Ethylene Exposure Research Articles

Using Ethylene Gas and Chlorpropham Potato Sprout Inhibitors Together

Marketplace preference for lower pesticide residues in foods has led to research to reduce the residue of chlorpropham (isopropyl N-3-chlorophenyl carbamate; CIPC), a postharvest-applied sprout inhibitor which is widely used around the globe to prevent sprouting of stored potatoes (Solanum tuberosum L.). Ethylene gas, an effective, safe and non-toxic sprout inhibitor used in several countries, sometimes has negative effects on the colour of processed potato products when used alone. Trials were conducted over 3 years using cv. Shepody (French fry) and cv. NorValley (potato chips/crisps) to determine whether a combination of these two sprout inhibitors, at reduced dosages, could inhibit sprouting while maintaining good processing colour. CIPC applied at 0, 0.1, 0.25 and 1.0 times the recommended dosage was combined with 4 μll−1 of ethylene gas applied or no ethylene at all (0 ethylene), for 1 day in 4 days, for 1 day in 2 days or continuously, in a factorial design. Sprout inhibition in both cultivars was excellent at all levels of CIPC application except the 0 rate. In both cultivars, sprouting was inhibited by the continuous ethylene treatment. However, all levels of ethylene exposure except the 0 rate negatively affected processing colour in both cultivars. The darkening was dose dependent, whereby the colour was darkest in continuous ethylene and was less affected by the intermittent exposures. In continuous ethylene, the colour was progressively lighter during storage after initial darkening. Shepody tubers appeared to be more sensitive to ethylene than the NorValley tubers. In Shepody only, colour in the ethylene of 1 day in 4 days treatments was progressively darker with increasing time in storage.

Evaluation of ethylene production by ten Mediterranean carnation cultivars and their response to ethylene exposure

Vase life is one of the most important characters of postharvest cut flower quality. The onset of ethylene production and the amount of ethylene produced by flowers vary with the carnation cultivar, and thus influence their vase life. In the present study, differences in ethylene production and the response to exogenous ethylene among carnation cultivars were evaluated. Ten different cultivars: ‘Baltico’, ‘Domingo’, ‘Exotica’, ‘Famosa’, ‘Kiro’, ‘Madame Augier’, ‘Master’, ‘Mundo’, Pilar’ and ‘Reina’were studied. Five flowers for each cultivar were exposed for 8 hours to 1 μL L–1 exogenous ethylene concentration. Ethylene production, fresh weight and water uptake was measured daily throughout theexperiments. The 10 different cultivars studied showed clear differences in vase life, ethylene production, onset timein ethylene production and response to exogenous ethylene. The shortest vase life was for ‘Exotica’ flowers which wasonly 11.6 days, while ‘Baltico’ and ‘Pilar’ lasted 2.5-3 times longer than ‘Exotica’. Most of the investigated cultivarsshowed notable increases in the amount of ethylene. However, ‘Baltico’ and ‘Pilar’ flowers produced only a traceamount of ethylene and had the longest vase life. Results showed that cultivars with a long vase life (‘Baltico’ and‘Pilar’) display high ethylene responsiveness and, in contrast, cultivars with a short vase life (‘Exotica’ and ‘Mundo’) present low responsiveness. The decline in fresh weight of cut flowers observed in the last phase of their vase life occurred earlier in short-lived cultivars than in the longer-lived ones.

Transcriptional regulation of two RTE-like genes of carnation during flower senescence and upon ethylene exposure, wounding treatment and sucrose supply

RTE1 (REVERSION-TO-ETHYLENE SENSITIVITY1) was identified as a positive regulator of ETR1 (ethylene resistant1) function in Arabidopsis; RTEs are a small gene family. Ethylene plays a crucial role in the senescence of carnation (Dianthus caryophyllus L.) flowers. Two cDNA clones encoding putative RTE-like protein (DCRTE1 and DCRTH1) were obtained from total RNA isolated from senescing carnation petals using RT-PCR and RACE techniques. The predicted proteins of DCRTE1 and DCRTH1 consist of 228 and 233 amino acids, respectively. Interestingly, the deduced DCRTE1 protein, like most other RTEs, includes two putative transmembrane domains, while the deduced DCRTH1 protein includes five putative transmembrane domains, according to the TMHMM database. Northern blots showed that the level of DCRTE1 mRNA in petals first decreased then increased remarkably after ethylene production started, and DCRTE1 expression showed an increasing trend in ovaries during natural flower senescence. The amount of DCRTH1 transcripts increased gradually in both petals and ovaries during natural senescence. Exogenous ethylene increased transcript abundance of DCRTE1 and DCRTH1 to various degrees in both petals and ovaries. STS treatment decreased the level of DCRTH1 mRNA in petals and ovaries compared with the control. DCRTE1 and DCRTH1 showed a rapid increase and then a decrease in mRNA accumulation in leaves after wounding. These results suggest that both DCRTE1 and DCRTH1 could play important roles in flower senescence-related signalling. Sucrose treatment did not remarkably affect the amount of DCRTE1 and DCRTH1 mRNAs.

