Internal Ethylene Levels Research Articles

Emission Patterns of Esters and Their Precursors Throughout Ripening and Senescence in ‘Redchief Delicious’ Apple Fruit and Implications Regarding Biosynthesis and Aroma Perception

The volatile profile of ‘Redchief Delicious’ apple (Malus ×domestica Borkh.) fruit was evaluated at 18 time points from 3 weeks before to 8 weeks after onset of autocatalytic ethylene production to capture the dynamics associated with development from mature green to senescent fruit. Minor amounts of ester production began several days before the onset of ethylene production. Ester production rose rapidly as internal ethylene levels increased beyond 22 nmol·L−1 (0.5 µL·L−1). Peak ester production roughly coincided with maximum ethylene synthesis, declining thereafter. Ester production was further evaluated according to the acid- (alkanoate) and alcohol- (alkyl) derived portions of the ester. The maximum rate of production for a given ester tended to occur later in development as the chain length of the alcohol-derived portion declined. The production rate for many esters paralleled the rate of emanation of their respective alcohol substrates, suggesting that availability of the alcohols limits ester production more than availability of the acid substrates. Combining production rates with sensory descriptors and human sensitivity to individual volatiles permitted approximations of aroma sensations likely engendered by the fruit throughout ripening. Overripe and alcoholic sensations are predicted to increase 2 weeks after the initiation of ripening in response to an increase in the production of ethyl esters. Acetate esters predominated, comprising 50% to 80% of esters throughout maturation and ripening, indicating that the substrate acetyl-CoA may be at saturating levels for alcohol acyl transferase (AAT) at the final step of ester formation. Acetate feeding did not enhance ester production, although label from 13C-acetate was extensively incorporated into esters. The data are consistent with the action of multiple AAT isozymes differing in activity and substrate preference. Incorporation of labeled 13C-acetate into precursors of esters, alcohols, and acids, reflected ester biosynthesis via 1- and 2-carbon chain elongation pathways in ripening ‘Redchief Delicious’ apple fruit.

Dry matter content association with time of on-tree maturation, quality at harvest, and changes in quality after controlled atmosphere storage for ‘Royal Gala’ apples

On-tree maturation was monitored in a commercial ‘Royal Gala’ apple orchard in two separate years (2016 and 2017) and was found to advance more quickly in 2017 as compared with 2016. Dry matter was predicted using a handheld infrared spectrometer and dry matter content (relative to fresh weight) was 18.2% in 2016 and 14.7% in 2017. The lower average dry matter content in 2017 was hypothesized to be associated with accelerated maturation on the tree. Apples were harvested for storage testing, in both years, at a target maturity at which internal ethylene levels had reached approximately 1 μL·L−1, starch clearing index was between 2 and 4 on the Cornell starch chart, and IAD value (measure of relative chlorophyll content in the peel) was approximately 0.5. Consequent, instrumentally measured flesh quality changes were monitored after ultra-low oxygen, controlled atmosphere (CA) storage (0.7 kPa O2 + 1.0 kPa CO2) at 0.5 °C for 3 and 6 mo. The firmness, soluble solids, and titratable acidity were much higher in the apples from the 2016 harvest. While these quality measures declined during 3 and 6 mo of storage, they were consistently higher in the apples from the 2016 season. These results show that when dry matter contents were higher for ‘Royal Gala’ apples from this orchard, harvest maturity was delayed and fruit were much firmer and had higher contents of soluble solids and somewhat higher titratable acidity at harvest and after ultra-low oxygen CA storage for up to 6 mo.

Relationship of IAD index to internal quality attributes of apples treated with 1-methylcyclopropene and stored in air or controlled atmospheres

