于对照;果实多聚半乳糖醛酸酶(PG)活性的升高受到抑制,从而延缓了原果胶的降解以及水溶性果胶含量的增加,阻碍了果实的软化进程.试验表明,GA3和NAA处理可有效延缓柿果实的后熟软化,延长其贮藏期限, 并以GA3的效果尤为明显.     

冷藏方式对桃采后果胶含量和β-半乳糖苷酶活性的影响

以采后包装和不包装的'大久保'桃果实为材料,分别测定了其在8℃冷藏(A)、8℃冷藏10 d后转入0℃贮藏(B)和0℃冷藏(C)方式下的硬度、出汁率、果胶含量和β-半乳糖苷酶活性的变化.结果表明:在A、B冷藏方式下,包装较不包装处理显著抑制了果实的硬度下降、原果胶含量减少和可溶性果胶含量增加,降低了果实出汁率和β-gal活性;与冷藏期比较,货架期后冷藏方式A和B果实表现为硬度下降、原果胶含量减少、可溶性果胶含量增加,以及出汁率和β-gal活性升高.与冷藏方式A和B比较,冷藏方式C果实的硬度和原果胶含量较高,出汁率和可溶性果胶含量较低;货架期后,不包装的果实硬度和原果胶含量增加,可溶性果胶含量和β-gal活性降低,但包装处理却能减缓上述现象的发生.研究表明,桃采后用30 μm聚乙烯袋包装、于8℃冷藏10 d后转入0℃贮藏处理,能使桃果实在贮藏期保持较低的可溶性果胶含量和较高的原果胶含量和出汁率,并能使桃在货架期正常后熟软化,是贮藏桃的一种较好方式.     

限气贮藏猕猴桃果实伤害产生机制的研究

采用ＰＥ袋方法于常温一藏秦猕猴桃,贮藏期间袋内ＣＯ２浓度高于６％时果实会产生伤害贮藏前期,果实的果肉和果心硬度均很高,这与两部位淀粉酶和多聚半乳糖醛酸酶活性严重被抑制淀粉和果胶物质水解被抑制有关。贮藏中期,果肉出现水浸状,到贮藏末期,果心和照相机人均很快腐烂,这主要与Ｖｃ含量明显降低,导致膜脂过氧化加剧有关。而与ＳＯＤ活性变化关系不大。而贮藏期间,果心硬度明显高于果肉,这与果心淀粉酶和多聚半乳醛酸     

1-甲基环丙烯处理对采后杨桃果实软化和细胞壁代谢的影响

为探讨1-甲基环丙烯(1-methylcyclopropene, 1-MCP)延缓采后杨桃果实软化的作用机理,本文研究了0.6 μL/L 1-MCP处理对在(15±1)℃、相对湿度90%下贮藏的‘香蜜’甜杨桃(Averrhoa carambola Linn. cv. Xiangmi)果实软化和细胞壁代谢的影响。结果表明：与对照果实相比,1-MCP处理可保持较高的杨桃果实硬度,有效降低果胶酯酶(pectinesterase, PE)、多聚半乳糖醛酸酶(polygalacturonase, PG)、纤维素酶等细胞壁降解酶活性,延缓原果胶、纤维素、半纤维素含量的下降和水溶性果胶含量的增加。因此认为,0.6 μL/L 1-MCP处理能有效控制采后‘香蜜’甜杨桃果实的软化进程,延长果实保鲜期。     

花期减少施钙量对不同钙效率番茄果实钙形态和含量的影响

花期降低施钙量后,钙低效番茄品种L-402果实中钙含量显著降低,高效品种江蔬一号降低不显著,镁含量显著增加,钾含量有增加趋势。果实底端的钙含量高于顶端,降低施钙量后果实水溶性钙含量和比例显著提高,果胶酸钙含量和比例降低,磷酸钙含量也降低。钙低效品种L-402水溶性钙含量的增加,以及果胶酸钙和磷酸钙的降低程度,都大于高效品种江蔬一号,且降钙后果实顶端的革酸钙含量和比例增加。     

