Expression of genes encoding xyloglucan endotransglycosylase/hydrolase in ‘Saijo’ persimmon fruit during softening after deastringency treatment

Persimmon (Diospyros kaki Thunb.) fruit undergoes intensive cell wall modification during postharvest fruit softening. Xyloglucan metabolism is important in cell wall disassembly. We cloned cDNAs for two xyloglucan endotransglycosylase/hydrolase genes (DkXTH1 and DkXTH2) from ‘Saijo’ persimmon fruit treated with dry ice to remove astringency. In order to determine the ethylene dependence of XTH gene expression, fruit were exposed to 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, prior to removal of astringency. Ethylene production increased in mature control and 1-MCP-pretreated fruit after dry-ice treatment, and flesh firmness decreased to the same extent during dry-ice treatment in the control and 1-MCP-pretreated fruit. After dry-ice treatment, control fruit softened completely, but fruit firmness was maintained in 1-MCP-pretreated fruit. Accumulation of DkXTH1 mRNA was induced simultaneously with commencement of ethylene production in mature control fruit. Pretreatment with 1-MCP delayed accumulation of DkXTH1 mRNA. DkXTH2 expression also coincided with fruit softening but was intensified by 1-MCP treatment during the deastringency treatment. These results indicate that fruit softening was related to both DkXTH1 and DkXTH2 expression in ‘Saijo’ persimmons.     

Molecular analysis of softening and ethylene synthesis and signaling pathways in a non-softening apple cultivar, ‘Honeycrisp’ and a rapidly softening cultivar, ‘McIntosh’

A feature of ‘Honeycrisp’ apples [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.] is that they maintain flesh firmness over extended storage. The objective of this study was to elucidate molecular mechanisms that are responsible for slow softening of ‘Honeycrisp’ as compared with a rapidly softening cultivar, ‘McIntosh’. Fruit from both cultivars were picked during the normal harvest period and stored at 20 °C for 10 d. Internal ethylene concentrations (IECs) in ‘Honeycrisp’ fruit were lower than in ‘McIntosh’, but at climacteric levels of ethylene ‘Honeycrisp’ fruit maintained their firmness over this period, while ‘McIntosh’ softened rapidly. Concentrations of the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) were higher in ‘Honeycrisp’ than in ‘McIntosh’ apples. qRT-PCR analysis was carried out for genes involved in ethylene biosynthesis, perception and signaling [ACC synthase (MdACS); ACC oxidase (MdACO); ethylene receptors (MdETR and MdERS); constitutive triple response (MdCTR); ethylene response factor (MdERF)], as well as those involved in cell wall metabolism [polygalacturonase (MdPG); xyloglucan endotransglucosylase (MdXTH); expansin (MdEXP); β-galactosidase (Md β-GS); arabinofuranosidase (MdAFase); pectate lyase (MdPL)]. At comparable IECs, the expression of genes involved in ethylene synthesis, ethylene perception and signal transduction was generally much higher in ‘Honeycrisp’ than in ‘McIntosh’ fruit. However, the expression of MdAFase and MdEXP3 was generally lower in ‘Honeycrisp’ than in ‘McIntosh’, while that of MdPG and MdPL was extremely low in ‘Honeycrisp’. Expression of MdPG1 was very low, even though IECs were at climacteric levels. Absence of fruit softening in ‘Honeycrisp’ is probably associated with restricted cell wall enzyme activity. The lower maximum IECs found in ‘Honeycrisp’ compared with ‘McIntosh’ do not appear to be related to expression of genes involved in ethylene biosynthesis.     

