Absence Of Exogenous Ethylene Research Articles

Evidence of the functional role of the ethylene receptor genes SlETR4 and SlETR5 in ethylene signal transduction in tomato.

Ethylene receptors are key factors for ethylene signal transduction. In tomato, six ethylene receptor genes (SlETR1-SlETR6) have been identified. Mutations in different ethylene receptor genes result in different phenotypes that are useful for elucidating the roles of each gene. In this study, we screened mutants of two ethylene receptor genes, SLETR4 and SLETR5, from a Micro-Tom mutant library generated by TILLING. We identified two ethylene receptor mutants with altered phenotypes and named them Sletr4-1 and Sletr5-1. Sletr4-1 has a mutation between the transmembrane and GAF domains, while Sletr5-1 has a mutation within the GAF domain. Sletr4-1 showed increased hypocotyl and root lengths, compared to those of wild type plants, under ethylene exposure. Moreover, the fruit shelf life of this mutant was extended, titratable acidity was increased and total soluble solids were decreased, suggesting a reduced ethylene sensitivity. In contrast, in the absence of exogenous ethylene, the hypocotyl and root lengths of Sletr5-1 were shorter than those of the wild type, and the fruit shelf life was shorter, suggesting that these mutants have increased ethylene sensitivity. Gene expression analysis showed that SlNR was up-regulated in the Sletr5-1 mutant line, in contrast to the down-regulation observed in the Sletr4-1 mutant line, while the down-regulation of SlCTR1, SlEIN2, SlEIL1, SlEIL3, and SlERF.E4 was observed in Sletr4-1 mutant allele, suggesting that these two ethylene receptors have functional roles in ethylene signalling and demonstrating, for the first time, a function of the GAF domain of ethylene receptors. These results suggest that the Sletr4-1 and Sletr5-1 mutants are useful for elucidating the complex mechanisms of ethylene signalling through the analysis of ethylene receptors in tomato.

Evaluation of a Sprayable Formulation of 1-Methylcyclopropene in Floriculture

We conducted a series of studies to determine the efficacy of a sprayable formulation of 1-methylcyclopropene (1-MCP; AFxRD-038) to inhibit ethylene-mediated flower abscission in Impatiens walleriana. Exposing Impatiens plants to 1.0 μL·L−1 ethylene for 18 hours caused complete abscission of open flowers and most buds. Sprays of the novel 1-MCP formulation at concentrations >2.5 mg·L−1 protected plants from ethylene. At 5 and 10 mg·L−1, the efficacy of 1-MCP increased as spray volume increased from 102 mL·m−2 to 306 mL·m−2. 1-MCP was rainfast with no decrease in efficacy resulting from heavy overhead irrigation within 1–2 minutes of application. Prepared 1-MCP solutions (10 mg·L−1) remained effective up to 2 weeks after mixing if held in airtight containers. The sprayable 1-MCP formulation provided protection against exogenous ethylene for a maximum of 4 days and reduced stress-related abscission from 3 days of darkness (in the absence of exogenous ethylene) at 20 °C or 40 hours darkness at 28 °C.

The effects of ethylene, 1-MCP and AVG on sprouting in sweetpotato roots

Exogenous ethylene is commonly used as a commercial sprouting inhibitor of potato tubers. The role of ethylene in the control of sprouting of sweetpotato roots, however, is not known. The aim of this study was to investigate the role of ethylene in control of sprouting in sweetpotato roots by observing the effect of an ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG), and the ethylene antagonist, 1-methylcyclopropene (1-MCP), in the presence and absence of exogenous ethylene on root sprouting and associated sugar accumulation. Continuous exposure to 10μlL−1 ethylene, 24h exposure to 625nlL−1 1-MCP or dipping in 100μlL−1 AVG all inhibited sprout growth in sweetpotato roots of two varieties over 4 weeks of storage at 25°C. The observations that both ethylene on its own and 1-MCP, which inhibits ethylene action, inhibit sprout growth indicate that while continuous exposure to exogenous ethylene leads to sprout growth inhibition, ethylene is also required for sprouting. In potato tubers ethylene is required to break dormancy, while continuous exposure inhibits sprout growth.Monosaccharide concentrations in ethylene, 1-MCP or AVG treated roots were lower than in untreated roots, and for ethylene treated roots this was associated with higher respiration rates. This is consistent with the activation of some additional process by ethylene which uses energy through sugar metabolism. 1-MCP and AVG both inhibited this increase in respiration rate and counteracted the decrease in monosaccharide concentrations. 1-MCP presumably counteracts the ethylene stimulation of this process, while the effect of AVG is attributed to its possible inhibitory effects on protein synthesis.

