Ethylene Antagonist Research Articles

THE ETHYLENE BIOSYNTHESIS IS AFFECTED BY 1-MCP IN CARNATION

1-Methylcyclopropene (1-MCP) is an antagonist of ethylene for receptor binding sites. Carnation (Dianthus caryophyllus L. 'Amelia' and 'Natila') plants were incubated with 1-MCP (500 nl L -1 and 1000 nl L -1 ) for 24h at 20°C. On the other hand, it was found that the cultivars can be stored at 4°C temperature and 70% humidity in a solution of 1% sucrose. The decreases in quality decay and increases in vase life were obtained from the treatments of 1-MCP doses between 'Amelia' and 'Natila' flowers.

FACTORS AFFECTING THE INCIDENCE OF 'RUSSET BROWNING' DISORDER IN 'COX'S ORANGE PIPPIN' APPLES

The ethylene antagonist, 1-methylcyclopropene, is used commercially as SmartFresh SM to retain firmness during shipping and storage of 'Cox's Orange Pippin' apples. However, the application of SmartFresh SM can result in an unsightly darkening of the russeted area in the stem cavity. The symptoms have been termed 'russet browning' disorder. Several studies have been undertaken over the last five seasons. In initial studies, fruit held in bins or cartons were treated with a full or reduced rate of SmartFresh SM to determine the effects of maturity at harvest, time after harvest, SmartFresh SM dose and pack type on the incidence of 'russet browning' after storage. Results indicated that the incidence of 'russet browning' could be reduced by reducing the rate of 1-methylcyclopropene without a significant loss in firmness retention, and that delaying treatment from three days after harvest to seven days after harvest increased the incidence. Pack type, i.e., treating fruit in bins or cartons, had no consistent effect on 'russet browning'. In subsequent studies, the incidence of 'russet browning' was decreased if fruit were treated with a reduced rate of 1-methylcyclopropene after cooling rather than before cooling, and the disorder could be avoided if fruit were treated after cooling and kept cold throughout storage. However, if fruit were given a warming treatment to simulate packing after treatment and short-term storage, the incidence of 'russet browning increased the earlier and longer the fruit were warmed after SmartFresh SM treatment. It is concluded that 'russet browning' disorder can be avoided if fruit are treated with a reduced rate of SmartFresh SM after packing and cooling and then keeping the fruit cold throughout subsequent storage. Avoiding excessive warming in the first two weeks after treatment is likely to be useful in reducing the incidence of 'russet browning', but the disorder could be totally avoided if treated fruit were held at storage temperatures for 6-8 weeks before packing or marketing.

The Copper Transporter RAN1 Is Essential for Biogenesis of Ethylene Receptors in Arabidopsis

Plants utilize ethylene as a hormone to regulate multiple developmental processes and to coordinate responses to biotic and abiotic stress. In Arabidopsis thaliana, a small family of five receptor proteins typified by ETR1 mediates ethylene perception. Our previous work suggested that copper ions likely play a role in ethylene binding. An independent study indicated that the ran1 mutants, which display ethylene-like responses to the ethylene antagonist trans-cyclooctene, have mutations in the RAN1 copper-transporting P-type ATPase, once again linking copper ions to the ethylene-response pathway. The results presented herein indicate that genetically engineered Saccharomyces cerevisiae expressing ETR1 but lacking the RAN1 homolog Ccc2p (Δccc2) lacks ethylene-binding activity. Ethylene-binding activity was restored when copper ions were added to the Δccc2 mutants, showing that it is the delivery of copper that is important. Additionally, transformation of the Δccc2 mutant yeast with RAN1 rescued ethylene-binding activity. Analysis of plants carrying loss-of-function mutations in ran1 showed that they lacked ethylene-binding activity, whereas seedlings carrying weak alleles of ran1 had normal ethylene-binding activity but were hypersensitive to copper-chelating agents. Altogether, the results show an essential role for RAN1 in the biogenesis of the ethylene receptors and copper homeostasis in Arabidopsis seedlings. Furthermore, the results indicate cross-talk between the ethylene-response pathway and copper homeostasis in Arabidopsis seedling development.