采后嘎拉苹果果实细胞壁代谢及关键酶基因表达特性研究

以嘎拉苹果为试材,研究其果实细胞壁代谢及关键酶基因表达特性及受1-MCP、乙烯利和低温的影响效应。结果表明,常温下,嘎拉果实硬度变化与WSP显著正相关,与CSP和半纤维素显著负相关,与ISP的关系不大;1-MCP和低温处理显著抑制了WSP含量上升,减缓了CSP和半纤维素降解。嘎拉果实细胞壁酶中,β-Gal活性最高、增加最快,其基因表达亦迅速增加,α-L-Af活性和基因表达虽增加速率低于β-Gal,但二者变化规律相似,均显著受到1-MCP和0℃低温的抑制;PG和PME活性和基因表达量亦呈增加趋势,但未能完全被1-MCP处理和0℃低温所抑制;相关性分析表明,其细胞壁酶活性变化均与硬度呈显著负相关性,并显著受到1-MCP和低温的影响。但是,乙烯利处理虽对嘎拉果实软化有一定的促进作用,但效果不显著。     

Effect of heat treatments on gene expression and enzyme activities associated to cell wall degradation in strawberry fruit

Strawberries at white ripening stage were heat treated at 45 °C for 3 h in an air oven and then stored at 20 °C for 72 h. Firmness, activity of enzymes associated to cell wall degradation, and expression of related genes were determined during the storage. Fruit firmness decreased during the incubation time, and after 24 h of storage the heat-treated fruit softened less than the control fruit. However, after 3 days at 20 °C no differences in firmness were detected between control and heat-treated fruit. Immediately after heat treatment application, the activity of endo-1,4-β-d-glucanase (EGase), β-xylosidase and β-galactosidase decreased, while polygalacturonase activity remained at a level similar to the control fruit. However, lower activities of all these enzymes, including polygalacturonase, were detected in heat-treated fruit after 24 h at 20 °C. The enzyme activity of β-xylosidase, β-galactosidase and polygalacturonase increased after 72 h up to similar or higher values than those of controls. However, endo-1,4-β-d-glucanase activity remained lower in heat-treated samples even after 72 h at 20 °C. The expression of genes encoding endoglucanase (FaCel1), β-xylosidase (FaXyl1), polygalacturonase (FaPG1) and expansin (FaExp2) was reduced immediately after treatment and during the following 4 h, and then increased after 24 h to levels similar to or higher than those of control fruit.

Therefore, the selected treatment (45 °C, 3 h in air) effectively reduced strawberry softening and caused a temporary reduction of both the expression of above-mentioned genes and the activity of a set of enzymes involved in cell wall disassembly.     

Role of putrescine in regulating fruit softening and antioxidative enzyme systems in ‘Samar Bahisht Chaunsa’ mango

The role of putrescine (PUT) in regulating fruit softening, antioxidative enzymes and biochemical changes in fruit quality was investigated during ripening and cold storage of mango (Mangifera indica cv. Samar Bahisht Chaunsa). Fruit were treated with various PUT concentrations (0.0, 0.1, 1.0 and 2.0 mM) and were allowed to ripen at 32 ± 2 °C for 7 days, or stored at 11 ± 1 °C for up to 28 days. Respiration rate and ethylene production were measured daily during ripening and cold storage. Cell wall degrading enzymes such as exo-polygalacturonase (exo-PG), endo-polygalacturonase (endo-PG), pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), antioxidative enzymes including superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT), fruit firmness as well as biochemical fruit quality characteristics were estimated during ripening and cold storage at 2 and 7 day intervals, respectively. PUT treatments reduced respiration rate, ethylene production and maintained higher fruit firmness during ripening as well as cold storage. PUT-treated fruit exhibited significantly suppressed activities of cell wall enzymes (exo-, endo-PG and EGase), but retained higher PE activity during ripening and cold storage. Total phenolic and antioxidant contents were significantly higher in PUT-treated fruit during ripening as well in the cold storage period than in the controls. Activities of antioxidative enzymes (CAT, POX and SOD) were also significantly higher in PUT-treated fruit during ripening as well as cold storage. SSC and SSC:TA were lower in PUT-treated fruit, while TA and ascorbic acid content showed the reverse trend. In conclusion, pre-storage 2.0 mM PUT treatment inhibited ethylene production and suppressed the activities of cell wall enzymes, while resulting in higher activities of antioxidative enzymes and maintaining better fruit quality during ripening and cold storage.     

