Modification of polyuronides and hemicelluloses during muskmelon fruit softening

The loss of flesh firmness during muskmelon ( Cucumis melo var. reticulatus L. Naud. cv. Galia) fruit ripening was related temporally to modifications of pectic and hemicellulosic polysaccharides, and a net loss of non-cellulosic neutral sugars. An increase in solubility and a decrease in molecular size of polyuronides occurred during ripening; however, the decrease in molecular size was apparently not the result of polygalacturonase (EC 3.2.1.15) activity. Molecular size of hemicelluloses shifted from larger to smaller polymers during ripening, and this decrease was accompanied by changes in neutral sugar composition. Galactose, glucose, and xylose were the predominant neutral sugars in the hemicellulosic polymers. On a mol% basis there were decreases in galactose and glucose in large hemicellulosic polymers with ripening. Relative xylose content approximately doubled in the large polymers during ripening; xylose was the predominant neutral sugar in the small polymers and remained fairly constant.     

Proteomic analysis of differentially accumulated proteins during ripening and in response to 1-MCP in papaya fruit

Papaya (Carica papaya L.) is a climacteric fruit susceptible to postharvest losses due to the ethylene-induced ripening. The inhibitor of ethylene action, 1-methylcyclopropene (1-MCP), has been used worldwide as a safe postharvest non-toxic agent, but the physiological and biochemical modifications induced by 1-MCP are not well understood. Using the 2-DE analysis, we report the changes in the protein profiles after 6 and 18 days of postharvest and the effect of the effect of 1-MCP treatment on fruits. Twenty seven protein spots showing differences in abundance during ripening were successfully identified by nano-LC-ESI/MS/MS. Some spots corresponded to the cell wall degrading enzymes related to fruit ripening; others were involved in oxidative damage protection, protein folding, and cell growth and survival that were induced by 1-MCP. This is the first proteomic report analyzing the effect of 1-MCP in papaya ripening. The present data will help to shed light on papaya fruit ripening process.     

Papaya fruit softening, endoxylanase gene expression, protein and activity

Papaya ( Carica papaya L.) cell wall matrix polysaccharides are modified as the fruit starts to soften during ripening and an endoxylanase is expressed that may play a role in the softening process. Endoxylanase gene expression, protein amount and activity were determined in papaya cultivars that differ in softening pattern and in one cultivar where softening was modified by the ethylene receptor inhibitor 1-methylcyclopropene (1-MCP). Antibodies to the endoxylanase catalytic domain were used to determine protein accumulation. The three papaya varieties used in the study, 'Line 8', 'Sunset', and 'Line 4-16', differed in softening pattern, respiration rate, ethylene production and showed similar parallel relationships during ripening and softening in endoxylanase expression, protein level and activity. When fruit of the three papaya varieties showed the respiratory climacteric and started to soften, the level of endoxylanase gene expression increased and this increase was related to the amount of endoxylanase protein at 32 kDa and its activity. Fruit when treated at less than 10% skin yellow stage with 1-MCP showed a significant delay in the respiratory climacteric and softening, and reduced ethylene production, and when ripe was firmer and had a 'rubbery' texture. The 1-MCP-treated fruit that had the 'rubbery' texture showed suppressed endoxylanase gene expression, protein and enzymatic activity. Little or no delay occurred between endoxylanase gene expression and the appearance of activity during posttranslational processing from 65 to 32 kDa. The close relationship between endoxylanase gene expression, protein accumulation and activity in different varieties and the failure of the 1-MCP-treated fruit to fully soften, supported de novo synthesis of endoxylanase, rapid posttranslation processing and a role in papaya fruit softening.     

Characterization of expression, and cloning, of beta-D-xylosidase and alpha-L-arabinofuranosidase in developing and ripening tomato (Lycopersicon esculentum Mill.) fruit

