Role Of Ethylene Research Articles

Cell wall disassembly during papaya softening: Role of ethylene in changes in composition, pectin-derived oligomers (PDOs) production and wall hydrolases

Cell wall disassembly in ripening climacteric fruit is a highly complex process where ethylene plays a crucial role. Ethylene inhibitors can be used to explore the changes in the cell wall matrix and cross-linked polysaccharides in ethylene-regulated processes. The results of applying the ethylene receptor blocking inhibitor 1-methylcyclopropene (1-MCP) and the ethylene-releasing compound ethephon (2-chloroethylphosphonic acid) indicate that softening of ‘Maradol’ papaya fruit is dependent on ethylene. When fruit were induced to ripen extensively by exposure to a high dose of ethephon, 1-MCP inhibited the subsequent softening dramatically, but when inhibition of the ethylene response was caused by application of 1-MCP, subsequent fruit treatment with ethephon promoted extensive loss of galactose from the water-soluble polysaccharides, but this was not accompanied by fruit softening. The cell wall changes accompanying normal fruit softening were pectin solubilization and polyuronide depolymerization and these processes occurred simultaneously. Polygalacturonase likely is responsible for the ripening-associated changes in ‘Maradol’ papaya fruit texture and pectin polymer integrity. An increase in extractable fruit polygalacturonase follows the increased presence of pectin-derived oligosaccharides.

Ethylene insensitivity impedes a subset of responses to phosphorus deficiency in tomato and petunia

The role of ethylene in growth and developmental responses to low phosphorus stress was evaluated using ethylene-insensitive 'Never-ripe' (Nr) tomato and etr1 petunia plants. Low phosphorus increased adventitious root formation in 'Pearson' (wild-type) tomato plants, but not in Nr, supporting a role for ethylene in adventitious root development and showing that ethylene is important for this aspect of phosphorus response. Low phosphorus reduced ethylene production by adventitious roots of both genotypes, suggesting that ethylene perception--not production--regulates carbon allocation to adventitious roots at the expense of other roots under low phosphorus stress. With the exception of its effect on adventitious rooting, Nr had positive effects on growth and biomass accumulation in tomato whereas etr1 tended to have negative effects on petunia. This was particularly evident during the recovery from transplanting, when the effective quantum yield of photosystem II of etr1 petunia grown with low phosphorus was significantly lower than 'Mitchell Diploid', suggesting that etr1 petunia plants may undergo more severe post-transplant stress at low phosphorus availability. Our results demonstrate that ethylene mediates adventitious root formation in response to phosphorus stress and plays an important role for quick recovery of plants exposed to multiple environmental stresses, i.e. transplanting and low phosphorus.

Exogenous ethylene inhibits sprout growth in onion bulbs

Exogenous ethylene has recently gained commercial interest as a sprouting inhibitor of onion bulbs. The role of ethylene in dormancy and sprouting of onions, however, is not known. A cultivar (Allium cepa 'Copra') with a true period of dormancy was used. Dormant and sprouting states of onion bulbs were treated with supposedly saturating doses of ethylene or with the ethylene-action inhibitor 1-methylcyclopropene (1-MCP). Initial sprouting was determined during storage at 18 degrees C by monitoring leaf blade elongation in a specific size class of leaf sheaths. Changes in ATP content and sucrose synthase activity in the sprout leaves, indicators of the sprouting state, were determined. CO(2) and ethylene production of onion bulbs during storage were recorded. Exogenous ethylene suppressed sprout growth of both dormant and already sprouting onion bulbs by inhibiting leaf blade elongation. In contrast to this growth-inhibiting effect, ethylene stimulated CO(2) production by the bulbs about 2-fold. The duration of dormancy was not significantly affected by exogenous ethylene. However, treatment of dormant bulbs with 1-MCP caused premature sprouting. Exogenous ethylene proved to be a powerful inhibitor of sprout growth in onion bulbs. The dormancy breaking effect of 1-MCP indicates a regulatory role of endogenous ethylene in onion bulb dormancy.