Influence of Humidity and Temperature on Postharvest Needle Abscission in Balsam Fir in the Presence and Absence of Exogenous Ethylene

Ethylene accumulation increases after harvest and culminates in needle abscission in balsam fir [Abies balsamea (L.) Mill.]. We hypothesize that water deficit induces ethylene evolution, thus triggering abscission. The purpose of this research was to investigate the role of temperature and humidity on postharvest needle abscission in the presence and absence of exogenous ethylene and link vapor pressure deficit (VPD) to postharvest needle abscission in balsam fir. In the first experiment, branches were exposed to 30%, 60%, or 90% humidity while maintained at 19.7 °C (VPD of 1.59, 0.91, or 0.23 kPa, respectively); in the second experiment, branches were exposed to 5, 15, or 25 °C (VPD of 0.35, 0.68, or 1.26 kPa, respectively) while maintained at 60% relative humidity. Needle retention duration, average water use, xylem pressure potential relative water content, and ethylene evolution were response variables. Reducing water loss or xylem tension by changing temperature or humidity effectively delayed needle abscission, although the 90% humidity treatment had the most profound effects. In the absence of exogenous ethylene, branches placed in 90% humidity had a fivefold increase in needle retention, 67% decrease in average water use, and had a final xylem pressure potential of –0.09 MPa. There was a near perfect relationship between VPD and needle retention (R2 = 0.99). These findings suggest that increasing xylem tension or decreasing water status may trigger ethylene synthesis and needle abscission. In addition, these findings demonstrate an effective means of controlling postharvest needle abscission by modifying temperature and/or relative humidity.

Ethylene triggers needle abscission in root-detached balsam fir

Post-harvest needle abscission is a major challenge for Christmas tree and greenery industries. It was hypothesized that ethylene triggers abscission in balsam fir. Three experiments were conducted to test this hypothesis. In experiment 1, 70 balsam fir branches were collected, placed in water, and ethylene evolution was observed over time. In experiment 2, a 2 9 5 factorial experiment was designed to determine the effect of exogenous ethylene and an ethylene receptor blocker, 1-methylcyclopropene (1- MCP), on needle abscission. In experiment 3, a 2 9 6 factorial experiment was designed to determine the effect of exogenous ethylene and an ethylene inhibitor, amino- ethoxyvinylglycine (AVG), on needle abscission. It was found that ethylene evolution was the highest 1-2 days prior to needle abscission, which was consistent in untreated branches and branches exposed to exogenous ethylene. Exposure to exogenous ethylene significantly decreased needle retention by 63%. When ethylene receptors were blocked by 1-MCP, needle retention increased by 147% despite the presence of ethylene and increased by 73% in the absence of ethylene when com- pared to the respective controls. When endogenous ethyl- ene synthesis was inhibited by AVG, there was no improvement in needle retention in the presence of ethyl- ene, but there was a 113% increase in needle retention in the absence of exogenous ethylene. Ethylene is strongly implicated as the signal triggering abscission in root- detached balsam fir.

Arabidopsis EIN3-binding F-box 1 and 2 form ubiquitin-protein ligases that repress ethylene action and promote growth by directing EIN3 degradation.

Ubiquitination of various intracellular proteins by ubiquitin-protein ligases (or E3s) plays an essential role in eukaryotic cell regulation primarily through its ability to selectively target proteins for degradation by the 26S proteasome. Skp1, Cullin, F-box (SCF) complexes are one influential E3 class that use F-box proteins to deliver targets to a core ligase activity provided by the Skp1, Cullin, and Rbx1 subunits. Almost 700 F-box proteins can be found in Arabidopsis, indicating that SCF E3s likely play a pervasive role in plant physiology and development. Here, we describe the reverse genetic analysis of two F-box proteins, EBF1 and -2, that work coordinately in SCF complexes to repress ethylene action. Mutations in either gene cause hypersensitivity to exogenous ethylene and its precursor 1-aminocyclopropane-1-carboxylic acid. EBF1 and -2 interact directly with ethylene insensitive 3 (EIN3), a transcriptional regulator important for ethylene signaling. Levels of EIN3 are increased in mutants affecting either EBF1 or -2, suggesting that the corresponding SCF complexes work together in EIN3 breakdown. Surprisingly, double ebf1 ebf2 mutants display a substantial arrest of seedling growth and have elevated EIN3 levels, even in the absence of exogenous ethylene. Collectively, our results show that the SCF(EBF1/EBF2)-dependent ubiquitination and subsequent removal of EIN3 is critical not only for proper ethylene signaling but also for growth in plants.