Ethylene Exposure Duration Affects Postharvest Needle Abscission in Balsam Fir (Abies balsamea L.)

Needle loss after harvest is a major problem for Atlantic Canada's Christmas tree and greenery industry. Ethylene is a signal for abscission in balsam fir, but preliminary studies have suggested that the role of ethylene may be influenced by length of exposure. Short-term and long-term ethylene exposure experiments were conducted. Branches were exposed to ethylene for 24 h (short-term) or continuously (long-term) at concentrations of 0 to 1000 ppm. The response variables measured were needle retention duration (NRD), average water use (AWU), and xylem pressure potential (XPP). Short-term exposure to any concentration of ethylene delayed needle abscission by 30 to 40 days. In contrast, long-term exposure to all concentrations of ethylene accelerated abscission, most evident by a 21-day decrease in NRD at 1000 ppm ethylene. There was a 60% decrease in NRD, 160% decrease (more negative) in XPP, and 80% increase in AWU as a result of long-term exposure to ethylene. Overall, our results demonstrate an opposite effect of short-term and long-term ethylene exposure, which suggests that short-term exposure to ethylene might help to precondition balsam fir and delay needle abscission during postharvest handling.

Epitaxial growth and structural property of graphene on Pt(111)

We report on epitaxial growth of graphene on Pt(111) surface. It was found out that the proportion of different rotational domains varies with growth temperature and the graphene quality can be improved by adjusting both the growth temperature and ethylene exposure. Rippled and unrippled domains of high quality graphene are observed. The adhesive energy and electronic structure of two models, representing rippled and unrippled graphene, are obtained with density functional theory calculation, which shows that the interaction between graphene and Pt(111) surface is very weak and the electronic structure is nearly the same as that of a free standing graphene.

Application of exogenous ethylene on postharvest quality of dabai (Canarium odontophyllum Miq.) fruit.

Dabai (Canarium odontophyllum Miq.) is an indigenous fruit to East Malaysia, Palawan (Philippines) and Sumatra (Indonesia). The fruits are hard, and locals prepare the fruit by seeping it in about 50°C water for 15 to 20 min to soften the flesh and eaten with salt and/or sugar. It is hypothesized; and exogenous ethylene could be used as an alternative method to soften the fruit. Therefore, this study was carried out to determine postharvest quality of dabai fruit using 0, 10, 50 and 100 ml/L of exogenous ethylene exposed for 0, 24, 48 and 72 h at 27°C. Carbon dioxide production in ethylene treated dabai fruit followed a pattern, in that as concentration of exogenous ethylene increased, the carbon dioxide production decreased. Exogenous ethylene induced production of endogenous ethylene with highest ethylene production at 24 h exposure among four ethylene exposure duration. The skin and flesh colour of dabai fruit changed as ethylene exposure duration progressed. Exogenous ethylene affected dabai fruit firmness significantly while soluble solids concentration increased as exposure duration advanced. The titratable acidity of dabai fruit increased irrespective of exogenous ethylene concentration and exposure duration. In contrast, pH of dabai fruit decreased as ethylene exposure duration progressed. In short, dabai fruit is sensitive to ethylene at tropical temperature of 27°C.