Activation and manipulation of host responses by a Gram-positive bacterium

The interaction between tomato plants and Clavibacter michiganensis subsp. michiganensis (Cmm) represents a model pathosystem to study the interplay between the virulence determinants of a Gram-positive bacterium and the attempt of a crop plant to counteract pathogen invasion. To investigate plant responses activated during this compatible interaction, we recently analyzed gene expression profiles of tomato stems infected with Cmm. This analysis revealed activation of basal defense responses that are typically observed upon plant perception of pathogen-associated molecular patterns. In addition, Cmm infection upregulated the expression of host genes related to ethylene synthesis and response. Further analysis of tomato plants impaired in ethylene perception and production demonstrated an important role for ethylene in the development of disease symptoms. Here we discuss possible molecular strategies used by the plant to recognize Cmm infection and possible mechanisms employed by the pathogen to interfere with the activation of plant defense responses and promote disease.Addendum to: Balaji V, Mayrose M, Sherf O, Jacob-Hirsch J, Eichenlaub R, Iraki N, Manulis-Sasson S, Rechavi G, Barash I, Sessa G. Tomato transcriptional changes in response to Clavibacter michiganensis subsp. michiganensis reveal a role for ethylene in disease development. Plant Physiol 2008; In press.

New insights into the roles of ethylene and jasmonic acid in the acquisition of selenium resistance in plants

In a recent paper, we reported that both ethylene and jasmonic acid (JA) are important for selenium (Se) resistance in Arabidopsis.1 Elevated levels of reactive oxygen species were associated with ethylene and JA production in a Se-resistant Arabidopsis ecotype. Here, we further discuss the functions of these phytohormones, and their possible interactions, in plant Se resistance and –accumulation, placing our data in a broader perspective of other recently published papers.Addendum to: Tamaoki M, Freeman JL, Pilon-Smits EAH. Cooperative ethylene and jasmonic acid signaling regulates selenite resistance in Arabidopsis thaliana. Plant Physiol 2008;146:1219-30.

Genetic background affects genetically modified ethylene sensing in birch–insect interaction

Several studies suggest that ethylene is involved in the responses and resistance of plants against herbivores and pathogens, but the role of ethylene seems to vary depending on the system studied. Here we extend the studies of introduced Arabidopsis thaliana (L.) Heynh. ethylene receptor gene (etr1-1) to a new type of interaction: a woody plant, Betula pendula Roth (silver birch) and its herbivore, Epirrita autumnata (Borkhausen) (autumnal moth). We studied constitutive insect resistance of two wild-type birch genotypes, V and J, which were very different hosts for E. autumnata. On the J background, genetically modified ethylene insensitivity decreased the performance of E. autumnata, measured as leaf damage, larval mass, or pupal mass. However, hardly any changes were detectable in the V background, which is an inferior wild-type genotype for autumnal moth performance, except increased leaf damage caused by E. autumnata in ethylene-insensitive trees. Ethylene insensitivity caused clear side effects on birch phenology and morphology, especially in the J background. In this background, ethylene modification mainly acted via accelerating phenology, but this was hardly detectable in the V genotype. Also, the number of long shoots increased only in the modified J background. Taken together, it seems that the effects of ethylene on several birch traits relevant for E. autumnata and birch morphology depend on the birch genetic background.

Correlation of ethylene synthesis in Citrus fruits and their susceptibility to Alternaria alternata pv. citri

The susceptibility of Fortune ( Citrus clementina × Citrus reticulata), Citrus paradisi and Citrus limon fruits to Alternaria alternata pv. citri was investigated using different artificial inoculation methods. The results obtained reveal that the C. paradisi and C. limon fruits are less susceptible to A. alternata pv. citri than Fortune fruits, although all showed symptoms of Alternaria brown spot when the cuticle was broken and the flavedo or flavedo + albedo was removed. Furthermore, it was seen that susceptibility to the fungus decreased as the age of the fruit increased. There was a positive correlation between the susceptibility of the different Citrus fruits to A. alternata pv. citri and their “in vivo” ethylene levels, the most susceptible fruit (Fortune) producing more ethylene during growth than the less susceptible C. limon and C. paradisi. This suggests that ethylene may well be considered as a possible marker of Citrus fruit susceptibility to A. alternata pv. citri. Disease development increased when the Fortune fruits were treated with 1 mM ACC (a precursor of ethylene biosynthesis) or 1 mM Ethephon (an ethylene-releasing compound) prior to inoculation with A. alternata pv. citri. The role of ethylene as a factor involved in disease development is discussed.