Modifications to the cell wall of developing and ripening tomato fruit are mediated by cell wall-degrading enzymes, including a beta-d-xylosidase or alpha-l-arabinofuranosidase, which participate in the breakdown of xylans and/or arabinoxylans. The activity of both enzymes was highest during early fruit growth, before decreasing during later development and ripening. Two beta-d-xylosidase cDNAs, designated LeXYL1 and LeXYL2, and an alpha-l-arabinofuranosidase cDNA, designated LeARF1, were obtained. Accumulation of mRNAs for beta-d-xylosidase and alpha-l-arabinofuranosidase was examined during fruit development and ripening. LeARF1 and LeXYL2 genes were relatively highly expressed during fruit development and decreased after the onset of ripening. By contrast, LeXYL1 was not expressed during fruit development, but was expressed later, particularly during over-ripening. The expression of all three genes was also followed in ripening-impaired mutants, Nr, Nr2, nor, and rin of cv. Ailsa Craig fruit. LeXYL2 mRNA was detected in the ripe fruits of all the mutants and its abundance was similar to that in mature green wild-type fruit. By contrast, LEXYL1 mRNA was expressed only in the ripe fruits of the Nr mutant, suggesting that the two beta-d-xylosidase genes are subject to distinct regulatory control during fruit development and ripening. LeARF1 mRNA was detected in ripe fruits of Nr2, nor and rin, and not in ripe fruit of the Nr mutant. The accumulation of LeARF1 in ripe fruit was restored by 1-methylcyclopropene (1-MCP), an inhibitor of ethylene action, while 1-MCP had no effect on the expression of LeXYL1 or LeXYL2. This suggests that LeARF1 expression is subject to negative regulation by ethylene and that the two beta-d-xylosidase genes are independent of ethylene action.     

Polyuronides in Avocado (Persea americana) and Tomato (Lycopersicon esculentum) Fruits Exhibit Markedly Different Patterns of Molecular Weight Downshifts during Ripening

Avocado (Persea americana) fruit experience a rapid and extensive loss of firmness during ripening. In this study, we examined whether the chelator solubility and molecular weight of avocado polyuronides paralleled the accumulation of polygalacturonase (PG) activity and loss in fruit firmness. Polyuronides were derived from ethanolic precipitates of avocado mesocarp prepared using a procedure to rapidly inactivate endogenous enzymes. During ripening, chelator (cyclohexane-trans-1,2-diamine tetraacetic acid [CDTA])-soluble polyuronides increased from approximately 30 to 40 [mu]g of galacturonic acid equivalents (mg alcohol-insoluble solids)-1 in preripe fruit to 150 to 170 [mu]g mg-1 in postclimacteric fruit. In preripe fruit, chelator-extractable polyuronides were of high molecular weight and were partially excluded from Sepharose CL- 2B-300 gel filtration media. Avocado polyuronides exhibited marked downshifts in molecular weight during ripening. At the postclimacteric stage, nearly all chelator-extractable polyuronides, which constituted from 75 to 90% of total cell wall uronic acid content, eluted near the total volume of the filtration media. Rechromatography of low molecular weight polyuronides on Bio-Gel P-4 disclosed that oligomeric uronic acids are produced in vivo during avocado ripening. The gel filtration behavior and pattern of depolymerization of avocado polyuronides were not influenced by the polyuronide extraction protocol (imidazole versus CDTA) or by chromatographic conditions designed to minimize interpolymeric aggregation. Polyuronides from ripening tomato (Lycopersicon esculentum) fruit extracted and chromatographed under conditions identical with those used for avocado polyuronides exhibited markedly less rapid and less extensive downshifts in molecular weight during the transition from mature-green to fully ripe. Even during a 9-d period beyond the fully ripe stage, tomato fruit polyuronides exhibited limited additional depolymerization and did not include oligomeric species. A comparison of the data for the avocado and tomato fruit indicates that downshifts in polyuronide molecular weight are a prominent feature of avocado ripening and may also explain why molecular down-regulation of PG (EC 3.2.1.15) in tomato fruit has resulted in minimal effects on fruit performance until the terminal stages of ripening.     

Papaya Fruit Softening: Role of Hydrolases

Papaya (Carica papaya L.) cultivars show a wide variation in fruit softening rates, a character that determines fruit quality and shelf life, and thought to be the result of cell wall degradation. The activity of pectin methylesterase, β-galactosidase, endoglucanase, endoxylanase and xylosidase were correlated with normal softening, though no relationship was found between polygalacturonase activity and softening. When softening was modified by 1-MCP treatment, a delay occurred before the normal increase in activities of all cell wall activities except endoxylanase which was completely suppressed. Significant cell wall mass loss occurred in the mesocarp tissue during normal softening, but did not occur to the same extent following 1-MCP treatment. During normal softening, pectin polysaccharides and loosely bound matrix polysaccharides were solubilized and the release of xylosyl and galactosyl residues occurred. Cell wall changes in galactosyl residues after 1-MCP treatment were comparable to those of untreated fruit but 1-MCP treated fruit did not soften completely. The changes in the cell wall fractions containing xylosyl residues in 1-MCP treated fruit showed less solubilization and a higher association of xylosyl residues with the pectic polysaccharides. The results indicated that normal modification of cell wall xylosyl components during ripening did not occur following 1-MCP treatment at the color-break stage, this was associated with the failure of these fruit to fully soften and a selective suppression of endoxylanase activity. The results support a role for endoxylanase in normal papaya fruit softening and its suppression by 1-MCP lead to a failure to fully soften. Normal papaya ripening related softening was dependent upon the expression and activity of endoglucanase, β-galactosidase and endoxylanase.     