猕猴桃软化过程中阶段性专一酶活性变化的研究

猕猴桃（Ａｃｔｉｎｉｄｉａ ｄｅｌｉｃｉｏｓａ Ｃ．Ｆ．Ｌｉａｎｇ ｅｔＡ．Ｒ．Ｆｅｒｇｕｓｏｎ． ｃｖ． Ｑｉｎｍ ｅｉ）果实采后的软化过程表现为两个明显的阶段,第一阶段软化较快,此时对软化起主要作用的阶段性专一酶是淀粉酶;第二阶段软化速度变慢,此时起主要作用的阶段性专一酶是多聚半乳糖醛酸酶和纤维素酶。乙烯形成酶（ＥＦＥ）的活性高峰出现在两个软化阶段之间,它所引起的乙烯释放对软化有促进作用,因此ＥＦＥ也是与果实软化有关的阶段性专一酶。但是,果胶甲酯酶（ＰＭＥ）的活性变化与果实的软化无相关关系,过氧化物酶（ＰＯＸ）、过氧化氢酶（ＣＡＴ）和ＳＯＤ的活性高峰出现在果实完全软化以后,因此不是果实软化的阶段性专一酶     

Study on the Activities of Stage Specific Enzyme During Softening of Kiwifruit

The activities of several stage specific enzymes (SSE) and the changes of some compounds during softening of “Qinmei” kiwifruit (Actinidia deliciosa) were studied. The resuits showed that there were two phases of kiwifruit softening. Firstly the rapid softening phase was coincided with starch degradation (r= 0. 99) and the increase of amylase activity. It suggested that amylase was the key SSE for softening at this phase. In the second phase, the rate of softening was decreased, the contents of water insoluble pectin and cellulose apparently were reduced and the activities of polygalacturoase (PG) and cellulase were markedly increased, which indicated the PG and cellulase were the key SSE in the second softening phase. Besides, ethylene forming enzyme (EFE) activity and ethylene production were at their peaks between the two phases as they might play the part as triggers of the PG and cellulase activities. The experiments also showed that the activity of pectin methylesterase (PME) was not related to the softening of kiwifruit. The maximum activities of peroxidase (POX), catalase (CAT) and superoxide dismutase (SOD) were found after the softening stages. It seemed that they were not the key SSE for the softening of kiwifruit.     

1-甲基环丙烯(1-MCP)对油桃果实软化的影响

1-甲基环丙烯(1-MCP)可延缓油桃果实硬度的下降,阻止引起果实软化的细胞物质(淀粉、纤维素、果胶)的降解,抑制与果实软化相关的酶(淀粉酶、纤维素酶、多聚半乳糖醛酸酶)活性。     

猕猴桃果实采后成熟过程中糖代谢及其调节

20℃下采后猕猴桃果实中淀粉酶活性快速上升于果实软化启动阶段,随着果实进入快速软化阶段,淀粉迅速水解,葡萄糖和果糖快速积累,SPS活性增加,酸性转化酶活性下降,蔗糖积累;至果实软化后期,SPS活性降低,蔗糖含量下降.AsA和低温可抑制淀粉酶活性、己糖积累、SPS活性上升和酸性转化酶活性下降,延缓蔗糖积累,相反,乙烯则可促进淀粉酶活性,加速淀粉降解和己糖积累进而直接或间接增加SPS活性,促使蔗糖积累.采后猕猴桃果实的SPS活性变化中有己糖激活效应和蔗糖反馈抑制效应.AsA、低温和乙烯等对糖代谢的调节主要是通过对SPS活性的影响而实现的.     