Influence of Phytohormones, Culture Conditions and Ethylene Antagonists on Somatic Embryo Maturation and Plant Regeneration in Papaya*

Influence of Phytohormones, Culture Conditions and Ethylene Antagonists on Somatic Embryo Maturation and Plant Regeneration in Papaya*

Arabidopsis RING E3 Ligase XBAT32 Regulates Lateral Root Production through Its Role in Ethylene Biosynthesis

XBAT32, a member of the RING domain-containing ankyrin repeat subfamily of E3 ligases, was previously identified as a positive regulator of lateral root development. Arabidopsis (Arabidopsis thaliana) plants harboring a mutation in XBAT32 produce fewer lateral roots that wild-type plants. We found that xbat32 mutants produce significantly more ethylene than wild-type plants and that inhibition of ethylene biosynthesis or perception significantly increased xbat32 lateral root production. XBAT32 interacts with the ethylene biosynthesis enzymes AMINOCYCLOPROPANE-1-CARBOXYLIC ACID SYNTHASE4 (ACS4) and ACS7 in yeast-two-hybrid assays. XBAT32 is capable of catalyzing the attachment of ubiquitin to both ACS4 and ACS7 in in vitro ubiquitination assays. These results suggest that XBAT32 negatively regulates ethylene biosynthesis by modulating the abundance of ACS proteins. Loss of XBAT32 may promote the stabilization of ACSs and lead to increased ethylene synthesis and suppression of lateral root formation. XBAT32 may also contribute to the broader hormonal cross talk that influences lateral root development. While auxin treatments only partially rescue the lateral root defect of xbat32, they completely restore wild-type levels of xbat32 lateral root production when coupled with ethylene inhibition. Abscisic acid, an antagonist of ethylene synthesis/signaling, was also found to stimulate rather than inhibit xbat32 lateral root formation, and abscisic acid acts synergistically with auxin to promote xbat32 lateral root production.

1-MCP SHORTENS PEONY VASE LIFE

Ethylene action and synthesis inhibitors were evaluated for their effects on cut peony flower longevity and quality. Field-grown 'Karl Rosenfield' and 'Sarah Bernhardt' cut peony flowers were treated for two hours with either 0.5 mM silver thiosulfate (STS) or 0.60 μl L -1 1-methycyclopropene (1-MCP) ethylene action inhibitors, Floralife ® (FLO) at the label recommended dosage, 0.60 μl L -1 ethylene (Eth), or deionized water (CON) before being stored for nine weeks. In addition, cut peony flowers temporarily held for three weeks in refrigerated storage were treated for two hours with either 100 μl L -1 aminoethoxyvinylglycine (AVG), an ethylene synthesis inhibitor or deionized water and monitored for an additional seven week storage period. Vase life, flower weight, bud diameter, degree of petal openness, petal color, rate of ethylene and carbon dioxide (CO 2 ) evolution, and percent disease incidence were monitored. 'Karl Rosenfield' flowers were unaffected by all treatments over the storage time. 'Sarah Bernhardt' flowers responded to STS and 1-MCP treatments during CO 2 evolution, petal color and percent disease incidence measurements. Flowers treated with AVG had slowed reproductive organ development and increased disease incidence. The Floralife ® treatment promoted the longest flower vase life; 1-MCP-treated flowers had the shortest vase life. Flowers treated with STS were lighter and less vivid in color, whereas FLO-treated flowers had darker and more vivid petal color. AVG had little to no effect on flower quality or vase life, with the exception of delayed flower development and increased disease incidence. The decline of vase life and flower quality was significantly related to the length of storage time. The ethylene antagonists used in this study were ineffective at increasing storage longevity and quality of cut peony flowers.

ANTAGONIZING EFFECTS OF (I) VOLATILES, AND (II) WATER SOLUBLE CYCLOPROPENE DERIVATES ON ETHYLENE ACTION

The potency of 12 new volatile cyclopropenes to inhibit ethylene action synthesized at the laboratory of Edward C. Sisler was assessed. The inhibitory effect was evaluated in the following test systems: ethylene-induced ripening of climacteric fruits, ethylene-induced growth modifications in etiolated pea seedlings and abscission of citrus leaf explants. In some of the test systems, the new compounds were found to be more potent ethylene antagonists than 1-MCP, whereas in other systems they were less potent. A novel water soluble inhibitor of ethylene action 3-(cycloprop-1-enylpropanoic acid, sodium salt (CPAS, IL patent application 184729, WO 2009/010981 A1)), was synthesized by D-Pharm, Israel, from one of the new cyclopropene derivatives. CPAS was found to counteract ethylene-induced abscission of citrus leaf explants and of avocado fruit peduncles, to inhibit ethylene-induced leaf epinasty in tomato seedlings, and to prolong the vase-life of carnation and petunia cut flowers. It also considerably delayed fruit ripening processes, such as skin colour change in 'Hass' avocado and banana fruit and softening of peach fruit. Banana and avocado fruit softening were delayed by CPAS to a lesser extent, probably due to insufficient penetration.