Generation of expressed sequence tags from carob (Ceratonia siliqua L.) flowers for gene identification and marker development

Carob (Ceratonia siliqua L.) is a caesalpinoid legume tree showing labile sex expression. With the main aims of identifying flower-expressed genes and of developing specific markers, 1,056 clones from a complementary DNA library of carob flowers were bidirectionally sequenced. A total of 1,377 high-quality expressed sequence tags were clustered into 1,096 unigenes. Basic Local Alignment Search Tool and Gene Ontology functional annotation allowed to identify several agronomically important genes, such as those involved in flower development and sexual reproduction, response to stress, galactomannan synthesis, and hormone pathways. Genes involved in the ethylene biosynthesis and response were quantified in developing flowers of three sex genotypes (male, female, and hermaphrodite) using quantitative reverse transcription polymerase chain reaction. The transcript levels of 1-aminocyclopropane-1-carboxylic acid oxidase, acting downstream in ethylene pathway, and Ethylene Insensitive 3 (EIN3)-like, a transcription factor involved in ethylene signaling, were directly correlated with maleness, indicating a possible role of ethylene in carob sex expression. Furthermore, the first set of carob genic microsatellites was developed, which might be useful for genotyping and genetic diversity analysis.

Improvement in Cadmium Tolerance of Tomato Seedlings with an Antisense DNA for 1-Aminocyclopropane-1-Carboxylate Synthase

ABSTRACT Cadmium (Cd) accelerates leaf senescence and causes cell death in plants. However, the role of ethylene in these responses is currently unclear. In the present study, expressing an antisense 1-aminocyclopropane-1-carboxylic acid synthase gene (LeACS2) reduced the LeACS2 message by 89% under Cd stress, which blocked ethylene evolution in tomato (Lycopersicon esculentum). Cadmium-induced cell death was attenuated in LeACS2 antisense plants, which was complemented by pretreatment of ethylene precursor, suggesting ethylene is required for Cd-induced cell death. The function of ethylene in cell death is hydrogen peroxide (H2O2)-dependent. Ethylene blocking inhibited Cd-induced H2O2 accumulation. Application of H2O2-generating Glc/Glc oxidase promoted cell death in wild-type and LeACS2 antisense plants. Cadmium caused loss of chlorophyll and foliar protein, which was retarded in LeACS2 antisense plants. The LeACS2 antisense plants maintained leaf performance, including transpiration and CO2 assimilate. These results define a regulatory role of ethylene in the regulation of cell death and leaf performance under Cd stress.

Synergistic interactions between the ACC deaminase-producing bacterium Pseudomonas putida UW4 and the AM fungus Gigaspora rosea positively affect cucumber plant growth

Bacteria producing 1-aminocyclopropane-1-carboxylate (ACC) deaminase modulate plant ethylene levels. Decreased ethylene levels increase plant tolerance to environmental stresses and promote legume nodulation. On the contrary, the role of ethylene in mycorrhizal symbiosis establishment is still controversial. In this work, the ACC deaminase-producing strain Pseudomonas putida UW4 AcdS+ and its mutant AcdS(-), impaired in ACC deaminase synthesis, were inoculated alone or in combination with the AM fungus Gigaspora rosea on cucumber. Mycorrhizal and bacterial colonization as well as plant growth and morphometric parameters were measured. The influence of each microorganism on the photosynthetic efficiency was evaluated on the second and fourth leaf. The strain AcdS+, but not the AcdS(-) mutant, increased AM colonization and arbuscule abundance. The mycorrhizal fungus, but not the bacterial strains, promoted plant growth. However, the AcdS+ strain, inoculated with G. rosea, induced synergistic effects on plant biomass, total root length and total leaf projected area. Finally, the photosynthetic performance index was increased by the strain UW4 AcdS+ inoculated in combination with G. rosea BEG9. These results suggest a key role of this enzyme in the establishment and development of AM symbiosis.