Inhibition of the ethylene response by 1-MCP in tomato suggests that polyamines are not involved in delaying ripening, but may moderate the rate of ripening or over-ripening

Ethylene initiates the ripening and senescence of climacteric fruit, whereas polyamines have been considered as senescence inhibitors. Ethylene and polyamine biosynthetic pathways share S-adenosylmethionine as a common intermediate. The effects of 1-methylcyclopropene (1-MCP), an inhibitor of ethylene perception, on ethylene and polyamine metabolism and associated gene expression was investigated during ripening of the model climacteric fruit, tomato (Solanum lycopersicum L.), to determine whether its effect could be via polyamines as well as through a direct effect on ethylene. 1-MCP delayed ripening for 8 d compared with control fruit, similarly delaying ethylene production and the expression of 1-aminocyclopropane-1-carboxylic acid (ACC)-synthase and some ethylene receptor genes, but not that of ACC oxidase. The expression of ethylene receptor genes returned as ripening was reinitiated. Free putrescine contents remained low while ripening was inhibited by 1-MCP, but increased when the fruit started to ripen; bound putrescine contents were lower. The activity of the putrescine biosynthetic enzyme, arginine decarboxylase, was higher in 1-MCP-treated fruit. Activity of S-adenosylmethionine-decarboxylase peaked at the same time as putrescine levels in control and treated fruit. Gene expression for arginine decarboxylase peaked early in non-treated fruit and coincident with the delayed peak in putrescine in treated fruit. A coincident peak in the gene expression for arginase, S-adenosylmethionine-decarboxylase, and spermidine and spermine synthases was also seen in treated fruit. No effect of treatment on ornithine decarboxylase activity was detected. Polyamines are thus not directly associated with a delay in tomato fruit ripening, but may prolong the fully-ripe stage before the fruit tissues undergo senescence.     

Ethylene action blockade and cold storage affect ripening of ‘Golden’ papaya fruit

The purpose of this work was to evaluate the effects of ethylene action blockade and cold storage on the ripening of ‘Golden’ papaya fruit. Papayas harvested at maturity stage 1 (up to 15% yellow skin) were evaluated. Half of the fruits, whether treated or not treated with 100 nL L⁻¹ of 1-methylcyclopropene (1-MCP), were stored at 23°C, while the other half were stored at 11°C for 20 days prior to being stored at 23°C. Non-refrigerated fruits receiving 1-MCP application presented a reduction in respiratory activity, ethylene production, skin color development and pectinmethylesterase activity. Even with a gradual increase in ethylene production at 23°C, fruits treated with 1-MCP maintained a high firmness, but presented a loss of green skin color. Cold storage caused a decrease in ethylene production when fruits were transferred to 23°C. The results suggest that pulp softening is more dependent on ethylene than skin color development, and that some processes responsible for loss of firmness do not depend on ethylene.     

Responses of banana fruit to treatment with 1-methylcyclopropene

Experiments were conducted to determine levels of 1-methylcyclopropene (1-MCP) exposure needed to prevent ethylene-stimulated banana fruit ripening, characterise responses of ethylene-treated fruit to subsequent treatment with 1-MCP, and to test effects of subsequent ethylene treatment on 1-MCP-treated fruit softening. Fruit softening was measured at 20°C and 90% relative humidity. One hour exposure at 20°C to 1000 nl 1-MCP/l essentially eliminated ethylene-stimulated ripening effects. Exposure for 12 h at 20°C to just 50 nl 1-MCP/l was similarly effective. Fruit ripening initiated by ethylene treatment could also be delayed with subsequent 1-MCP treatment. However, 1-MCP treatment only slowed down ripening of ethylene-treated fruit when applied at 1 day after ethylene and was ineffective when applied 3 or 5 days after ethylene treatment. The ripening response of fruit treated with 1-MCP and subsequently treated with ethylene varied with interval time between 1-MCP and ethylene treatments. As time increased, the response of 1-MCP-treated fruit to ethylene was enhanced. Responses to 0.1, 1, 10 or 100 µl ethylene/l concentrations were similar. Enzyme kinetic analysis applied to 1-MCP effects on ethylene-induced softening of banana fruit suggested that 1-MCP inhibition is by noncompetitive antagonism of ethylene binding.     