The research was conducted to evaluate the relationship between IAD index (index of absorption difference between 670 and 720nm) values and internal quality attributes of apples treated with 1-methylcyclopropene (1-MCP) and stored in air and controlled atmospheres (CA). Apples of ‘8S6923’ (Aurora Golden Gala™), ‘Fuji’ and ‘Royal Gala’ were tested. The results with Aurora Golden Gala™ show that IAD index values were maintained at higher levels if the fruit were stored in CA and that 1-MCP had no significant effect on retaining at-harvest values. The IAD values correlated with chlorophyll a content in the peel (R2=0.95, P<0.0001), but not with chlorophyll b content, internal ethylene levels, firmness or titratable acidity. ‘Royal Gala’ apples showed a similar response to Aurora Golden Gala™ apples, showing no correlation between IAD index values and internal quality attributes of those apples when treated with 1-MCP and/or CA. In contrast, ‘Fuji’ apples showed a relationship between IAD index value changes and internal ethylene concentrations (R2=0.67, P<0.05) and titratable acidity changes (R2=0.89, P<0.01), but not firmness. These results suggest that when 1-MCP and/or CA are applied to apples after harvest, that IAD index values do not consistently correlate to any internal quality attributes other than peel chlorophyll a content.

FACTORS INFLUENCING THE EFFICACY OF COMMERCIALLY APPLIED 1-METHYLCYCLOPROPENE (1-MCP)

1-MCP, an inhibitor of ethylene perception, is applied commercially to deciduous crops to extend storage duration and improve shelf-life quality. The importance of harvest maturity and delays in commercial 1-MCP applications after harvest can be observed in fruit quality following cold storage and shelf life. Pack houses are continually looking to improve treatment efficacy and to develop knowledge of the benefits that they can expect after storage from this technology. This study was initiated to improve 1-MCP application guidelines. 'Golden Delicious' and 'Granny Smith' apples were harvested weekly from the beginning of the optimum picking window, until fruit were of a post optimum maturity. Fruit subjected to 625 μl/L 1-MCP, 1, 4, 7 and 14 days after harvest were cold stored with untreated fruit for 16 weeks at -0.5°C, followed by a shelf life of 7 days at 20°C. Immediately after each 1-MCP application, treated fruit were subjected to a 7 day ripening period at 20°C to determine the efficacy of the application. The importance of applying 1-MCP to 'Golden Delicious' apples as soon as possible after harvest was confirmed, and indicated storage and shelf life benefits when fruit are treated within 7 days of harvest. 1-MCP applied 14 days after harvest did not show any storage or shelf life benefits. Fruit not treated with 1-MCP were all below the UK supermarket grade of 56.9 N (5.8 kg force) after 16 weeks cold storage, regardless of harvest maturity. All fruit, treated with 1-MCP within 7 days of harvest, made the UK supermarket grade. 1-MCP applied to 'Granny Smith' apples up to 14 days after harvest maintained flesh firmness irrespective of harvest maturity, with all fruit making the supermarket grade of 66.7 N (6.8 kg force) after cold storage. However, superficial scald control was reduced when 1-MCP was applied more than 7 days after harvest. 1-MCP treated 'Granny Smith' apples did not soften during shelf life periods. Internal ethylene levels of 1-MCP treated fruit were an accurate indicator of treatment efficacy, storage potential, and the physiological ripening responses of 'Golden Delicious' and 'Granny Smith' apples following storage and shelf life. The significance of these findings is discussed, in terms of practical guidelines to 1-MCP application to 'Golden Delicious' and 'Granny Smith' apples.

Quality and volatile attributes of attached and detached ‘Pluk Mai Lie’ papaya during fruit ripening

The ‘Pluk Mai Lie’ papaya ( Carica papaya L.) is a promising cultivated fruit for use in fresh and processed products due to its firm flesh, but the aroma it releases is flat. Changes in quality and volatile profiles were analyzed during on- and off-tree fruit ripening. Detached fruit ripened faster than attached fruit, accumulating high internal ethylene levels. Aside from peel color, which was redder in on-tree ripened fruit, most quality attributes changed similarly in the two ripening situations. A slight increase in total soluble solids (TSS) was measured from the onset of the preclimacteric stage, whereas titratable acidity (TA) remained stable throughout the development. Whereas 2-ethyl-1-hexanol was found specifically in green fruit, ethyl octanoate emerged only in fully-ripe fruit. Furthermore, benzyl isothiocyanate was the most abundant volatile and was present in fruit at every stage except full ripening. The production of total esters, highly correlated with a loss of firmness and an increase in cavity ethylene accumulation, was about 10-fold higher in off-tree ripened fruit. The levels of methanol and ethanol sources in fruit increased steadily throughout ripening, with esters formed from ethyl alcohol predominating from the half-ripe through the senescence phases. The alcohol dehydrogenase activity in the mesocarp increased dramatically during the early ripening stages, whereas alcohol acetyltransferase was active throughout ripening. No difference in volatile profiles was found in the papaya fruit during on-tree and postharvest ripening.