Cell wall metabolism in fruit softening and quality and its manipulation in transgenic plants

Excessive softening is the main factor limiting fruit shelf life and storage. Transgenic plants modified in the expression of cell wall modifying proteins have been used to investigate the role of particular activities in fruit softening during ripening, and in the manufacture of processed fruit products. Transgenic experiments show that polygalacturonase (PG) activity is largely responsible for pectin depolymerization and solubilization, but that PG-mediated pectin depolymerization requires pectin to be de-methyl-esterified by pectin methylesterase (PME), and that the PG -subunit protein plays a role in limiting pectin solubilization. Suppression of PG activity only slightly reduces fruit softening (but extends fruit shelf life), suppression of PME activity does not affect firmness during normal ripening, and suppression of -subunit protein accumulation increases softening. All these pectin-modifying proteins affect the integrity of the middle lamella, which controls cell-to-cell adhesion and thus influences fruit texture. Diminished accumulation of either PG or PME activity considerably increases the viscosity of tomato juice or paste, which is correlated with reduced polyuronide depolymerization during processing. In contrast, suppression of -galactosidase activity early in ripening significantly reduces fruit softening, suggesting that the removal of pectic galactan side-chains is an important factor in the cell wall changes leading to ripening-related firmness loss. Suppression or overexpression of endo-(1\to4)-d-glucanase activity has no detectable effect on fruit softening or the depolymerization of matrix glycans, and neither the substrate nor the function for this enzyme has been determined. The role of xyloglucan endotransglycosylase activity in softening is also obscure, and the activity responsible for xyloglucan depolymerization during ripening, a major contributor to softening, has not yet been identified. However, ripening-related expansin protein abundance is directly correlated with fruit softening and has additional indirect effects on pectin depolymerization, showing that this protein is intimately involved in the softening process. Transgenic work has shown that the cell wall changes leading to fruit softening and textural changes are complex, and involve the coordinated and interdependent activities of a range of cell wall-modifying proteins. It is suggested that the cell wall changes caused early in ripening by the activities of some enzymes, notably -galactosidase and ripening-related expansin, may restrict or control the activities of other ripening-related enzymes necessary for the fruit softening process.     

Changes in the cell-wall polysaccharides of outer pericarp tissues of kiwifruit during development.

Changes in pectin, hemicelluloses and cellulose in the cell walls of outer pericarp tissues of kiwifruit (Actinidia deliciosa cv. Hayward) were determined during development. An extensive amylase digestion was employed to remove possible contaminating starch before and after fractionation of wall polysaccharides. An initial treatment of crude cell walls with alpha-amylase and iso-amylase or DMSO, was found to be insufficient removing the contaminating starch from wall polysaccharides. After EDTA and alkaline extraction, the pectic and hemicellulose fractions were again treated with the combination of alpha-amylase and iso-amylase. The amounts of predominant pectic sugars Gal, Rha and Ara, unaffected by the first and second amylase digestion, decreased markedly during the early fruit enlargement (8-12 weeks after anthesis, WAA), then increased during 16-20 WAA, and finally declined during fruit maturity (20-25 WAA). The molecular-mass of pectic polysaccharides decreased during fruit enlargement (8-16 WAA), and then changed little during fruit maturity. The higher molecular-mass components of hemicelluloses in HC-I and HC-II fractions detected at the early stage of fruit enlargement (8-12 WAA) were degraded at the late stage of fruit enlargement (16 WAA), but then remained stable at the much lower molecular-mass till fruit maturity. The amount of Xyl in the HC-II fraction decreased during the early fruit enlargement and fruit maturity, an observation that was consistent with xyloglucan (XG) content. The gel permeation profiles of XG showed a slight increase in higher molecular-mass components during 8-12 WAA, but thereafter there was no significant down-shift of molecular-mass until harvest time. The cellulose fraction increased steadily during fruit enlargement through maturity, but the XG contents in HC-I and HC-II fractions remained at a low level during these stages. Methylation analysis of HC-I and HC-II fractions confirmed the low level of XG in the hemicellulosic fractions. It was suggested that pectin in the outer pericarp of kiwifruit was degraded at the early stage of fruit enlargement, but XG remains constant during fruit enlargement and maturation.     