Extensive solubilization and depolymerization of cell wall polysaccharides during avocado (Perseaamericana) ripening involves concerted action of polygalacturonase and pectinmethylesterase

During the ripening of avocado ( Persea americana Mill.) fruit, water-soluble polyuronides increased dramatically, concomitant with marked downshifts in molecular mass. Treatment of cell walls from pre-ripe fruit with purified avocado polygalacturonase (PG, EC 3.2.1.15) promoted the release and molecular mass downshift of polyuronides. The polyuronides released by PG were similar in size distribution to water-soluble polyuronides from fruit at intermediate stages of ripening. Polyuronides released from pre-ripe fruit by PG, although of relatively high molecular mass, were not further degraded upon additional incubation with fresh enzyme. Similarly, water-soluble polyuronides prepared from fruit at intermediate stages of ripening were largely resistant to the action of purified PG in vitro. When polyuronides derived from fruit at intermediate stages of ripening were treated with weak alkali or pectinmethylesterase (PME, EC 3.1.1.11), extensive molecular mass downshifts occurred in response to incubation with PG. These results suggest that PG plays the central role in polyuronide degradation in ripening avocado fruit cell walls and that partial de-esterification is necessary for the increase in the susceptibility of polyuronides to PG. Differences in the patterns of polyuronide depolymerization in avocado fruit compared with the more thoroughly characterized tomato fruit are discussed.     

Regulatory mechanisms of ethylene biosynthesis in response to various stimuli during maturation and ripening in fig fruit (Ficus carica L.).

In order to obtain a greater uniformity of maturation, the growth of the fig fruit (Ficus carica L.) can be stimulated by the application of either olive oil, ethrel/ethephon or auxin. The three treatments induce ethylene production in figs. In this study, we investigated the regulatory mechanisms responsible for oil, auxin and ethylene induced ethylene production in figs. The ethylene production in response to olive oil, auxin, and propylene treatments and during ripening were all induced by 1-methylcyclopropene (1-MCP) and inhibited by propylene indicating a negative feedback regulation mechanism. Three 1-aminocyclopropane-1-carboxylic acid (ACC) synthase genes (Fc-ACS1, Fc-ACS2 and Fc-ACS3) and one ACC oxidase gene (Fc-ACO1) were isolated and their expression patterns in response to either oil, propylene or auxin treatment in figs determined. The expression patterns of Fc-ACS1 and Fc-ACO1 were clearly inhibited by 1-MCP and induced by propylene in oil treated and ripe fruits indicating positive regulation by ethylene, whereas Fc-ACS2 gene expression was induced by 1-MCP and inhibited by propylene indicating negative regulation by ethylene. The Fc-ACS3 mRNA showed high level accumulation in the auxin treated fruit. The inhibition of Fc-ACS3 gene by 1-MCP in oil treated and in ripe fruits suggests that auxin and ethylene modulate the expression of this gene by multi-responsive signal transduction pathway mechanisms. We further report that the olive oil-induced ethylene in figs involves the ACC-dependent pathway and that multiple ethylene regulatory pathways are involved during maturation and ripening in figs and each specific pathway depends on the inducer/stimulus.     

Ozone-induced inhibition of kiwifruit ripening is amplified by 1-methylcyclopropene and reversed by exogenous ethylene

Background

Understanding the mechanisms involved in climacteric fruit ripening is key to improve fruit harvest quality and postharvest performance. Kiwifruit (Actinidia deliciosa cv. ‘Hayward’) ripening involves a series of metabolic changes regulated by ethylene. Although 1-methylcyclopropene (1-MCP, inhibitor of ethylene action) or ozone (O₃) exposure suppresses ethylene-related kiwifruit ripening, how these molecules interact during ripening is unknown.