EFFECT OF CONTROLLED ATMOSPHERE STORAGE ON INTERNAL ETHYLENE, ALPHA-FARNESENE, TOTAL ESTERS, AND TOTAL PHENOLIC CONCENTRATIONS OF APPLES

Three varieties of apples were harvested from a research orchard and stored in cold storage (CS), controlled atmosphere (CA), and low-oxygen (LO) CA conditions. 'McIntosh' apples showed scald in November if stored at 20°C, and in March if stored in CS and CA storage at 3°C. 'Empire' apples showed no scald during storage. 'Delicious' apples showed scald in March if stored in CS at 0°C. Higher internal ethylene levels were found in January than during earlier or later months of the storage period. CA and LO storage reduced the magnitude of high ethylene in January. When sampled from the same storage conditions, apples sampled in March had higher total esters and Alpha-farnesene than apples sampled in November. When sampled in March, the LO stored apples had lower total esters than the CS and CA stored apples. In general, there was a positive linear relationship between the total esters and alpha-farnesene concentrations in apples. Apple peel had almost double the amount of total phenolic concentrations compared to apple flesh. 'Empire' apples had less than half of the total phenolic concentrations in both the flesh and the peel than 'McIntosh' and 'Delicious' apples.

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.

Delay of tomato fruit ripening in response to 1-methylcyclopropene is influenced by internal ethylene levels

Using tomato fruit as a model system, this study tested the idea that internal ethylene levels can modulate the efficacy of 1-MCP at suppressing ripening in climacteric fruits. In the first experiment, breaker-turning stage tomato (cv. Sebring) fruit were treated with gaseous 1-MCP (SmartFresh SM Quality System) under conditions (21.7 μmol m −3, 516 nL L −1) affording maximum inhibition of ripening, followed by subsequent exposure to 4.07 mmol m −3 (100 μL L −1) ethylene for 3 or 6 h. Fruit softening and hue angle decline in 1-MCP-treated fruit were minimally affected in response to ethylene, consistent with strong binding of 1-MCP for ethylene receptors. In contrast to sequential 1-MCP and ethylene treatments, simultaneous treatment of breaker-turning ‘Sebring’ tomato fruit with 100 μL L −1 ethylene and gaseous 1-MCP completely negated the capacity of 1-MCP to inhibit fruit softening and hue angle decline. When breaker-turning fruit were treated with 100 μL L −1 ethylene for 6 h followed by exposure to aqueous 1-MCP (3.70 mmol m −3, 200 μg L −1) at levels eliciting maximum inhibition of tomato ripening, sensitivity to 1-MCP was significantly reduced in the short-term (0–1 h) and recovered within 6 h to patterns characteristic of fruit receiving 3.70 mmol m −3 aqueous 1-MCP without prior exposure to ethylene. Re-sensitization was reflected in patterns of softening, climacteric ethylene and respiratory responses, hue angle decline, lycopene content and titratable acidity changes. The time required for re-sensitization to 1-MCP paralleled the time required for return of internal ethylene levels to concentrations present prior to ethylene treatment. We propose that internal ethylene levels may contribute to the divergent sensitivities of some climacteric fruits to 1-MCP applied after initiation of ripening.