Role of ethylene in acclimations to promote oxygen transport in roots of plants in waterlogged soils

Ethylene plays a central role in morphological and anatomical acclimations of plants to soil waterlogging. To acclimate to waterlogging, roots of wetland species, and even some crops, form aerenchyma. Aerenchyma is large interconnected gas spaces that connect from shoot to near the tips of roots. Oxygen moves via diffusion in the root aerenchyma. In many wetland species, a barrier to radial oxygen loss (ROL) that greatly reduces oxygen leakage from basal parts, further enhances oxygen diffusion to the apex. Two main types of aerenchyma are recognized: schizogenous and lysigenous aerenchymas. Schizogenous aerenchyma is formed by cell separation without cell death. Lysigenous aerenchyma results from programmed cell death (PCD). Ethylene accumulation in plants during waterlogging induces lysigenous aerenchyma, although many wetland species form some aerenchyma even in drained conditions. The ethylene accumulation may result in the activation of G-proteins and other signal transduction cascades, of which increased cytosolic Ca 2+ is a component. Finally, PCD leading to selective cell degradation occurs in the root cortex, with cell wall degrading enzymes, such as cellulase and pectinase, also being activated. On the other hand, ethylene does not appear to induce the barrier to ROL, at least in roots of rice. Thus, induction of the barrier to ROL and formation of aerenchyma appear to be regulated by different signals. Further elucidation of signal transduction pathways initiated by ethylene sensing, as well as non-ethylene dependant responses, and of the genes regulated to control formation of the barrier to ROL and aerenchyma, should be priority areas for future research on plant tolerance of waterlogging.

Ethylene production in plants during transformation suppresses vir gene expression in Agrobacterium tumefaciens

Ethylene evolution from plants inhibits Agrobacterium-mediated genetic transformation, but the mechanism is little understood. In this study, the possible role of ethylene in Agrobacterium-mediated genetic transformation was clarified. It was tested whether or not plant ethylene sensitivity affected genetic transformation; the sensitivity might regulate bacterial growth during co-cultivation and vir gene expression in Agrobacterium tumefaciens. For these experiments, melon (Cucumis melo) was used, in which ethylene sensitivity was controlled by chemicals, and Arabidopsis ethylene-insensitive mutants. Agrobacterium-mediated genetic transformation was inhibited in ethylene-sensing melon, whereas, in Arabidopsis ethylene-insensitive mutant, it was enhanced. However, the ethylene sensitivity did not affect bacterial growth. vir gene expression was inhibited by application of plant exudate from ethylene-sensitive plants. The inhibitory effect of the ethylene sensitivity on genetic transformation relieved the activation of vir gene expression in A. tumefaciens with vir gene inducer molecule (acetosyringone, AS) or A. tumefaciens mutant strain which has constitutive vir gene expression. These results indicate that ethylene evolution from a plant inoculated with A. tumefaciens inhibited vir gene expression in A. tumefaciens through the ethylene signal transduction in the plant, and, as a result, Agrobacterium-mediated genetic transformation was inhibited.

The role of ethylene in orchid ovule development

Orchids are known for their unique reproductive biology and ecological strategies. One of the remarkable reproductive characters of most orchid species is that ovule development is precisely initiated following pollination. Thus, orchids are attractive systems for investigating both the initiation and subsequent development of the ovule. Ethylene plays a critical role in ovary maturation and ovule differentiation in orchids. Genes corresponding to ethylene biosynthesis in orchid reproductive organs have been identified and characterized. The phosphorylation states of proteins involved in ethylene biosynthesis or ethylene signaling may be correlated with ovule development. Recently, an orchid GLOBOSA-like MADS-box gene was isolated from Phalaenopsis and shown to have a role in ovule development via auxin/ethylene signaling. Adopting functional genomics strategies will help us to get insights into the regulation network between ethylene signaling pathway and ovule developmental program in orchids.

Ethylene: Fine-tuning plant growth and development by stimulation and inhibition of elongation

Plant architecture is determined by a subtle balance between growth stimulation and inhibition conferring optimal plasticity in response to environmental changes. Ethylene is a gaseous hormone which plays an essential role in a myriad of plant developmental processes, both by stimulation and inhibition of growth. Ethylene can promote root hair formation, flowering, fruit ripening and abscission, as well as leaf and petal senescence and abscission. Its role is dependent on the environmental conditions, and the plant developmental stage, besides also being species dependent. Within a plant and even within a given organ, the effect of ethylene treatment can differ, depending on endogenous and environmental cues. Moreover, ethylene signalling and response are a part of an intricate network in cross-talk with other hormones. In this review, current insights in the role of ethylene on growth processes and the influence of these different factors are discussed.