Factors affecting ethylene sensitivity and 1-MCP response in tulip bulbs

Ethylene has many detrimental effects on tulip quality, including increased bulb gummosis and respiration, reduced rooting, and increased flower bud abortion. In this work, bulbs of four cultivars were exposed to ethylene (10 μL L −1, with or without 1-MCP pretreatment) for different durations or at different times during the fall storage period. An experiment on post-ethylene storage temperature was conducted to test the hypothesis that a period of warm temperature after ethylene exposure is necessary to fully express ethylene injury symptoms that are seen months later after cooling and forcing. The degree of damage (flower abortion) in the sensitive cultivars ‘Apeldoorn’ and ‘World's Favourite’ increased as the duration of ethylene exposure increased to 10 and 16 d, respectively. This effect strongly depended on the timing of ethylene stress, as bulbs given ethylene late in the storage season showed more severe injury than early-treated bulbs. Bulbs that were cooled (9 °C) immediately after ethylene stress had higher flowering percentages than those stored at 17 °C for 2–4 weeks after ethylene stress, demonstrating that a period of warm temperature after ethylene exposure is necessary to allow full expression of the injury. This response was dependent on the cultivar and the timing of ethylene stress. When 1-MCP (1 μL L −1) was applied within 21–28 days prior to the start of ethylene exposure (2 weeks, 10 μL L −1), the ethylene sensitive varieties were protected. Putative ethylene-resistant cultivars ‘Friso’ and ‘Sevilla’ were unaffected by ethylene and showed no response to 1-MCP.

Effects of ethylene on volatile emission and fragrance in cut roses: The relationship between fragrance and vase life

The relationship between fragrance and vase life and the role of ethylene on volatile emission in cut rose flowers was investigated. No relationship was observed between the amounts of volatile compounds emitted and vase life when fragrant and non-fragrant rose cultivars were compared. Neither ethylene production nor respiration rate of flowers was directly related with vase life. Volatile production during vase life was differential and independent among volatiles originating from different biosynthetic groups. Ethylene did not play a role in the regulation of volatile emission in rose flowers. Endogenous ethylene production was very low in most of the cultivars and did not show autocatalytic production trends. Volatile emission patterns during vase life did not parallel endogenous ethylene production. Exogenous ethylene exposure had differential effects among all cultivars, regardless of the fragrance of the flower. Fragrant cultivar ‘Osiana’ was highly sensitive to exogenous ethylene, with petals abscising within 24 h of ethylene (1 μL L −1) exposure while other fragrant cultivars ‘Erin’ and ‘Lovely Dream’ had low ethylene sensitivity. Volatile production was unaffected by exogenous ethylene. The results of this study indicate that volatile emission in cut roses is not regulated by endogenous or exogenous ethylene and occurs independently of petal senescence and/or abscission. These results provide a better understanding of the complexity of volatile emission in rose flowers.

SOME EVIDENCE ABOUT THE PHYSIOLOGICAL BASIS OF FLESH REDDENING SYMPTOMS IN PLUM FRUIT

Flesh reddening has been described as one of the manifestations of chilling injury (CI) symptoms in stone fruits, including plum, peach and nectarine fruit. Flesh reddening in peach and nectarine fruit is most evident around the pit cavity, while symptoms in plum appear initially as discoloration in the fruit flesh periphery that later is extended towards the pit cavity, covering the whole mesocarp. Intriguingly, ethylene has different effects on the incidence of flesh reddening symptoms in these phenotypically related, yet distinct species. While it is exacerbated in plums stored at 5°C under continuous ethylene exposure and is significantly reduced by 1-methylcyclopropene (1-MCP) treatments, in nectarines the opposite is true. This review study indicates that the nature of flesh reddening differs among stone fruits and suggests that in the case of plum ethylene synthesis is not merely an additional consequence of CI symptoms, it is important for the development of the disorder. Finally, the fact that flesh reddening has been observed in non-refrigerated plums during ripening after harvest suggests that flesh reddening in this fruit should be considered a general response to the stresses associated with postharvest storage and not only a CI disorder.

Residual Effects of Ethylene on Tulip Growth and Flowering

Ethylene effects were investigated on two tulip (Tulipa gesneriana L.) cultivars, Markant and Carreria. Pre-cooled bulbs were treated with ethylene (flow-through) for 1 week at 0, 0.1, 1.0, or 10 μL·L−1 (± 10%) in a modified hydroponic system. After ethylene exposure, plants were either destructively harvested for root measurements or forced in a greenhouse for flower measurements. Ethylene exposure at concentrations as low as 1 μL·L−1 during the first week of growth reduced shoot and root elongation and subsequently increased flower bud abortion. At 10 μL·L−1, root growth was essentially eliminated. In a second experiment, bulbs were treated overnight with 1-methylcyclopropene (1-MCP) before a 7-day exposure to 1 μL·L−1 ethylene. 1-MCP pretreatment eliminated the harmful effects of ethylene on root and shoot growth. This study illustrates the effects of ethylene exposure during hydroponic tulip production and demonstrates a potential benefit to treating bulbs with 1-MCP before planting.