1-MCP (SMARTFRESH™) CONTROLS SUPERFICIAL SCALD DEVELOPMENT AND MAINTAINS APPLE QUALITY DURING LONG TERM STORAGE

Superficial scald (scald) is one of the major physiological disorders that occur during long term cold storage of apples. Scald is currently controlled by the postharvest application of diphenylamine (DPA), however there is a growing need to seek alternative control methods. A promising reliable alternative to DPA is 1-methylcyclopropene (1-MCP, SmartFresh ). The aim of this storage project was to assess 1-MCP (SmartFresh ) on apple quality and superficial scald development during storage. Preclimacteric 'Granny Smith' and climacteric 'Red Delicious' apples were treated with SmartFresh , DPA (current approved rate) or left untreated (control) before storage at 0°C in either air or controlled atmosphere (CA, 2% O 2 and 1% CO 2 ). SmartFresh was applied in an air tight container as soon as possible after harvest. The results showed that both the commercial DPA and SmartFresh treatments controlled superficial scald equally well in both 'Red Delicious' and 'Granny Smith' apples stored in air and CA for up to eight and ten months, respectively. CA storage maintained the quality of untreated and SmartFresh treated fruit. However even under CA storage, some quality benefits such as retention of firmness in 'Red Delicious' apples were observed in SmartFresh treated fruit during storage and after storage compared to untreated control or DPA treated fruit. The prestorage SmartFresh treatment also significantly reduced the levels of internal ethylene in both apple varieties in air and CA stored fruit and at all removal times for up to ten months storage. The lowering of ethylene production and action in the treated fruit reduced or lowered subsequent physiological effects during storage. This was evident in the retention of flesh firmness and green background colour in SmartFresh treated fruit.

FRUIT QUALITY AND STORABILITY OF 'ELISE' APPLES DEPENDING ON THE ROOTSTOCK

The effect of fifteen rootstocks (P 2, P 14, P 16, P 22, Nr 47, P 59, P 60, B 9, B 146, B 396, PB-4, M.9 EMLA, M.26, M.27 and M.7) on the storability of 'Elise' apples was studied in the 1999-2001 seasons. Measurements during harvest included mean fruit weight, flesh firmness, starch index, soluble solids and internal ethylene. After six months of cold storage, weight loss, firmness, soluble solids and incidence of storage diseases and disorders were determined. Trends showing higher firmness values for fruits from trees on red-leaved rootstocks (B 9, P 60, B 396, P 59) were noted. Fruits from trees on P 2 resulted in higher than average internal ethylene levels, although values obtained for M.27 were lower than average. B 9, P 59 and M.27 resulted in higher values of the Streif index that corresponded with later ripening. The smallest fruits were noted for super dwarfing rootstocks PB-4, P 22 M.27 and P 59, while the biggest were on P 14, M.7 and P 2. A low percentage of physiological disorders of fruits was noted for B 9, B 396, P 59 and Nr 47. A high seasonal variation was observed for firmness, climacteric ethylene production, maturity indices and fruit quality after storage.

Aminoethoxyvinylglycine Effects on Late-Season Apple Fruit Maturation

Aminoethoxyvinylglycine (AVG) inhibits 1-aminocyclopropane-1-carboxylic acid (ACC) synthase, and thus blocks ethylene synthesis. Preharvest foliar application of AVG to apple (Malus domestica Borkh.) fruit retards several key events of maturation including climacteric ethylene production, starch conversion to sugars, fruit softening, and abscission zone development. Although the impact of AVG on apple fruit maturation is well known, the biochemical basis of these effects is not well understood. The effects of AVG application on Redchief ‘Delicious’ apple fruit maturation were studied. AVG applied four weeks prior to harvest significantly reduced internal ethylene levels, amylose degradation, and accumulation of sucrose, glucose, and sorbitol. Because AVG application coincidentally inhibited starch degradation and the increase in internal ethylene, we investigated the enzymatic basis of starch mobilization in apple fruit. Amylase activity was somewhat reduced in AVG-treated fruit. Amylase activity was less in AVG-treated fruit during the early stages of starch mobilization. Starch phosphorylase activity increased dramatically during the later stages of starch mobilization, but was not affected by AVG treatment. Soluble starch synthase activity was also unaffected by AVG treatment and remained constant throughout the eight-week harvest period. Moreover, AVG did not affect the levels of amylopectin, fructose, malate, ascorbate, citrate, or anthocyanin. These results suggest that apple fruit ripening has both ethylene-dependent and -independent processes occurring simultaneously.