Role of ethylene in abnormal shoot growth induced by high concentration of brassinolide in rice seedlings

A high concentration of brassinolide (BL) induced abnormal shoot shape in rice seedlings, that is, the newly developed leaf sheath was shorter than the old sheath, and increased the number of leaves. The involvement of ethylene and cyanide, co-metabolites during ethylene biosynthesis, in abnormal shoot growth was analyzed by comparing the action mechanism of BL with that of quinclorac in barnyard grass seedlings. BL strongly stimulated ethylene production, and the amount of ethylene and the third leaf sheath length in rice seedlings were negatively correlated. Exogenously applied ethephon also induced abnormal growth of rice seedlings. L-α-amino-ethoxyvinyl-glycine (AVG), an ethylene biosynthetic inhibitor, partially reversed abnormal shoot growth. The level of endogenous cyanide was low in rice seedlings, because of the high level of β-cyanoalanine synthase (CAS) activity, and exogenously applied KCN did not induce abnormal shoot growth. The results indicate that BL-induced abnormal shoot growth of rice seedlings was probably mediated by ethylene production.

Ethylene is involved in vascular cavity formation in pea (Pisum sativum) primary roots

A lengthy cavity usually forms in the vascular cylinders of pea (Pisum sativum) primary roots in response to sudden flooding at 25oC. This is thought to be a form of aerenchyma. Ethylene has been shown to mediate inducible aerenchyma in maize, therefore the role of ethylene in the formation of cavities in pea roots was examined. Pea seedlings grown for 4 d in 2 L beakers in vermiculite moistened below field capacity - conditions that do not favor cavity formation - were flooded with solutions containing ethylene inhibitors (AOA, EGTA, and STS). Pea seeds were germinated and grown in suitable containers (0.8-1.0 L) for 4 d at 25oC in the dark in similar vermiculite. These were then exposed to various concentrations of ethylene for 1 d, or they were flooded and endogenous ethylene was measured periodically by gas chromatography. Observations of roots exposed to exogenous ethylene were made by light microscope. All three inhibitors of ethylene suppressed cavity formation in flooded roots. Exogenous ethylene exposure caused cavities to frequently form in a dose-dependent manner in unflooded roots and caused an increase in mean cortical cell size and number. Flooding increased the rate of ethylene release into the air space above the medium surface. These results indicate ethylene mediates vascular cavity formation and add to the evidence that vascular cavities are the result of programmed cell death and may function as a type of aerenchyma.

EGY1 plays a role in regulation of endodermal plastid size and number that are involved in ethylene-dependent gravitropism of light-grown Arabidopsis hypocotyls

Egy1 was isolated as an ethylene-dependent gravitropism-deficient Arabidopsis mutant. Molecular studies reveal that EGY1 gene encodes a 59-kDa plastid-targeted metalloprotease. It is actively expressed in hypocotyl tissue and targets to endodermal and cortex plastid. Its protein level is up-regulated by both ethylene and light. CAB protein accumulation and chlorophyll level is severely reduced in hypocotyls and endodermal cells, respectively. Sucrose is able to restore the severely reduced starch and lipid contents as well as the deficient endodermal plastid size found in light-grown egy1 hypocotyls yet it fails to rescue the reduced plastid number and chlorophyll level in egy1 endodermal cells. The loss-of-function egy1 mutation results in a smaller size (1.9 +/- 0.3 microm in diameter) and less number (5 +/- 1) of plastids in endodermal cells, which are nearly 50% of the wild-type. EGY1 is specially required for the development of full-size endodermal plastid in seedlings that are grown on sucrose-free media under light. It plays a direct role in controlling the light-induced chlorophyll production, grana formation and plastid replication in endodermal cell. However, it plays an indirect role in regulation of endodermal plastid size. It is likely that the ethylene-dependent gravitropism-deficient phenotype of egy1 hypocotyls may result from the smaller size and less number of endodermal plastids. Gravicurvature assays performed on ethylene-insensitive mutants, etr1-1, etr2-1, ers2-1, ein4-1 and ein2-5, have clearly demonstrated the necessary role for ethylene in vigorous gravitropism of light-grown hypocotyls. The degree of ethylene-dependent gravicurvature is positively correlated with the combined state of endodermal plastid mass and number. Neither ethylene nor EGY1-regulated full-size endodermal plastid is sufficient for promotion of vigorous hypocotyl gravitropism. Presence of 4 full-size plastids per endodermal cell together with ethylene pretreatment of hypocotyls becomes sufficient to trigger vigorous gravicurvature in light-grown seedlings. A model is therefore proposed to address the role of EGY1 in regulation of endodermal plastid size and number as well as the stimulatory effect of ethylene on hypocotyl gravitropism.