Results

Harvested ‘Hayward’ kiwifruits were treated with 1-MCP and exposed to ethylene-free cold storage (0?°C, RH 95%) with ambient atmosphere (control) or atmosphere enriched with O₃ (0.3?μL?L^??1) for up to 6?months. Their subsequent ripening performance at 20?°C (90% RH) was characterized. Treatment with either 1-MCP or O₃ inhibited endogenous ethylene biosynthesis and delayed fruit ripening at 20?°C. 1-MCP and O₃ in combination severely inhibited kiwifruit ripening, significantly extending fruit storage potential. To characterize ethylene sensitivity of kiwifruit following 1-MCP and O₃ treatments, fruit were exposed to exogenous ethylene (100?μL?L^??1, 24?h) upon transfer to 20?°C following 4 and 6?months of cold storage. Exogenous ethylene treatment restored ethylene biosynthesis in fruit previously exposed in an O₃-enriched atmosphere. Comparative proteomics analysis showed separate kiwifruit ripening responses, unraveled common 1-MCP- and O₃-dependent metabolic pathways and identified specific proteins associated with these different ripening behaviors. Protein components that were differentially expressed following exogenous ethylene exposure after 1-MCP or O₃ treatment were identified and their protein-protein interaction networks were determined. The expression of several kiwifruit ripening related genes, such as 1-aminocyclopropane-1-carboxylic acid oxidase (ACO1), ethylene receptor (ETR1), lipoxygenase (LOX1), geranylgeranyl diphosphate synthase (GGP1), and expansin (EXP2), was strongly affected by O₃, 1-MCP, their combination, and exogenously applied ethylene.

Conclusions

Our findings suggest that the combination of 1-MCP and O₃ functions as a robust repressive modulator of kiwifruit ripening and provide new insight into the metabolic events underlying ethylene-induced and ethylene-independent ripening outcomes.

     

Effects of Chilling Temperatures on Ethylene Binding by Banana Fruit

Banana fruit are highly susceptible to chilling injury during low temperature storage. Experiments were conducted to compare ethylene binding during storage at chilling (3 and 8 °C) versus optimum (13 °C) temperatures. The skins of fruit stored at 3 and 8 °C gradually darkened as storage duration increased. This chilling effect was reflected in increasing membrane permeability as shown by increased relative electrolyte leakage from skin tissue. In contrast, banana fruit stored for 8 days at 13 °C showed no chilling injury symptoms. Exposure of banana fruit to the ethylene binding inhibitor 1-methylcyclopropene (1 l l^-1 1-MCP) prevented ripening. However, this treatment also enhanced the chilling injury accelerated the occurrence of chilling injury-associated increased membrane permeability. ¹⁴C-ethylene release assay showed that ethylene binding by banana fruit stored at low temperature decreased with reduced storage temperature and/or prolonged storage time. Fruit exposed to 1-MCP for 12 h and then stored at 3 or 8 °C exhibited lower ethylene binding than those stored at 13 °C. Thus, chilling injury of banana fruit stored at low temperature is associated with a decrease in ethylene binding. The ability of tissue to respond to ethylene is evidently reduced, thereby resulting in failure to ripen.     

Papaya beta-galactosidase/galactanase isoforms in differential cell wall hydrolysis and fruit softening during ripening.

The potential significance of the previously reported papaya (Carica papaya L.) beta-galactosidase/galactanase (beta-d-galactoside galactohydrolase; EC 3.2.1.23) isoforms, beta-gal I, II and III, as softening enzymes during ripening was evaluated for hydrolysis of pectins while still structurally attached to unripe fruit cell wall, and hemicelluloses that were already solubilized in 4 M alkali. The enzymes were capable of differentially hydrolyzing the cell wall as evidenced by increased pectin solubility, pectin depolymerization, and degradation of the alkali-soluble hemicelluloses (ASH). This enzyme catalyzed in vitro changes to the cell walls reflecting in part the changes that occur in situ during ripening. beta-Galactosidase II was most effective in hydrolyzing pectin, followed by beta-gal III and I. The reverse appeared to be true with respect to the hemicelluloses. Hemicellulose, which was already released from any architectural constraints, seemed to be hydrolyzed more extensively than the pectins. The ability of the beta-galactanases to markedly hydrolyze pectin and hemicellulose suggests that galactans provide a structural cross-linkage between the cell wall components. Collectively, the results support the case for a functional relevance of the papaya enzymes in softening related changes during ripening.     