1-MCP结合自发气调包装对‘空心李’果实软化和细胞壁代谢的影响

探讨果实软化与细胞壁代谢之间的关系及1-甲基环丙烯(1-MCP)结合自发气调包装(MAP)对果实软化的调控机制,为生产中李果实软化问题提供理论依据和技术参考。笔者以贵州省特色果品‘空心李’为试材,通过测定果实的硬度、细胞壁代谢成分和细胞壁代谢酶活性的变化,研究1-MCP、MAP及两者结合(1-MCP+MAP)对(20±1)℃下果实软化的抑制效应。结果表明：（1）与对照（直接放于纸箱内）相比,1-MCP、MAP及1-MCP+MAP处理抑制了果实硬度下降,原果胶和纤维素降解,抑制了多聚半乳糖醛酸酶(PG)、果胶甲脂酶(PME)和纤维素酶(Cx)活性增加,抑制效果为1-MCP+MAP>1-MCP>MAP。（2）果实硬度的下降与原果胶和纤维素含量呈显著正相关,与可溶性果胶含量关系表现不一,1-MCP和1-MCP+MAP处理与可溶性果胶含量呈显著负相关,而对照和MAP处理与可溶性果胶含量没有表现出明显的相关性。1-MCP、MAP、1-MCP+MAP处理和对照果实硬度的下降与PG和PME活性存在显著负相关,对照和MAP处理的果实硬度与Cx活性表现显著负相关,1-MCP和1-MCP+MAP处理果实硬度与Cx活性没有表现相关性。1-MCP结合MAP对沿河‘空心李’果实硬度下降、细胞壁物质降解及其相关酶活性有显著抑制作用,能够抑制‘空心李’果实软化,延长保鲜时间,减少采后损失。     

Developmental changes in cell wall polysaccharides from sweet cherry (Prunus avium L.) cultivars with contrasting firmness

Firmness is a major quality attribute of fresh cherries, and is also a main factor affecting susceptibility to bruising and postharvest rots. In order to identify the factors determining the textural differences between genotypes, we evaluated the solubilization, depolymerization and monosaccharide composition of pectin and hemicelluloses from two cultivars with contrasting firmness (‘Sweetheart’, firm and ‘Newstar’, soft) at four different developmental stages. Firm ‘Sweetheart’ cherries had higher contents of cell wall material than soft ‘Newstar’ fruit. Moderate depolymerization of hemicellulose and tightly bound pectins was detected irrespective of cultivar firmness. The general pattern and extent of uronic acid solubilization was quite similar in both cultivars. Rhamnogalacturonan I (RG-I) seemed to be preferentially solubilized in firm ‘Sweetheart’ fruit as opposed to tightly bound homogalacturonans (HG) in soft cherries. Pectic polymers with higher neutral sugar to uronic acids ratio were found from early development in soft ‘Newstar’ fruit. Overall, soft ‘Newstar’ fruit had reduced wall content and higher branching of tightly bound pectins than firm ‘Sweetheart’ fruit. These factors may be associated with the varietal differences in cherry firmness.     

Improving storability of persimmon cv. Rojo Brillante by combined use of preharvest and postharvest treatments