猕猴桃果实采后生理研究进展

猕猴桃（Actinidia chinensis Planch.）属于呼吸跃变型果实,采后易软化腐烂,不耐贮藏,如何延长猕猴桃果实贮藏期限已成为猕猴桃产业发展壮大亟待解决的问题。猕猴桃果实采后生理变化强烈影响果实的贮藏期限和果实品质,特别是呼吸作用、乙烯合成及其信号转导系统和果实软化等,并且它们与猕猴桃贮藏保鲜技术的研发与应用密切相关。本文重点从这3个方面就国内外相关研究进展进行综述,并讨论它们对猕猴桃耐贮性的影响,以期为猕猴桃耐贮新品种的培育和贮藏保鲜技术的研发提供理论依据。     

Storage of 'Gloster 69' apples in the preclimacteric state for up to 200 days after harvest

'Gloster 69' apples are unusual because they do not accumulate ethylene during storage at 2 kPa O₂ at 1.5–3.5°C with continuous ethylene removal. Their ethylene physiology and the extent of various ripening processes in storage were investigated. Ethylene production and l-aminocyclopropane-l-carboxylic acid (ACC) remained low for up to 200 days, and both increased on transfer of fruit to 15°C. The increase in ACC could be stimulated by ethylene treatment of apples after storage. In spite of this evidence that fruit remained preclimacteric, some softening and production of soluble pectin and volatile esters occurred at 3.5°C. These processes were suppressed at 1.5°C, but chlorophyll, starch, malate and sucrose losses and increases in glucose and fructose occurred at both temperatures.     

Isolation and characterization of a tomato non-specific lipid transfer protein involved in polygalacturonase-mediated pectin degradation

An important aspect of the ripening process of tomato fruit is softening. Softening is accompanied by hydrolysis of the pectin in the cell wall by pectinases, causing loss of cell adhesion in the middle lamella. One of the most significant pectin-degrading enzymes is polygalacturonase (PG). Previous reports have shown that PG in tomato may exist in different forms (PG1, PG2a, PG2b, and PGx) commonly referred to as PG isoenzymes. The gene product PG2 is differentially glycosylated and is thought to associate with other proteins to form PG1 and PGx. This association is thought to modulate its pectin-degrading activity in planta. An 8 kDa protein that is part of the tomato PG1 multiprotein complex has been isolated, purified, and functionally characterized. This protein, designated 'activator' (ACT), belongs to the class of non-specific lipid transfer proteins (nsLTPs). ACT is capable of 'converting' the gene product PG2 into a more active and heat-stable form, which increases PG-mediated pectin degradation in vitro and stimulates PG-mediated tissue breakdown in planta. This finding suggests a new, not previously identified, function for nsLTPs in the modification of hydrolytic enzyme activity. It is proposed that ACT plays a role in the modulation of PG activity during tomato fruit softening.     

Temporal Sequence of Cell Wall Disassembly in Rapidly Ripening Melon Fruit

The Charentais variety of melon (Cucumis melo cv Reticulatus F1 Alpha) was observed to undergo very rapid ripening, with the transition from the preripe to overripe stage occurring within 24 to 48 h. During this time, the flesh first softened and then exhibited substantial disintegration, suggesting that Charentais may represent a useful model system to examine the temporal sequence of changes in cell wall composition that typically take place in softening fruit. The total amount of pectin in the cell wall showed little reduction during ripening but its solubility changed substantially. Initial changes in pectin solubility coincided with a loss of galactose from tightly bound pectins, but preceded the expression of polygalacturonase (PG) mRNAs, suggesting early, PG-independent modification of pectin structure. Depolymerization of polyuronides occurred predominantly in the later ripening stages, and after the appearance of PG mRNAs, suggesting the existence of PG-dependent pectin degradation in later stages. Depolymerization of hemicelluloses was observed throughout ripening, and degradation of a tightly bound xyloglucan fraction was detected at the early onset of softening. Thus, metabolism of xyloglucan that may be closely associated with cellulose microfibrils may contribute to the initial stages of fruit softening. A model is presented of the temporal sequence of cell wall changes during cell wall disassembly in ripening Charentais melon.