Short-term hypoxic hypobaria transiently decreases internal ethylene levels and increases sensitivity of tomato fruit to subsequent 1-methylcyclopropene treatments

Brief treatment of ripening tomato fruit with ethylene transiently negates or reduces sensitivity to subsequent treatments with 1-methylcyclopropene (1-MCP), indicating that internal ethylene levels can modulate responses to 1-MCP. The present study further tested this model by applying 1-MCP to tomato fruit following treatments that transiently decreased internal ethylene concentration (IEC). The hypothesis was that decreases in IEC would result in enhanced sensitivity to the ethylene antagonist. Breaker and pink ‘Florida 47’ tomato fruit were subjected to hypoxic hypobaria (HH) (1.7 kPa O 2, 8 kPa) for 6 h, followed by treatment at ambient pressure with aqueous 1-MCP at a sub-saturating dose (0.93 mmol m −3, 50 μg L −1) and exposure duration (1 min). Immediately following HH, breaker fruit had a 76% lower IEC and enhanced sensitivity to 1-MCP compared with fruit not receiving HH. Increased sensitivity to 1-MCP was evident in further suppression of fruit firmness and hue angle declines, and delayed peak ethylene production. Within 3 h of removal of fruit from HH, IEC had returned to pre-HH values and responses to 1-MCP were comparable with those of fruit receiving 1-MCP without prior HH. Decreased IEC and increased sensitivity to 1-MCP in response to HH were also observed for fruit at more advanced ripening. We addressed whether increased sensitivity to 1-MCP following exposure to HH was a response to reduced pO 2. Breaker and pink fruit were exposed to hypoxic (4.5 kPa O 2) or normoxic (21.3 kPa O 2) hypobaria (21.3 kPa) for 6 h prior to treatment with 0.93 mmol m −3 aqueous 1-MCP. Immediately following HH, IEC was reduced about 61 and 49% in breaker and pink fruit, respectively, accompanied by increased sensitivity to 1-MCP. By contrast, IEC and responsiveness to 1-MCP were unaffected in fruit following exposure to normoxic hypobaria (NH). The results indicate that enhanced sensitivity to 1-MCP following HH is a result of low pO 2-mediated reductions in IEC. The data are consistent with the model that IEC at the time of 1-MCP treatment can modulate response intensity and explain the divergent responsiveness of different climacteric fruits to 1-MCP applied after ripening initiation.

Apyrase (Nucleoside Triphosphate-Diphosphohydrolase) and Extracellular Nucleotides Regulate Cotton Fiber Elongation in Cultured Ovules

Ectoapyrase enzymes remove the terminal phosphate from extracellular nucleoside tri- and diphosphates. In Arabidopsis (Arabidopsis thaliana), two ectoapyrases, AtAPY1 and AtAPY2, have been implicated as key modulators of growth. In fibers of cotton (Gossypium hirsutum), transcript levels for GhAPY1 and GhAPY2, two closely related ectoapyrases that have high sequence similarity to AtAPY1 and AtAPY2, are up-regulated when fibers enter their rapid growth phase. In an ovule culture system, fibers release ATP as they grow, and when their ectoapyrase activity is blocked by the addition of polyclonal anti-apyrase antibodies or by two different small molecule inhibitors, the medium ATP level rises and fiber growth is suppressed. High concentrations of the poorly hydrolyzable nucleotides ATPgammaS and ADPbetaS applied to the medium inhibit fiber growth, and low concentrations of them stimulate growth, but treatment with adenosine 5'-O-thiomonophosphate causes no change in the growth rate. Both the inhibition and stimulation of growth by applied nucleotides can be blocked by an antagonist that blocks purinoceptors in animal cells, and by adenosine. Treatment of cotton ovule cultures with ATPgammaS induces increased levels of ethylene, and two ethylene antagonists, aminovinylglycine and silver nitrate, block both the growth stimulatory and growth inhibitory effects of applied nucleotides. In addition, the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid, lowers the concentration of nucleotide needed to promote fiber growth. These data indicate that ectoapyrases and extracellular nucleotides play a significant role in regulating cotton fiber growth and that ethylene is a likely downstream component of the signaling pathway.