The combined use of preharvest treatments, gibberellic acid (GA₃) or calcium nitrate, with 1-methylcyclopropene (1-MCP) treatment applied postharvest, was evaluated to improve the storability of ‘Rojo Brillante’ persimmon fruit, at both 1 and 15 °C. Properties linked to commercial quality, such as flesh firmness, external colour, total soluble solids and level of astringency, were evaluated at harvest, periodically during storage, as well as after subsequent shelf-life periods. At both storage temperatures, control fruit and calcium nitrate-treated fruit showed commercial quality for 20 d; the sole application of GA₃ delayed loss of firmness for 30 d while the treatment with 1-MCP by itself allowed storage of the fruit for 40 d. The combined use of calcium nitrate plus 1-MCP did not improve maintenance of quality any more than when 1-MCP was applied alone. The combination of GA₃ and 1-MCP delayed the symptoms of chilling injury, extending the storability at 1 °C for up to nearly 3 months. During storage at 15 °C, the combination of both treatments resulted in high-firmness values for 30 d, but did not prolong the storage period any longer than the 40 d reached by the sole application of 1-MCP. Irrespective of treatment, a loss of efficacy of the deastringency treatment was observed after 30 d of storage at 15 °C.     

Biochemical and physiological study of the firmness of table grape berries

Firmness is an essential quality parameter of table grapes (Vitis vinifera) for consumers, with grape bunches that contains soft berries less preferred, resulting in a reduction in the market price. The softening of grape berries has been commonly associated with cell walls, especially the disassembly of pectic polysaccharides. However, the process of berry softening is not completely understood. To investigate the softening process of grape berries, we compared the Thompson Seedless variety, which suffers significant economic losses due to fruit softening, and NN107, a new variety with a significantly higher level of berry firmness. The composition of the cell wall during the berry development of these two grape varieties was compared. NN107 berries had a greater amount of calcium and uronic acids in the cell wall material than Thompson Seedless grapes, suggesting a special role for calcium bridge formation in NN107. Additionally, polyacrylamide carbohydrate electrophoresis (PACE) analysis suggested differences between these varieties in pectin structure. Thompson Seedless grapes showed increased pectolyase hydrolysable site dynamics in the cell wall material and higher polygalacturonase activity than NN107. Immunohistochemistry focusing on the pectin structure confirmed the roles of both calcium bridge formation and cell wall integrity as they relate to a firmer grape berry phenotype.     

Patterns of enzymatic activity of cell wall-modifying enzymes during growth and ripening of apples

Fruit softening is thought to result from extensive cell wall modifications that occur during ripening. These modifications are the result, at least in part, of the activity of members of cell wall-modifying enzymes from the same families involved in the cell wall loosening which promote tissue extension and growth. In this work, the activities of a set of pectolytic and non-pectolytic cell wall-modifying enzymes, namely polygalacturonase (PG; endo-and exo-acting), pectin methylesterase (PME), pectate lyase (PL), β-galactosidase (β-Gal), α-l-arabinofuranosidase (AFase), endo-1,4-β-glucanase (EGase), xyloglucan endotransglycosylase (XET) and expansin, were monitored during growth and ripening of ‘Mondial Gala’ apple (Malus × domestica Borkh.) fruit. After optimisation of protein extraction protocols and standard activity assays, activity could be detected in all the assays, except for endo-PG. The overall results suggest that fruit growth and ripening are possibly coordinated by members of the same families of cell wall-modifying enzymes, although different isoforms may be involved in distinct developmental processes. Based on the trend of total activity measured in vitro using equal amounts of protein per developmental stage, the role of EGase seems to be more prominent during growth than during ripening, and XET activity is most important only after the fruit stopped growing and is maintained throughout ripening. β-Gal and AFase activities increased after harvest as the fruit became over-ripe. On the other hand, exo-PG, PL and expansin activities increase from that in unripe fruit to fruit at harvest but are maintained at similar levels thereafter, throughout the over-ripe stages. The patterns of activity observed are discussed in relation to published information about ripening of apples and to results reported using other species.     