1-甲基环丙烯采后处理对樱桃番茄果实成熟过程的影响

研究了不同浓度(0、0.035、0.07和0.11μL/L)的乙烯受体竞争性抑制剂1-甲基环丙烯(1-MCP)采后处理对绿熟期樱桃番茄的乙烯合成、果实软化、果实色素(叶绿素、茄红素、β-胡萝卜素)含量消长的影响.0.07 μL/L及其以上浓度的1-MCP降低了前期乙烯合成,同时推迟了乙烯释放高峰,但0.035 μL/L浓度的1-MCP处理并不能抑制内源乙烯合成.1-MCP显著延迟了果实软化和叶绿素降解,但并不影响这两个过程的启动.茄红素合成的启动和积累均受到了1-MCP抑制,而1-MCP并不推迟β-胡萝卜素合成的启动,只抑制其积累.这些结果提示了乙烯调节成熟生理过程的不同机制.对于绿熟期的樱桃番茄,0.07～0.11μL/L的1-MCP是实用的有效处理浓度.1-MCP有效浓度可能用于了解果实的乙烯受体水平和乙烯敏感性.     

Cell wall-degrading enzymes and pectin solubility and depolymerization in immature and ripe watermelon (Citrullus lanatus) fruit in response to exogenous ethylene

Watermelon fruit have been shown to be extremely sensitive to exogenous ethylene, exhibiting acute symptoms of whole-fruit softening and placental-tissue water-soaking following short periods of exposure to the gas. This study addressed the firmness, specific activities of cell wall hydrolases, and solubility and molecular mass properties of polyuronides in placental tissue in response to treatment of intact fruit with ethylene. Watermelon fruit were harvested at the immature and full-ripe stages and exposed to 50 µl l⁻¹ ethylene for 6 days at 20°C. The firmness of placental tissue from ethylene-treated ripe and immature fruit decreased nearly 80% during 6 days of ethylene exposure, whereas the firmness of placental tissue from fruit maintained in air remained relatively constant up to day 3 and then decreased slightly (12%) during the following 3 days of storage. Although ethylene treatment in some cases influenced the levels of extractable placental-tissue polygalacturonase (EC 3.2.1.15), pectinmethylesterase (EC 3.2.1.11), and α -(EC 3.2.1.22) and β -galactosidase (EC 3.2.1.23) specific activities, these effects were not observed for fruit of both developmental stages and appeared not to be directly involved in the water–soaking syndrome. Symptoms of water-soaking were accompanied by increases in the levels of water- and CDTA ( trans -1,2-cyclohexanediamine- N,N,N',N' -tetraacetic acid)-soluble polyuronides and significant molecular mass downshifts in polyuronides in both immature and ripe watermelon fruit. Polyuronide depolymerization in ethylene-treated ripe fruit was extensive. The parallel trends of enzyme changes in ethylene- compared with air-treated fruit indicate that extractable enzyme levels are not associated with development of the water-soaking disorder. The potential involvement of membrane dysfunction in the water-soaking phenomenon is discussed.     

Ethylene is required for both the initiation and progression of softening in pear (Pyrus communis L.) fruit

In order to investigate the physiological role of ethylene in the initiation and subsequent progression of softening, pear fruit were treated with propylene, an analogue of ethylene or 1-methylcyclopropene (1-MCP), a gaseous inhibitor of ethylene action at the preclimacteric or ripening stages. The propylene treatment at the pre-ripe stage stimulated ethylene production and flesh softening while the 1-MCP treatment at the same stage markedly retarded the initiation of the ripening-related events. Moreover, 1-MCP treatment after the initiation of ripening markedly suppressed the subsequent flesh softening and ethylene production. These results clearly indicate that ethylene is not merely a by-product, but plays a crucial role in both the initiation and maintenance of regulating the softening process during ripening. The observations also suggest that ethylene in ripening is regulated entirely in an autocatalytic manner. The mRNA accumulation of pear polygalacturonases (PG) genes, PC-PG1 and PC-PG2, was in parallel with the pattern of fruit softening in both propylene and 1-MCP treatments. However, the expression pattern of pear endo-1,4-beta-D-glucanases (EGase) genes, PC-EG1 and PC-EG2, was not affected in both treatments. The results suggest that ethylene is required for PGs expression even in the late ripening stage, but not for EGases.