Effect of octanoic acid on ethylene-mediated processes in Arabidopsis

We have examined whether octanoic acid (OA) one of the short chain saturated fatty acids (SCSFA), increases ethylene response in the following three ethylene-mediated processes: a) hypocotyl growth in darkness; b) formation of new flowers; c) flower abscission. These processes were examined in the presence or absence of exogenous ethylene in Arabidopsis wild type (WT) and in the ethylene-insensitive mutants, etr1-3 and ein2-1 and in the ethylene over-producer mutant eto1-1. Our results show that OA decreased hypocotyl length of WT in the absence or presence of exogenous ethylene, apparently showing that OA acts via augmentation of ethylene action. However, the hypocotyl growth inhibition could not be ascribed to increased ethylene sensitivity since application of inhibitors of ethylene synthesis (aminoethoxyvinylglycine; AVG) or action (1-methylcyclopropene;1-MCP) to WT seedlings did not prevent specifically the OA-induced growth inhibition. Also, OA inhibited hypocotyl growth in the mutants etr1-3 and ein2-1 in a similar pattern to that obtained in WT. On the other hand, OA had no effect on flower formation neither in WT, etr1-3 and eto1-1, in which ethylene reduced flower formation, nor in the ein2-1 mutant, in which ethylene had no effect. OA also did not increase flower abscission in WT or in the mutants etr1-3 and ein2-1 neither in the absence nor in the presence of ethylene. However, OA has augmented flower abscission in the mutant eto1-1 only in the absence of exogenous ethylene. This result might indicate that the effect of OA on eto1-1 is specific to this mutant and is not due to general deleterious effects inflicted by OA. Taken together, our results show that in general OA does not augment ethylene response in Arabidopsis, but it might affect ethylene action in flower abscission of the ethylene-overproducer mutant.

Postharvest Handling of Stock (Matthiola incana)

The respiration of flowers of stock [Matthiola incana (L.) R. Br.] had a Q10 of 6.9 between 0 and 10 °C. Simulated transport for 5 days resulted in marked reduction in the vase life of flowers transported at 10 °C and above. Flower opening, water uptake, and vase life of the flowers increased somewhat in a vase solution containing 50 ppm NaOCl, and considerably in a commercial preservative containing glucose and a bactericide. Exposure to exogenous ethylene resulted in rapid desiccation and abscission of the petals, effects that were prevented by pretreatment with 1-methylcyclopropene (1-MCP). Even in the absence of exogenous ethylene, the life of the flowers was significantly increased by inhibiting ethylene action using pretreatment with silver thiosulfate (STS) or 1-MCP. STS was more effective than 1-MCP in maintaining flower quality.

Responses of Native Australian Cut Flowers to Treatment with 1-Methylcyclopropene and Ethylene

Postharvest longevity of some cut flowers is shortened by exposure to ethylene gas. Adverse effects of ethylene may be prevented by treatment with 1-methylcyclopropene (1-MCP) gas. Responses of 14 different native Australian cut flowers to 1-MCP and ethylene applied at concentrations of 10 nL·L-1 and 10 μL·L-1, respectively, were examined. Each gas was applied alone for 12 hours at 20 °C and they were also applied in series. Vase lives of Ceratopetalum gummiferum, Chamelaucium uncinatum, Grevillea `Kay Williams' and `Misty Pink', Leptospermum petersonii, Telopea `Shady Lady', and Verticordia nitens were reduced by ethylene treatment. Treatment with 1-MCP generally protected these cut flowers against subsequent exposure to ethylene. The 1-MCP treatment usually did not extend their vase lives in the absence of exogenous ethylene.

Molecular and genetic characterization of a novel pleiotropic tomato-ripening mutant

In this paper we describe a novel, dominant pleiotropic tomato (Lycopersicon esculentum)-ripening mutation, Cnr (colorless nonripening). This mutant occurred spontaneously in a commercial population. Cnr has a phenotype that is quite distinct from that of the other pleiotropic tomato-ripening mutants and is characterized by fruit that show greatly reduced ethylene production, an inhibition of softening, a yellow skin, and a nonpigmented pericarp. The ripening-related biosynthesis of carotenoid pigments was abolished in the pericarp tissue. The pericarp also showed a significant reduction in cell-to-cell adhesion, with cell separation occurring when blocks of tissue were incubated in water alone. The mutant phenotype was not reversed by exposure to exogenous ethylene. Crosses with other mutant lines and the use of a restriction fragment length polymorphism marker demonstrated that Cnr was not allelic with the pleiotropic ripening mutants nor, alc, rin, Nr, Gr, and Nr-2. The gene has been mapped to the top of chromosome 2, also indicating that it is distinct from the other pleiotropic ripening mutants. We undertook the molecular characterization of Cnr by examining the expression of a panel of ripening-related genes in the presence and absence of exogenous ethylene. The pattern of gene expression in Cnr was related to, but differed from, that of several of the other well-characterized mutants. We discuss here the possible relationships among nor, Cnr, and rin in a putative ripening signal cascade.