Maturity assessment at harvest and prediction of softening in a late maturing nectarine cultivar after cold storage

The absorption coefficient μ_a measured at 670 nm in fruit pulp at harvest by time-resolved reflectance spectroscopy (TRS) has been shown to be a good maturity index for early nectarine cultivars. By including individual fruit maturity as a biological shift factor (BSF) into a kinetic model for softening it is possible to select fruit with different shelf-life potential. The BSF approach combined with TRS measurement and kinetic modeling of firmness was applied to a late maturing nectarine cultivar (‘Morsiani 90’), ripened at 20 °C after harvest or after storage at 0 °C and 4 °C, the latter conditions inducing chilling injury. At harvest the absorption coefficient μ_a had low values and low variability, indicating advanced maturity, while firmness was similar to that of early cultivars. The softening model took into account these differences, showing parameters similar to those of the early cultivars with the exception of the softening rate which was 2-6 times lower, indicating a slower softening in ‘Morsiani 90’ fruit. Decay of μ_a at 20 °C was also slower. Softening continued during storage at 4 °C, but not at 0 °C. After storage at 0 °C softening was resumed similarly to non-stored fruit, but with much variability. Fruit stored at 4 °C, which showed chilling injury, had a softening rate at 20 °C significantly higher than that of 0 °C fruit. It is suggested that the same changes in cell wall metabolism which induce the appearance of chilling injury also affect firmness and increase softening rate.     

Effectiveness of pre- and post-veraison calcium applications to control decay and maintain table grape fruit quality during storage

A two year research was carried out on a table grape vineyard, cv. Italia, to evaluate the effectiveness of pre- and post-veraison calcium applications for controlling postharvest table grape rots and maintaining high fruit quality during cold storage. Two calcium application timings (from fruit set to veraison and from veraison to harvest) were compared to an untreated control. Clusters were sprayed with calcium chloride as Ca EDTA 44%. After each calcium application, bunch samples were collected and Ca²⁺ concentration was measured in berry compartments (skin, flesh and seeds). The main mechanical and chemical characteristics were measured on bunch samples at harvesting and during storage. In addition, the incidence of Botrytis cinerea rots, computed as McKinney index, was evaluated in field on natural inoculum and after harvesting on bunches artificially inoculated and maintained at room temperature. The highest Ca²⁺ concentrations were detected in skin tissues and after pre-veraison applications. Calcium accumulation in skin and flesh tissues stopped after veraison, whereas it continued up to ripening in seeds since the axial flow, differently from the peripheral, remains functional. In both years, calcium applications to bunches were effective both in maintaining postharvest fruit quality, as shown by flesh firmness and berry breaking force, and in reducing B. cinerea rots during storage. The applications were particularly efficacious if carried out between fruit set and veraison when stomata are functional and the re-translocation of calcium not directly absorbed by the bunches may occur via xylem transport.     

1-MCP对采后‘红心’番石榴果实软化的影响

为了从细胞壁代谢角度研究1-甲基环丙烯(1-MCP)调控采后番石榴果实软化的机制,用1 μL/L 1-MCP处理‘红心’番石榴果实试材。通过测定果实的硬度、细胞壁代谢相关物质及相关酶活性的变化,研究1-MCP处理对常温(25±1℃)贮藏下番石榴果实软化的抑制作用。结果表明,1 μL/L 1-MCP处理使采后番石榴果实的硬度比对照组果实高0.51倍,并有效抑制多聚半乳糖醛酸酶、果胶甲酯酶、纤维素酶、β-葡萄糖苷酶、α-淀粉酶和β-淀粉酶的活性,减缓可溶性果胶、葡萄糖含量的增加,延缓原果胶、纤维素和淀粉含量在采后贮藏期间的下降。因此,1 μL/L 1-MCP处理能有效延缓采后‘红心’番石榴的软化进程,延长其采后贮运保鲜期。     

Pericarp tissue microstructure and cell wall polysaccharide chemistry are differently affected in lines of tomato with contrasted firmness