Induction of chill-induced ripening in Fuji apples is a function of both temperature and time

Ethylene production is stimulated by chilling in some cultivars of apples, citrus, cucumbers and pears. The apple varieties Granny Smith, Lady Williams and Fuji can be induced to ripen by a period of chilling at 0°C in air, which hastens the onset of the rise in ethylene production.Fuji apples were susceptible to rapid ripening if stored in air at low temperatures (&lt;10°C). The induction of rapid ripening occurred in both early and late harvested fruit and was correlated with increased activity of 1-aminocyclopropane-1-carboxylic acid oxidase during low temperature storage. The induction of rapid ripening caused the fruit to soften more quickly after cold storage than after continuous exposure to 20°C. Rapid ripening could be prevented by storing fruit in controlled atmosphere (CA) storage (2%�O2 and &lt;1% CO2). Fruit had lower internal ethylene levels following CA storage than following low temperature air storage. The practical solution for growers would therefore be to store Fuji apples in CA, even for short periods, to optimise fruit quality for the consumer.

Enhanced growth and ethylene increases spiral grain formation in Picea abies and Abies balsamea trees

Spiral grain angle in Norway spruce (Picea abies) trees and balsam fir (Abies balsamea) seedlings was investigated in relation to growth rate, endogenous and applied ethylene. Trees from stands of Norway spruce, which were irrigated and fertilised in order to enhance growth, and trees having different growth rates in non-treated stands were studied. Stem growth rate at the stand level (m3 ha–1 year–1) was measured annually, or by means of microscopy on stem sections as the number and size of tracheids produced. Enhanced growth increased ethylene evolution and maintained a high level of left-handed spiral grain angle in comparison to slower-growing trees. An increased number of earlywood tracheids in fast growing trees was correlated to a more left-handed spiral grain angle. Ethrel, applied to stems of balsam fir seedlings, increased the internal ethylene levels in parallel with increased left-handed spiral grain angle. The results indicate that ethylene regulates the extent of spiral grain angle.

Physicochemical properties and application of pullulan edible films and coatings in fruit preservation

AbstractThe effects of water, sorbitol and a sucrose fatty acid ester (SE) on the water sorption behaviour and thermal and mechanical properties of pullulan‐based edible films as well as the physiological responses of fruit coated with pullulan have been studied. Incorporation of sorbitol or SE in pullulan films resulted in lower equilibrium moisture contents at low to intermediate water activities (aw), but much higher moisture contents at aw &gt; 0.75; estimates of monolayer values (within 4.1–5.9 gH2O kg−1 solids) were given by application of the Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–DeBoer (GAB) models. A single glass–rubber transition (Tg), attributed to the polysaccharide component, was detected by calorimetry and dynamic mechanical thermal analysis (DMTA) at a sorbitol level of 15–30% DM. With both tests the strong plasticising action of water and polyol was evident in the thermal curves, and the Tg vs moisture content data were successfully fitted to the Gordon–Taylor empirical model. Multifrequency DMTA measurements provided estimates for the apparent activation energy of the glass transition in the range of ˜ 300–488 kJ mol−1. With large‐deformation mechanical testing, large decreases in Young's moduli (tensile and three‐point bend tests) were observed as a result of water‐ and/or polyol‐mediated glass‐to‐rubber transition of the polymeric films. In the moisture content range of 2–8%, increases in flexural modulus (E) and maximum stress (σmax) with small increases in moisture content were found for films made of pullulan or pullulan mixed with 15% DM sorbitol; a strong softening effect was observed when the water content exceeded this range. Addition of sorbitol increased the water vapour transmission rate of the films, whereas addition of SE had the opposite effect. Application of a pullulan/sorbitol/SE coating on strawberries resulted in large changes in internal fruit atmosphere composition which were beneficial for extending the shelf‐life of this fruit; the coated fruit showed much higher levels of CO2, a large reduction in internal O2, better firmness and colour retention and a reduced rate of weight loss. In contrast, similar studies on whole kiwifruits showed increased levels of internal ethylene, which caused acceleration of fruit ripening during storage.© 2001 Society of Chemical Industry

Aminoethoxyvinylglycine, Combined with Ethephon, Can Enhance Red Color Development without Over-ripening Apples