A kinetic analysis of hyponastic growth and petiole elongation upon ethylene exposure in Rumex palustris.

Complete submergence is an important stress factor for many terrestrial plants, and a limited number of species have evolved mechanisms to deal with these conditions. Rumex palustris is one such species and manages to outgrow the water, and thus restore contact with the atmosphere, through upward leaf growth (hyponasty) followed by strongly enhanced petiole elongation. These responses are initiated by the gaseous plant hormone ethylene, which accumulates inside plants due to physical entrapment. This study aimed to investigate the kinetics of ethylene-induced leaf hyponasty and petiole elongation. Leaf hyponasty and petiole elongation was studied using a computerized digital camera set-up followed by image analyses. Linear variable displacement transducers were used for fine resolution monitoring and measurement of petiole growth rates. We show that submergence-induced hyponastic growth and petiole elongation in R. palustris can be mimicked by exposing plants to ethylene. The petiole elongation response to ethylene is shown to depend on the initial angle of the petiole. When petiole angles were artificially kept at 0 degrees, rather than the natural angle of 35 degrees, ethylene could not induce enhanced petiole elongation. This is very similar to submergence studies and confirms the idea that there are endogenous, angle-dependent signals that influence the petiole elongation response to ethylene. Our data suggest that submergence and ethylene-induced hyponastic growth and enhanced petiole elongation responses in R. palustris are largely similar. However, there are some differences that may relate to the complexity of the submergence treatment as compared with an ethylene treatment.

Genotypic Variation in the Postharvest Performance and Ethylene Sensitivity of Cut Rose Flowers

Natural variation in the postharvest quality and longevity of ornamental plants can often be related to differences in their response to ethylene. In the present study, we determined the postharvest performance and ethylene sensitivity of cut flowers from 38 cultivated Hybrid Tea rose genotypes. The vase life of the cultivars varied considerably from 4.5 to 18.8 days at 21 °C. There was also substantial variation in the degree of flower opening among genotypes. Exposure to 1 μL·L−1 ethylene for 24 h at 21 °C reduced the longevity of 27 cultivars by 0.8 to 8.4 days (18% to 47%) by accelerating petal wilting and abscission. Ethylene treatment also significantly reduced rates of flower opening in 17 sensitive cultivars and in six cultivars that showed no ethylene-related reduction in vase life. Five cultivars showed no reduction in vase life or flower opening in response to ethylene exposure. Pre-treating stems with 0.2 mm silver thiosulfate liquid or 0.9 μL·L−1 1-methylcyclopropene (1-MCP) gas for 16 h at 2 °C reduced the deleterious effects of ethylene. The release of 1-MCP from two sachets containing EthylBloc™ into individual shipping boxes also protected flowers against ethylene applied immediately after a 6-d commercial shipment. The duration of protection afforded by the 1-MCP sachet treatment was greatest when flowers were maintained at low temperature.

Response of ‘Fuyu’ persimmons to ethylene exposure before and during storage

In the export of ‘Fuyu’ persimmon, fruit are airfreighted at ambient temperatures, or seafreighted at low temperatures using modified atmosphere (MA) packaging. Since persimmons are climacteric and ethylene sensitive, exposure to exogenous ethylene may accelerate natural softening at ambient temperature (e.g. airfreight) as well as aggravate chilling injury during coolstorage (e.g. seafreight). In the present work, the response of this cultivar to exogenous ethylene exposure was studied in four critical handling scenarios that might occur in a commercial chain. Non-packed fruit exposed to ethylene and then held at 20 °C (simulated airfreight) showed the greatest sensitivity to ethylene; fruit firmness and colour during shelf life were affected by even 1 d of exposure to 0.2 μL L −1 ethylene. Lower sensitivity was observed when fruit were stored at 0 °C under MA conditions after ethylene exposure at 20 °C (simulated pre-packing exposure-seafreight), where fruit quality was not affected by exposures of 1 d at ≤1 μL L −1, and only slightly by 2 d at <0.5 μL L −1. When ethylene exposure was carried out at 0 °C after sealing fruit in MA bags (simulated post-packing exposure-seafreight), fruit showed the lowest sensitivity to ethylene, with only slight decrease of firmness with ethylene exposure at the end of the storage period, and no significant effect on exposure at the beginning of the storage period. Influence of the temperature of storage, temperature of exposure to ethylene, use of MA and timing of exposure during coolstorage in the response of the fruit to exogenous ethylene are discussed.