Reduced gibberellin response affects ethylene biosynthesis and responsiveness in the Arabidopsis gai eto2‐1 double mutant

Ethylene and gibberellins (GAs) control similar developmental processes in plants. The role of ethylene is at least in part to regulate the accumulation of DELLA proteins, key regulators of plant growth, which suppress the GA response. To expand our knowledge of ethylene-GA crosstalk and to reveal how the modulation of the ethylene and GA pathways affects global plant growth, the gibberellin-insensitive (gai), ethylene-overproducing 2-1 (eto2-1) double mutant, which has decreased GA signalling (resulting from gai) and increased ethylene biosynthesis (resulting from eto2-1), was characterized. Both single mutations resulted in reduced elongation growth. The double mutant showed synergistic responses in root and shoot growth, in induction of floral transition, and in inflorescence length, showing that crosstalk between the two pathways occurs in different plant organs throughout development. Furthermore, the altered ethylene-GA interactions affected root-shoot communication, as evidenced by an enhanced shoot:root ratio in the double mutant. When compared with both single mutants and the wild type, double mutants had enhanced content of active GA(4) at both the seedling and the rosette stages, and, unlike the gai mutant, they were sensitive to GA treatment. Finally, it was shown that synergistic responses in the double mutant were not caused by elevated ethylene biosynthesis but that, in the light, enhanced sensitivity to ethylene may, at least in part, be responsible for the observed phenotype.

Ethylene and Not Embolism Is Required for Wound-Induced Tylose Development in Stems of Grapevines

The pruning of actively growing grapevines (Vitis vinifera) resulted in xylem vessel embolisms and a stimulation of tylose formation in the vessels below the pruning wound. Pruning was also followed by a 10-fold increase in the concentration of ethylene at the cut surface. When the pruning cut was made under water and maintained in water, embolisms were prevented, but there was no reduction in the formation of tyloses or the accumulation of ethylene. Treatment of the stems with inhibitors of ethylene biosynthesis (aminoethoxyvinylglycine) and/or action (silver thiosulfate) delayed and greatly reduced the formation of tyloses in xylem tissue and the size and number of those that formed in individual vessels. Our data are consistent with the hypotheses that wound ethylene production is the cause of tylose formation and that embolisms in vessels are not directly required for wound-induced tylosis in pruned grapevines. The possible role of ethylene in the formation of tyloses in response to other stresses and during development, maturation, and senescence is discussed.

The Role of Ethylene in Water-deficit Stress Responses in Betula papyrifera Marsh

One-year-old paper birch (Betula papyrifera Marsh.) seedlings were exposed to water deficit, ethylene, or inhibitors of ethylene action under greenhouse conditions to investigate ethylene's role in water-deficit stress-induced leaf abscission. Exposing well-watered and water-stressed paper birch to 20 ppm ethylene resulted in more than 50% leaf abscission after 96 h regardless of plant water status. However, application of a physiological level (1 ppm) of ethylene did not cause leaf abscission in either well-watered or water-stressed paper birch. Inhibitors of ethylene action (1ppm 1-methylcyclopropene or 0.1 mm silver thiosulfate) did not affect predawn water potential, gas exchange, or chlorophyll fluorescence. A significant increase in ethylene production was not detected in water-stressed paper birch before the onset of significant leaf abscission. Based on these observations, ethylene would appear to play a minor role in water-deficit stress-induced leaf abscission in paper birch.