The contribution of tissue histology and cell wall polysaccharides chemistry to describing ripe tomato fruit texture was addressed in near isogenic lines of fruits harboring firmness QTL. These lines were constructed in Levovil (L), VilB (B), M82 (P) and Moneyberg (Mbg) genetic backgrounds and carried introgressed fragments from three origins on chromosomes 2, 3, 4, 5 or 9 (and two sub-regions a and b). The firmness of their pericarp tissue was measured by compression testing and related to cell size distribution and to published data on their cell wall polysaccharide chemistry. The pericarp tissue from all L9 lines, B9 and P3.4 was firmer than the respective parental line while that from Mbg9 and P9.2.5 was softer. The pericarp tissue from L4, L4a and Mbg5 fruit was made of larger cells while that from Mbg2 and Mbg9 had smaller cells than their parents. Correlations were found between firmness and cell size distribution for QTLs only in the Levovil group. Correlations between firmness, histological characteristics and cell wall polysaccharide chemistry indicate positive relations between glucose-containing polysaccharide (cellulose and hemicelluloses) contents and pericarp tissue thickness. Other positive relations were found between galactosylated pectins and hemicelluloses and firmness in QTL lines of the Levovil background. The results show that chromosomes 9, 5, 4 and 2 are associated with pericarp histology in these lines and that pericarp tissue firmness depends on histology and cell wall chemistry according to genetics. These tomato lines represent good models to study the complex contributions of turgor pressure, cell wall chemistry, tissue architecture and their mechanisms of modulation underpinning texture in ripening tomatoes.     

Repeated treatment of apple fruit with 1-methylcyclopropene (1-MCP) prior to controlled atmosphere storage

The effect of multiple 1-MCP treatments prior to the establishment of controlled atmosphere (CA) storage on the quality of ‘McIntosh’ and ‘Empire’ apples [Malus × sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] was investigated. Fruit were harvested on three occasions over a 1 week period, and at each harvest cooled overnight and 1-MCP applied the following day. Fruit from the first or second harvests were treated again or for the first time when fruit from each successive harvest was treated. CA conditions were established after the last 1-MCP treatment and fruit were stored for up to 8 months. Delays in 1-MCP application generally resulted in progressively higher internal ethylene concentrations (IECs) at the time of treatment and lower firmness both at the time of treatment and after storage. Multiple 1-MCP applications kept IECs low and maintained firmness compared with single applications that were applied after 4 d. For ‘McIntosh’, external CO₂ injury was more prevalent after storage if fruit were treated without delays after harvest for earlier harvests while later harvests were less affected. For ‘Empire’, flesh browning was more prevalent in fruit from later harvests and 1-MCP treated fruit had higher levels than untreated fruit. Either early 1-MCP treatment or multiple treatments reduced senescent breakdown in ‘McIntosh’, and core browning and greasiness in ‘Empire’.     

Effect of calcium dips and chitosan coatings on postharvest life of strawberries (Fragaria x ananassa)

Strawberries (Fragaria x ananassa Duch.) were treated either with 1% calcium gluconate dips, 1.5% chitosan coatings or with a coating formulation containing 1.5% chitosan + 1% calcium gluconate and stored at 20 °C for up to 4 days. The effectiveness of the treatments was assessed by evaluating their impact on the following parameters: fungal decay incidence, loss of weight, firmness, external color, pH, titratable acidity and soluble solids content. Calcium dips were effective in decreasing surface damage and delaying both fungal decay and loss of firmness compared to untreated fruit. No sign of fungal decay was observed in fruit coated with 1.5% chitosan which also reduced fruit weight loss. Chitosan coatings markedly slowed the ripening of strawberries as shown by their retention of firmness and delayed changes in their external color. To a lesser extent titratable acidity and pH were also affected by coatings. Whilst addition of calcium gluconate to the chitosan coating formulation did not further extend the shelf-life of the fruit, the amount of calcium retained by strawberries was greater than that obtained with calcium dips alone, thus resulting in increased nutritional value of the strawberries.     