Fructose 2,6-bisphosphate and the climacteric in bananas.

This work was done to test the view that there is a marked rise in the content of fructose 2,6-bisphosphate during the climacteric of the fruit of banana (Musa cavendishii Lamb ex. Paxton). Bananas were ripened in the dark in a continuous stream of air in the absence of exogenous ethylene. CO2 production and the contents of fructose 2,6-bisphosphate and sucrose were monitored over a 15-day period. A range of extraction procedures for fructose 2,6-bisphosphate were compared. Recovery of fructose 2,6-bisphosphate added to samples of unripe fruit varied from poor to unmeasurable. Recoveries from samples of ripe fruit were high. It is argued that this differential recovery of fructose 2,6-bisphosphate undermines claims that the amount of this compound increases at the climacteric. When recoveries are taken into account, our data suggest that there is no major change in fructose 2,6-bisphosphate content during the onset of the climacteric in bananas.

An Evaluation of 2,5-Norbornadiene as a Reversible Inhibitor of Ethylene Action in Deepwater Rice

Partial submergence of deepwater rice (Oryza sativa L. cv Habiganj Aman II) elicits three responses: enhancement of internodal elongation, inhibition of leaf growth, and promotion of adventitious root formation. All three responses can be induced in isolated stem sections by treatment with ethylene. Dose-response curves indicate that the responses are linearly related to the logarithm of the ethylene concentration over two orders of magnitude. Application of the cyclic olefin 2,5-norbornadiene (NBD) to ethylene-treated sections results in a parallel shift in dose-response curves to higher ethylene concentrations, indicating that NBD behaves as a competitive inhibitor of ethylene action. Internodal elongation of stem sections is promoted by gibberellic acid (GA(3)) in the absence of exogenous ethylene. Endogenous ethylene levels do not increase in GA(3)-treated sections, and application of NBD does not prevent GA(3)-promoted elongation. To the contrary, NBD treatment results in increased growth at intermediate GA(3) concentrations. These results support the idea that ethylene acts through endogenous GA in promoting growth in deepwater rice. NBD applied to GA(3)-treated stem sections results in increased ethylene production. This enhancement of ethylene formation is reversed by application of either ethylene or propylene, indicating that ethylene biosynthesis in rice internodes is under negative feedback control.

Ethylene-promoted tomato flower abscission and the possible involvement of an inhibitor

The abscission zone in tomato (Lycopersicon esculentum (L.) Mill. flower pedicels is morphologically distinguishable prior to separation and is delineated by an indentation of the epidermis. Exposure of excised pedicels with the flower attached to ethylene results in abscission within 12 h and this can be accelerated by flower removal. Abscission of excised pedicels with the flower removed takes place in the absence of exogenous ethylene but this is delayed by pretreatment with aminoethoxyvinyl glycine, an inhibitor of ethylene biosynthesis. The data presented support the hypothesis that flower tissue is the source of an abscission inhibitor.

Involvement of Ethylene in Chlorophyll Degradation in Peel of Citrus Fruits

The effect of ethylene on chlorophyll degradation in the peel of Robinson tangerine (X Citrus reticulata Blanco) and calamondin (X Citrofortunellamitis [Blanco] Ingram and Moore) fruits was studied. The chlorophyll degrading system in the peel of these two citrus species was not self-sustaining but required ethylene to function. Chlorophyll degradation ceased immediately when fruit were removed from ethylene and held in ethylene-free air at 0.2 atmospheric pressure. However, at atmospheric pressure, chlorophyll degradation continued for 24 hours in the absence of exogenous ethylene. Although chlorophyllase levels were negatively correlated with chlorophyll content in the peel (r = -0.981; P < 0.01), the level of chlorophyllase activity did not change when fruit were removed from ethylene, even though chlorophyll degradation had stopped. From these observations, it was concluded that ethylene is necessary for chlorophyll degradation in the two species of citrus studied, but its primary role is not solely for the induction of chlorophyllase activity.

Involvement of Endogenous Ethylene in the Induction of Color Change in Shamouti Oranges

Reducing the level of endogenous ethylene in detached Shamouti oranges (Citrus sinensis L. Osbeck) by means of subatmospheric pressure did not alter the rate of chlorophyll destruction and color changes during the first 8 days after harvest in the presence or absence of exogenous ethylene. Reducing the activity of ethylene by means of CO(2)-known to be a competitive inhibitor for ethylene-inhibited chlorophyll destruction and color change in Shamouti oranges ventilated with ethylene, but had no effect on these processes in the absence of applied ethylene. The evidence presented indicates that endogenous ethylene may not be the primary inducer for the natural color change in detached Shamouti oranges.