AVG, as ReTain™, an inhibitor of ethylene biosynthesis, was used alone or with a subsequent application of ethephon (Ethrel™), an ethylene-releasing chemical, to determine if red color development could be enhanced without over-ripening `Gala' and `Jonagold' apples. Treatments included: 1) AVG alone; 2) AVG followed by ethephon; 3) ethephon alone; and 4) control. Silwet L-77 surfactant was included in all treatments. Application of AVG delayed the onset of the ethylene climacteric and red color development of both cultivars. Application of AVG followed by ethephon similarly delayed the onset of the ethylene climacteric, but red color development at the commercial harvest date was only marginally reduced or not affected. The results were similar in both 1998 and 1999, although environmental stress during the growing seasons differed (1998—heat; 1999—moderate temperatures). The delay of fruit maturation and ripening observed at harvest following AVG +/- ethephon treatments improved storability of fruit in controlled atmosphere (CA) storage, as demonstrated by low internal ethylene levels after storage, and high retention of flesh firmness and shelf-life, while control fruit and those treated only with ethephon entered the ethylene climacteric during storage, and flesh firmness subsequently declined during shelf-life evaluation. Chemical name used: aminoethoxyvinylglycine (AVG).

Acetolactate Synthase Inhibitors Increase Ethylene Production and Cause Fruit Drop in Citrus

The abscission action of two sulfonylureas and one imidazolinone was evaluated in laboratory studies with harvested orange (Citrus sinensis L. cv. Valencia) fruit and greenhouse studies with orange (cv. Hamlin) and grapefruit (Citrus paradisi Macf. cv. Marsh) trees. Dipping harvested fruit in 90 mg·L–1 imazameth, 2 mg·L–1 metsulfuronmethyl, or 30 mg·L–1 prosulfuron solutions increased levels of internal ethylene. Internal ethylene concentration was higher when fruit were dipped in 2 mg·L–1 metsulfuron-methyl solutions at low pH. Fruit retained on trees and dipped in 2 mg·L–1 metsulfuron-methyl solutions produced more ethylene than control fruit. Drop of treated fruit began when ethylene production was at a maximum. High temperatures (average 33 °C) suppressed ethylene production and fruit drop of metsulfuron-methyl–treated fruit. The results indicate the importance of environmental conditions in evaluating the potential of sulfonylureas and imidazolinones as abscission agents for citrus. Chemical names used: ±-2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-5-methyl-3-pyridinecarboxylic acid (imazameth); methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2yl) amino] carbonyl] amino] sulfonyl] benzoate (metsulfuron-methyl); 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[2-(3,3,3-trifluoropropyl) phenylsulfonyl] urea (prosulfuron); N-(phosphonomethyl) glycine (glyphosate); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1 H-imidazol-2-yl]-3-quinolinecarboxylic acid (imazaquin).

532 Lovastatin Inhibits α-Farnesene Synthesis without Affecting Ethylene Production during Fruit Ripening in Apples

At harvest, internal ethylene was &gt;0.5 mL·L–1 and α-farnesene concentrations were below detectable levels in `Golden Supreme', `Delicious', and `Granny Smith' apples. After 30 days of storage at 20 °C, control fruit produced high levels of internal ethylene and α-farnesene. Lovastatin at 100 to 1000 mL·L–1 did not affect ethylene synthesis, but significantly inhibited α-farnesene production. In `Golden Delicious', ethephon treatment increased ethylene synthesis in lovastatin-treated fruit but did not stimulate α-farnesene production. In lovastatin-treated fruit peel of `Delicious' and `Granny Smith', mevalonate (MAL) and farnesyl pyrophosphate (FPP) induced α-farnesene production, but hydroxymethylglutaric acid (HMG) did not. The induction of α-farnesene synthesis by MAL and FPP was concentration-dependent. Precursor feeding did not affect ethylene production in fruit peel. When high level of α-farnesene was detected in fruit peel (5 mm thick), it was not found in outer (adjacent to peel) and inner cortex (mid of flesh) tissues. Adding HMG, MAL, and FPP induced α-farnesene biosynthesis in both cortex tissues. When lovastatin was added to the feeding solution, MAL and FPP induced α-farnesene production but HMG did not.