Effect of nitric oxide on the sensitivity of banana fruit slices to ethylene

SummaryThe effects of nitric oxide (NO) treatment on the sensitivity of banana fruit slices to ethylene were investigated. Fruit slices were partial-pressure infiltrated for 3 min in a NO donor solution of 5 mM sodium nitroprusside (SNP), followedby treatment with 100 µl l1 ethylene for 24 h, then packed into polyethylene bags and stored for 5 d at 24°C. Control slices were treated with distilled water instead of SNP, then treated with ethylene. Changes in fruit firmness, chlorophyll content, respiration rate, the activities of three cell wall modifying enzymes [polygalacturonase (PG), endo-ß&-1,4-glucanase (EGase), and ß-galactosidase (ß-Gal)], and total amylase activity were measured. Expression of the expansin (MaExp1) and ethylene receptor (MaERS2) genes were also analysed. The application of NO, prior to ethylene exposure, retarded pulp softening and peel de-greening. Pre-treatment with NO also decreased the respiration rate of banana fruit slices during ripening. Delayed pulp softening by NO was associated with decreased activities of PG, EGase, ß-Gal, and total amylase, as well as reduced expression of the MaExp1 gene. Expression of the MaERS2 gene was also suppressed in NO-treated banana fruit slices. Collectively, these findings suggest that NO pre-treatment decreased the sensitivity of banana fruit slices to ethylene, and thereby delayed ripening.

Gene expression of pathogenesis-related protein during banana ripening and after treatment with 1-MCP

Pathogenesis-related (PR) proteins are generally considered as plant defense proteins associated with preventing or limiting pathogen and insect attack. Identification and characterization of a fruit PR1, the MaPR1a gene, is reported here for the first time from banana. The MaPR1a cDNA is 606 bp long and contains an open reading frame of 489 nucleotides encoding 162 amino acid residues. The deduced amino acid sequence of MaPR1a has a high level of identity with PR1 proteins from other plants. Southern blot as well as nucleotide sequence analyses using the Global Musa Genomics Consortium database suggests that MaPR1a is encoded by a multigene family in banana. Ethylene exposure of unripe mature banana fruit induced MaPR1a expression, which increased with ripening, and 1-methylcyclopropene (1-MCP) treatment prior to ethylene exposure inhibited expression. No expression was detected in any other tissue which suggests that MaPR1a gene family members are fruit-specific and ripening related. The 1506 bp proximal promoter of the gene shows the presence of cis-acting elements which could bind to sets of transcription factors as well as regulate jasmonic acid (JA) and salicylic acid (SA) signalling. Our expression analysis suggests that in addition to ethylene, JA and SA also induce expression of MaPR1a in fruit tissue.

Ethylene exposure is not harmful to &lt;i&gt;Ranunculus asiaticus&lt;/i&gt; tuberous roots

We investigated the influence of ethylene exposure on dry or hydrated tuberous roots of the ornamental geophyte Ranunculus asiaticus. Ethylene concentrations up to 10 μL·L-1 for 3 weeks in the dry state or at least 1 week in the hydrated state had negligible influence on post-planting growth in any of the observed parameters. We therefore conclude that Ranunculus asiaticus tuberous roots are ethylene-insensitive and special precautions to avoid ethylene exposure are unnecessary.

Petunia floral volatile benzenoid/phenylpropanoid genes are regulated in a similar manner

Petunia (Petunia x hybrida cv 'Mitchell Diploid' [MD]) flowers emit high levels of multiple floral volatile benzenoid/phenylpropanoid (FVBP) compounds from anthesis to senescence in a concerted manner. Here we show seven genes responsible for the production of emitted FVBPs share similar transcript accumulation profiles through an analysis of four expression criteria. As a group, the FVBP gene transcripts accumulate to high levels in petal limb tissue of MD flowers from anthesis to senescence. Two to four hours of exogenous ethylene exposure reduces transcript levels of all FVBP genes examined, but 2h of treatment will not accelerate senescence or reduce volatile emissions in MD flowers. The FVBP genes show two obvious rhythmic patterns of transcript accumulation; however, corresponding enzyme activities of a subset of FVBP gene products do not. Together, these results depict floral volatile benzenoid/phenylpropanoid biosynthesis as a specific system with multiple regulatory features. One such feature is the highly regulated transcript accumulation of the FVBP genes. Additionally, ethylene may have a regulatory role in the FVBP system prior to a floral senescence program.