Use of 1-methylcyclopropene for the control of Botrytis cinerea on cut flowers

Cut flowers are marketed for their ornamental characteristics making post-harvest flower life an important determinant of crop value. Botrytis cinerea is one of the most significant post-harvest fungal pathogens causing losses in ornamental plants. Disease caused by this fungus seems to be enhanced by the presence of a ethylene hormone, that both the plant and the fungus are known to synthesize. The aim of the experiment was to determine if 1-methylcyclopropene (1-MCP), an ethylene antagonist, could be used to reduce B. cinerea damage to cut flowers. Six cultivars of four ornamental species: Dianthus caryophyllus ‘Idra di Muraglia’, Rosa × hybrida ‘White Dew’ and ‘Ritz’, Ranunculus asiaticus ‘Saigon’ and ‘Green’, and Cyclamen persicum line ‘Halios Bianco Puro Compatto’ were given three concentrations of 1-MCP (0.38 μl L -1 , 1.14 μL L -1 , and 3.62 μL L -1 ) for 24 hours. Subsequently, 10 petals per cultivar were treated with a B. cinerea conidial suspension (5×103 conidia cm -2 ) and stored in air-tight vases. To evaluate B. cinerea development an arbitrary damage scale (1–7) was used. A high concentration of 1-MCP significantly reduced B. cinerea damage on D. caryophyllus ‘Idra di Muraglia’ and C. persicum ‘Halios White Pure Compact’ petals. In carnation, 1-MCP treatment slowed B. cinerea infection; its threshold level was reached three days after that of the control. In cyclamen, treated petals and control petals remained aesthetically good until day 53 and day 28 respectively. At low concentrations, 1-MCP slowed grey mould on R. × hybrida ‘Ritz’ for up to three days beyond the control. On the two buttercup cultivars ‘Green’ and ‘Saigon’, 1-MCP treatments were not effective. In conclusion, 1-MCP limited pathogen development; its effect depended on the species and the 1-MCP concentration. Further investigations will be performed to improve methods to reduce B. cinerea development on the petals of cut flowers.

Cytokinin and Ethylene Affect Auxin Transport-Dependent Rhizogenesis in Hypocotyls of Common Ice Plant (Mesembryanthemum crystallinum L.)

Hypocotyl explants of Mesembryanthemum crystallinum regenerated roots when cultured vertically with either the apical end (AE) or basal end (BE) in media containing indole-3-acetic acid (IAA). IAA alone induced roots regularly from the basal end of the explants, either from the cut surface immersed in the medium or from the opposite side. The inhibitors of auxin efflux carriers, α-naphthylphthalamic acid (NPA) and 2,3,5-triiodobenzoic acid (TIBA), inhibited rhizogenesis only from AE-cultured explants, indicating the role of polar auxin transport in root regeneration in this system. Cytokinin (zeatin, kinetin, BAP) added to auxin-containing medium reduced rhizogenesis from the explants maintained with BE and AE and additionally changed the IAA-induced pattern of rooting in AE-cultured explants by favoring rooting from the apical end and middle part of the hypocotyl with its concomitant reduction from the basal end. The addition of kinetin did not influence the content of IAA in the explants maintained with AE, suggesting that the cytokinin effect on root patterning was not dependent on auxin biosynthesis. Kinetin, however, strongly enhanced ethylene production. The importance of ethylene in regulating PAT-dependent rhizogenesis was tested by using an ethylene antagonist AgNO3, an inhibitor of ethylene synthesis aminoethoxyvinylglycine (AVG), and a precursor of ethylene, 1-aminocyclopropane-1-carboxylic acid (ACC). AgNO3 applied together with IAA or with IAA and kinetin strongly reduced the production of ethylene, inhibited rhizogenesis, and induced nonregenerative callus from BE, suggesting the need for ethylene signaling to elicit the rhizogenic action of auxin. A reduction of rhizogenesis and decrease of ethylene biosynthesis was also caused by AVG. In addition, AVG at 10 μM reversed the effect of cytokinin on root patterning, resulting in roots emerging only from BE on the medium with IAA and kinetin. Conversely, ACC at 200 μM markedly enhanced the production of ethylene and partly mimicked the effect of cytokinin when applied with IAA alone, thus confirming that in cultured hypocotyls of ice plant, cytokinin affects IAA-induced rhizogenesis through an ethylene-dependent pathway.