The Degreening of `Fallglo' Tangerine

`Fallglo' (Bower citrus hybrid [Citrus reticulata Blanco × (C. reticulata Blanco × C. paradisi Macf.)] × `Temple' [C. reticulata Blanco × C. sinensis L.] is an early season tangerine that is reportedly hypersensitive to ethylene exposure during degreening. The effects of ethylene exposure time, waxing, and storage temperature on `Fallglo' color were examined to assess degreening strategies. Exposure to 5 μL·L-1 ethylene for 24 or 48 hours hastened degreening, and internal ethylene levels increased following the time periods of ethylene exposure. Fruit not exposed to ethylene, or exposed for shorter periods (2 or 6 hours), degreened slowly during storage at 15.5 °C and internal ethylene levels remained low. Low-temperature storage (4.5 °C) or waxing hindered degreening after ethylene exposure but decreased water loss. Degreening after ethylene exposure was faster for fruit stored at 15.5 than 26.5 °C.

Induction of chitinase and β-1,3-glucanase activity in sunflower suspension cells in response to an elicitor fromPhytophthora megaspermaf. sp.glycinea(Pmg). Evidence for regulation by ethylene and 1-aminocyclopropane-1-carboxylic acid (ACC)

In heterotrophic cell suspensions of sunflower (Helianthus annuus L. cv. Spanners Allzweck) the effect of Pmg elicitor, a fungal elicitor preparation from Phytophthora megasperma f. sp. glycinea, on the induction of chitinase and /?-1 ,3-glucanase activity was studied in relation to changes in ethylene biosynthesis. Dose-response experiments with Pmg elicitor showed that the onset of the induction of intracellular chitinase and /M ,3-glucanase activity coincided or followed a transient rise in ethylene and particularly endogenous 1-aminocyclopropane-1-carboxylic acid (ACC) levels within 5 h of application. Treatment with 5 /*g ml 1 elicitor stimulated ethylene and ACC levels 1.6-fold and 4-fold, relative to control, respectively. The molar ratio of ACC to ethylene changed from approximately 3:1 in controls to 9:1 in treated cells. During further incubation, ethylene formation and, to a lesser degree, ACC levels declined and the ACC/ethylene ratio increased to 56:1 in elicitor-treated cells. On a protein basis, the activities of /M ,3-glucanase and chitinase increased approximately 5-fold and 8-fold, respectively, 48 h after elicitor application. Additional treatment with the ACC synthesis inhibitor aminoethoxyvinylglycine (AVG) decreased elicitorinduced enzyme activities and the levels of both ethylene and ACC. Elicitor effects on chitinase and /M ,3-glucanase activities could be fully restored when ACC was additionally applied. Concomitantly, the ACC/ ethylene ratio increased. Neither treatments with ACC alone, which simultaneously increased internal ACC and ethylene levels, nor treatments with AVG alone, which simultaneously reduced ACC and ethylene levels, could generally stimulate chitinase or /M ,3-glucanase activities in the cells. It is suggested that ACC functions as a promoting factor in the induction of chitinase and /M ,3-glucanase activity triggered by Pmg elicitor and appears to reverse an inhibiting influence of ethylene.

Ethylene Biosynthesis and Accumulation under Drained and Submerged Conditions (A Comparative Study of Two Rumex Species).

A model is presented of the regulation of ethylene biosynthesis in relation to submergence and flooding resistance. It is based on time-course measurements of ethylene production, ethylene accumulation, and concentrations of free and conjugated 1-aminocyclo-propane-1-carboxylic acid (ACC) in submerged and drained flooding-resistant Rumex palustris Sm. and flooding-sensitive Rumex acetosella L. plants. From these data, in vivo reaction rates of the final steps in the ethylene biosynthetic pathway were calculated. According to our model, submergence stimulates ACC formation and inhibits conversion of ACC to ethylene in both Rumex species, and as a result, ACC accumulates. This may explain the stimulated ACC conjugation observed in submerged plants. Although submergence inhibited ethylene production, physical entrapment increased endogenous ethylene concentrations in both flooding-resistant R. palustris and flooding-sensitive R. acetosella plants. However, R. palustris plants controlled their internal ethylene levels in the long term by a negative regulation of ACC synthase induced by ethylene. In flooding-sensitive R. acetosella plants, absence of negative regulation increased internal ethylene levels to more than 20 [mu]L L-1 after 6 d of submergence. This may accelerate the process of senescence and contribute to their low level of flooding resistance.