Subcellular Localization and Changes in mRNA Abundance of CEBP, a Nuclear-Encoded Chloroplast Protein, During Flower Development and Senescence

CEBP, a nuclear-encoded chloroplast protein, has been previously cloned as a putative transcription factor involved in ethylene signaling in carnation development and senescence. In order to more clearly define CEBP role and function, we carried out experiments to define its pattern of mRNA abundance and possible subcellular localization. Changes in CEBP mRNA abundance showed a dramatic drop from anthesis to open flower stage of development immediately preceding the ethylene climacteric associated with flower senescence. A similar but less dramatic decrease in CEBP was observed upon ethylene exposure, again before endogenous climacteric ethylene was observed. The pattern of CEBP mRNA abundance suggests a response to or involvement in the initial steps of the petal senescence process. GFP co-localization showed that a GFP–CEBP construct was directed to the nucleus, whereas a CEBP–GFP construct localized to the chloroplast. Nuclear localization was expected as CEBP was cloned as an ethylene-responsive element-binding protein or transcription factor. The role and function of CEBP in the chloroplast, however, remains unclear. Future lines of inquiry based on our results are discussed.

Influence of the Natural Ripening Stage, Cold Storage, and Ethylene Treatment on the Protein and IgE-Binding Profiles of Green and Gold Kiwi Fruit Extracts

Kiwi fruit is an important source of food allergens, the number and relevance of which are still the object of investigation. Following a comparative analysis of the protein profiles in SDS-PAGE and IgE immunoblotting, a significant influence of conditions such as the ripening stage and the extraction method on the composition of green and gold kiwi fruit extracts was observed. Furthermore, the experimental data indicate that, mostly in the green species, a ripe fruit may have a different concentration of total proteins and a different amount of single components when ripeness is reached by different means of postharvest handling, such as ethylene exposure with or without previous cold storage. In summary, this study emphasizes the level of complexity associated with the preparation of extracts when a known and defined concentration of proteins/allergens is requested.

Effect of ethylene treatment on expression of polyuronide-modifying genes and solubilization of polyuronides during ripening in two peach cultivars having different softening characteristics

We focused on modification of polyuronides during ripening to clarify the mechanisms involved in peach fruit softening and textural changes. Fruit of the stony hard type peach ‘Miharu Hakuto’ softened during ripening in ethylene-free air, but did so more slowly than the melting type peach ‘Kawanakajima Hakuto’. In addition, the stony hard type peach in ethylene-free air did not develop a melting texture, and solubilization of polyuronides did not occur during ripening, although the fruit gradually softened. Exposure of the stony hard type peach to continuous ethylene promoted fruit softening and development of a melting texture and induced the solubilization of polyuronides to the same levels as in the melting type peach. Expression of the polygalacturonase gene PpPG2 was higher than that of PpPG1 and PpPG3, during ripening in both cultivars. PpPG2-mRNA in the melting type peach showed a slight accumulation at harvest and markedly increased during ripening at 20 °C. Expression of PpPG2 in the stony hard type peach in ethylene-free air was considerably lower than that in the melting type peach, and ethylene exposure of the stony hard type peach up-regulated the mRNA level of PpPG2 to that of the melting type peach. The mRNAs of two pectin methylesterase genes, PpPME1 and PpPME2, in stony hard type peach in ethylene-free air were reduced during ripening at 20 °C as compared with these genes in the melting type peach. Continuous ethylene exposure up-regulated PpPME2 mRNA in the stony hard type peach. The mRNAs of two pectate lyase genes, PpPL1 and PpPL2, were expressed constitutively throughout ripening in both cultivars. These results show that ethylene plays an important role in the solubilization of polyuronides and development of a melting texture in peach fruit. In addition, PpPG2 and PpPME2 might be involved in the solubilization of polyuronides in peach fruit.