Primary Root Growth Regulation: The Role of Auxin and Ethylene Antagonists

We investigated the growth and development of flax roots in the presence of auxin antagonists 4,4,4-trifluoro-3-(indole-3-)-butyric acid (TFIBA), p-chlorophenoxyisobutyric acid (PCIB), and the ethylene inhibitor silver thiosulfate. Of these compounds, silver thiosulfate was most effective in promoting root elongation. All compounds reduced root diameter and root hair development. The effects of TFIBA were reversed by exogenous indole-3-acetic acid (IAA) or 1-aminocyclopropane-1-carboxylic acid (ACC). Because the ethylene and ACC content of roots was reduced by TFIBA and PCIB but increased by silver thiosulfate, we measured the transcription level of five isoforms of ACC synthases (Lu-ACS1-5) and three isoforms of ACC oxidases (Lu-ACO1-3). Lu-ACS1-3 were inhibited by TFIBA and PCIB but promoted by silver thiosulfate and by exogenous IAA. TFIBA inhibited all three ACC oxidase isoforms but PCIB inhibited only Lu-ACO3. Silver thiosulfate and IAA upregulated Lu-ACO1 and Lu-ACO2. Exogenous IAA affected transcription of ACC synthases and ACC oxidases in a concentration-dependent manner. The root promotion by TFIBA and PCIB is related to ethylene, but may also involve auxin interactions.

Ethylene Is Not Involved in Hormone- and Bromoethane-Induced Dormancy Break in Russet Burbank Minitubers

The involvement of ethylene in the dormancy breaking actions of cytokinins, GA, and BE was investigated using Russet Burbank minitubers. Injection of 10 µg tuber−1 BA, CP, GA, NG, or ZEA or 24 hour exposure to BE effectively broke dormancy and stimulated sprout growth over a two-week period. Although ethylene production was slightly enhanced by all treatments, a significant increase in ethylene production was observed in minitubers treated with BE, CP, or NG. Pretreatment with the ethylene antagonists STS or MCP did not affect the dormancy breaking actions of any of the agents tested. Application of the ethylene synthesis inhibitor AVG to NG-treated minitubers, completely suppressed ethylene production but had no effect on dormancy break. Application of exogenous ethylene or stimulation of endogenous ethylene production by ACC treatment did not break minituber dormancy or stimulate sprout growth. Collectively, these results indicate that endogenous ethylene does not play a role in the dormancy breaking actions of cytokinins, GA, or BE.

Cell wall biochemistry of sapodilla (Manilkara zapota) submitted to 1-methylcyclopropene

Sapodilla (Manilkara zapota) is a climacteric fruit that ripens shortly after harvest. Studies on its conservation during storage have been mainly restricted to using low temperatures and modified atmospheres. In this study we investigated the influence of 1-methylcyclopropene (1-MCP) on the physiological and biochemical changes that sapodilla cell wall undergoes during ripening and evaluated its potential to preserve sapodilla fruits at postharvest. Fruits were treated with ethylene antagonist 1-MCP at 300 nL L-1 for 12 h and then stored under a modified atmosphere at 25ºC for 23 d. 1-MCP significantly delayed softening of sapodilla for 11 d as a consequence of inhibition of cell wall degrading enzyme activities, and thus 1-MCP-treated fruit exhibited a less extensive solubilization of polyuronides, hemicellulose and of free neutral sugar when compared to control fruit. Results suggest that delayed softening of sapodilla is largely dependent on ethylene production and perception.