Effect of harvest maturity and cold storage on correlations between fruit properties during ripening of apricot (Prunus armeniaca)

Apricots (Prunus armeniaca) were held in air storage at 0 °C and ripened at 20 °C, or ripened at 20 °C straight after harvest, and changes in fruit quality quantified using postharvest and sensory evaluations. Maturity at harvest significantly affected flesh firmness and other quality factors. Mealiness and gel formation only developed in fruit that had been stored at low (0 °C) temperatures. Mealiness did not develop until firmness dropped below approximately 20 N, whereas gel formation began to develop when firmness was as high as 35 N. Development of mealiness and loss of juiciness were correlated; however, slight mealiness was perceived when fruit were still considered juicy. Specific cultivar-related differences were evident in the changes in firmness and development of gel formation during and after cold storage. Fruit were less liked by the sensory panel when firmness dropped below 20 N, as juiciness decreased and mealiness and gel formation increased. Cell wall studies showed changes in yields of water-soluble and CDTA (trans-1,2-cyclohexanediamine tetraacetic acid)-soluble pectin. In fruit ripened after cold storage, mealiness and gel formation was accompanied by an increase in water-soluble pectin and an increase in CDTA-soluble pectin, whereas in apricots ripened straight after harvest, water-soluble pectin increased but CDTA-soluble pectin slightly decreased. All fruit, regardless of maturity or having chilling disorders or not, fitted the same correlation between firmness and uronic acid content of water-soluble pectin, but no pattern was evident for CDTA-soluble pectin. We concluded that the increasing solubilisation of pectin was a major feature of fruit softening in apricot, whereas the differences in CDTA-soluble pectin may reflect differences in strength of cell adhesion.     

金秋梨幼果期钙处理对果实衰老相关生理的影响

以金秋梨为试材,采用对比试验,研究了幼果喷钙对金秋梨果实冷藏期间生理特性的影响,分析了钙对金秋梨采后生理变化的调节机制。结果表明,钙处理对提高果实钙含量和硬度有明显效应,降低了贮藏期间发病率,显著抑制超氧化物歧化酶（SOD）、过氧化物酶（POD）和过氧化氢酶（CAT）活性的降低,显著降低果实膜透性和减少丙二醛（MDA）含量,从而降低果实贮藏期间膜脂过氧化作用,延缓果实后熟衰老。配施萘乙酸（NAA）可增强喷钙效果。     

Mode of action of nitric oxide in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of ‘Kensington Pride’ mango

The mode of action of nitric oxide (NO) in inhibiting ethylene biosynthesis and fruit softening during ripening and cool storage of mango fruit was investigated. Hard mature green mango (Mangifera indica L. cv. ‘Kensington Pride’) fruit were fumigated with 20 μL L⁻¹ NO for 2 h at 21 °C and allowed to ripen at 21 ± 1 °C for 10 d, or stored at 13 ± 1 °C for 21 d. During ripening and cool storage, ethylene production and respiration rate from whole fruit were determined daily. The 1-aminocyclopropane-1-carboxylic acid (ACC) content, activities of ACC synthase (ACS), ACC oxidase (ACO), and fruit softening enzymes such as pectin esterase (PE), endo-1,4-β-d-glucanase (EGase), exo- and endo-polygalacturonase (exo-PG, endo-PG) as well as firmness and rheological properties of pulp were determined at two- and seven-day intervals during ripening and cool storage, respectively. NO fumigation inhibited ethylene biosynthesis and respiration rate, and maintained higher pulp firmness, springiness, cohesiveness, chewiness, adhesiveness, and stiffness. NO-fumigated fruit during cool storage and ripening had lower ACC contents through inhibiting the activities of both ACS and ACO in the fruit pulp. NO-fumigated fruit showed decreased activities of exo-PG, endo-PG, EGase, but maintained higher PE activity in pulp tissues during ripening and cool storage. In conclusion, NO fumigation inhibited ethylene biosynthesis through inhibition of ACS and ACO activities leading to reduced ACC content in the fruit pulp which consequently, reduced the activities of fruit softening enzymes during ripening and cool storage.