Ethylene regulates lateral root formation and auxin transport in Arabidopsis thaliana

Lateral root branching is a genetically defined and environmentally regulated process. Auxin is required for lateral root formation, and mutants that are altered in auxin synthesis, transport or signaling often have lateral root defects. Crosstalk between auxin and ethylene in root elongation has been demonstrated, but interactions between these hormones in the regulation of Arabidopsis lateral root formation are not well characterized. This study utilized Arabidopsis mutants altered in ethylene signaling and synthesis to explore the role of ethylene in lateral root formation. We find that enhanced ethylene synthesis or signaling, through the eto1-1 and ctr1-1 mutations, or through the application of 1-aminocyclopropane-1-carboxylic acid (ACC), negatively impacts lateral root formation, and is reversible by treatment with the ethylene antagonist, silver nitrate. In contrast, mutations that block ethylene responses, etr1-3 and ein2-5, enhance root formation and render it insensitive to the effect of ACC, even though these mutants have reduced root elongation at high ACC doses. ACC treatments or the eto1-1 mutation significantly enhance radiolabeled indole-3-acetic acid (IAA) transport in both the acropetal and the basipetal directions. ein2-5 and etr1-3 have less acropetal IAA transport, and transport is no longer regulated by ACC. DR5-GUS reporter expression is also altered by ACC treatment, which is consistent with transport differences. The aux1-7 mutant, which has a defect in an IAA influx protein, is insensitive to the ethylene inhibition of root formation. aux1-7 also has ACC-insensitive acropetal and basipetal IAA transport, as well as altered DR5-GUS expression, which is consistent with ethylene altering AUX1-mediated IAA uptake, and thereby blocking lateral root formation.

Ethylene Receptor Antagonists: Strained Alkenes Are Necessary but Not Sufficient

Plants use ethylene as a hormone to control many physiological processes. Ethylene perception involves its binding to an unusual copper-containing, membrane-bound receptor. Inhibitors of ethylene action are valuable to study signaling and may have practical use in horticulture. Past investigation of alkene ligands for this receptor has identified strain as the key factor in antagonism of ethylene binding and action, consistent with known trends in metal-alkene complex stability. However, in this work, this principle could not be extended to other alkenes, prompting development of the proposal that a ring-opening reaction accounts for the unusual potency of cyclopropene ethylene antagonists. Another factor augmenting the affinity of alkenes for the copper binding site is pyramidalization, as in trans-cycloalkenes. The enantiomeric selectivity in the binding of one such alkene to the ethylene receptor demonstrates its protein-composed asymmetric environment.

Ethylene Controls Autophosphorylation of the Histidine Kinase Domain in Ethylene Receptor ETR1

Perception of the phytohormone ethylene is accomplished by a small family of integral membrane receptors. In Arabidopsis, five ethylene receptor proteins are known, including ethylene resistant 1 (ETR1). The hydrophobic amino-terminal domain of these receptors contains the ethylene-binding site while the carboxyl-terminal part consists of a histidine kinase domain and a response regulator domain, which are well known elements found in bacterial two-component signaling. The soluble membrane-extrinsic carboxyl-terminal part of the receptor, which is likely to play an important role in signal transduction, showed intrinsic kinase activity when expressed and purified on its own. However, a correlation between signal input and autokinase activity was not established in these studies, as receptors were missing the transmembrane amino-terminal sensor domain. Thus, it is still unclear whether autophosphorylation occurs in response to perception of the ethylene signal. Here, we report on autophosphorylation studies of purified full-length ETR1. Autokinase activity of the purified receptor is controlled by ethylene or by ethylene agonists like the pi-acceptor compound cyanide. In fact, both signal molecules were able to completely turn off the intrinsic kinase activity. Furthermore, the observed inhibition of autophosphorylation in ETR1 by both molecules could be prevented when the ethylene antagonist 1-methyl-cyclopropene (MCP) was applied.

Enzyme activities and pectin breakdown of sapodilla submitted to 1-methylcyclopropene

The objective of this work was to investigate the influence of 1-methylcyclopropene (1-MCP) at 300 nL L-1 on activities of cell wall hidrolytic enzymes and pectin breakdown changes which Sapodilla (Manilkara zapota cv. Itapirema 31) cell wall undergoes during ripening. Sapodilla were treated with ethylene antagonist 1-MCP at 300 nL L-1 for 12 hours and then, stored under a modified atmosphere at 25º C for 23 days. Firmness, total and soluble pectin and cell wall enzymes were monitored during storage. 1-MCP at 300 nL L-1 for 12 hours delayed significantly softening of sapodilla for 11 days at 25º C. 1-MCP postharvest treatment affected the activities of cell wall degrading enzymes pectinmethylesterase and polygalacturonase and completely suppressed increases in beta-galactosidase for 8 days, resulting in less pectin solubilization. Beta-galactosidase seems relevant to softening of sapodilla and is probably responsible for modification of both pectin and xyloglucan-cellulose microfibril network.

Different responses of goldenberry fruit treated at four maturity stages with the ethylene antagonist 1-methylcyclopropene

Goldenberries ( Physalis peruviana L.) were harvested at four different maturity stages: immature green (IG), mature green (MG), yellow (Y) and orange (OR). Fruit were treated or not with 1-methylcyclopropene (1-MCP) at 25 °C for 20 h and then kept at 20 °C for 8 d. 1-MCP gas concentrations used were 0, 0.5 or 5 μL L −1. Application of 1-MCP delayed the onset of the ethylene climacteric in IG and MG fruit in a dose-dependent fashion, and transiently decreased ethylene production in Y and OR fruit. 1-MCP application transitorily decreased the respiration rate in MG fruit and, to a lesser extent, in IG and Y fruit. In contrast, 1-MCP-treated OR fruit displayed higher respiration rates than control fruit throughout the experimental period. Fruit treated with 5 μL L −1 1-MCP showed for 6 d average CO 2 production levels approximately 41% higher than those of control fruit, with a respiration rate up to 76% higher on day 4. The hue angle was higher in 1-MCP-treated Y goldenberries than in control fruit for 8 d but differences between MG treated and untreated fruit were recorded only at the end of the experiment. In contrast, no differences were detected in IG and OR fruit. 1-MCP-treated fruit were not consistently firmer than untreated fruit during storage. Also, 1-MCP had no effect on soluble solids or ascorbic acid contents. 1-MCP application did not prevent decay in OR fruit but reduced its incidence thus suggesting that it may influence pathogen infection and development in ripe goldenberries.

Softening and Ripening of ‘Athena’ Cantaloupe (Cucumis melo L. var. reticulatus) Fruit at Three Harvest Maturities in Response to the Ethylene Antagonist 1-methylcyclopropene

Three experiments were performed to characterize the physiological responses of an Eastern United States shipper muskmelon (Cucumis melo L. var. reticulatus ‘Athena’) harvested preripe (¼ slip) and during ripening (half-slip, full-slip) to 1 μL·L−1 1-methylcyclopropene (1-MCP), a potent ethylene antagonist effective at significantly extending the time required for climacteric fruit to complete ripening. In the first experiment, preripe fruit were treated with 1-MCP (18 hour, 20 °C) before storage at 15 °C. Softening of preripe ‘Athena’ was significantly suppressed in response to 1-MCP, with firmness of control and 1-MCP–treated fruit declining ≈50% and ≈36% through 12 and 18 days of storage at 15 °C, respectively. By 21 days of storage, firmness of 1-MCP–treated remained near 70 N, minimally within the upper range of whole-fruit firmness values considered acceptable for consumption (50–75 N). Fruit treated with 1-MCP exhibited significantly lower ethylene production, respiratory rates, and electrolyte leakage throughout storage. In a second experiment, muskmelon were treated with 1-MCP (18 hours, 20 °C) at progressively advanced stages of ripening (half- and full-slip stages). Softening was significantly suppressed in half-slip fruit, declining ≈64% and ≈23% in control and 1-MCP–treated fruit, respectively, during 16 days of storage at 15 °C. Advanced-ripening, full-slip fruit were similarly affected, softening ≈60% and ≈25% in control and 1-MCP–treated fruit, respectively, during 10 days at 15 °C. In a third experiment designed to simulate possible commercial handling protocols, full-slip muskmelon were treated with 1-MCP (24 hours, 10 °C) and held at 10 °C for 5 days before transfer to 20 °C. Mesocarp firmness of 1-MCP and control fruit within 2 days of transfer to 20 °C had decreased ≈40% and ≈54%, respectively, compared with values at the start of the experiment. After an additional 2 days at 20 °C, the mesocarp tissue of the respective treatments had softened 42% and 70%. Fruit treated with the ethylene antagonist showed significantly delayed incidence of surface decay and sunken regions compared with control fruit.