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1. Details of Module and its Structure
Module Detail Subject Name <BOTANY>
Paper Name <Plant Physiology II>
Module Name/Title <Ethylene>
Module Id <>
Pre-requisites Basic knowledge about Ethylene and its metabolites and their role.
Objectives To make the students aware of ethylene, a phytohormone, that regulates diverse functions in plant.
Keywords Abscission, ACC synthase, cross talk, ethylene, flowering, ripening, S-AdoMet, senescence, signalling, stress response
Development Team
Structure of Module/Syllabus of a module (Define Topic / Sub-topic of module )
<Jasmonate> <Sub-topic Name1>, <Sub-topic Name2>
Role Name Affiliation
Subject Coordinator <Dr.Sujata Bhargava> Savitribai Phule Pune University Paper Coordinator <Dr.Sujata Bhargava>
Content Writer/Author (CW)
<Dr. SirshaMitra> Botany Department, Savitribai Phule Pune University
Content Reviewer (CR) <Dr.Sujata Bhargava>
Language Editor (LE) <Dr. Sujata Bhargava>
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TABLE OF CONTENTS (for textual content) 1. Introduction
2. Ethylene biosynthesis and metabolism 3. Physiological effects
4. Mechanism of gene regulation 5. Cross-talk with other hormones
Introduction
Ethylene is a colorless, flammable and gaseous organic compound with a sweet and musky odor. This is an unsaturated hydrocarbon with carbon-carbon double bond (figure 1). Though ethylene has been used to stimulate the ripening since the ancient Egyptians, the effect of ethylene on the plant growth was noted for the first time in the year 1864 when a leakage of gas from the street lights showed stunning growth, twisting plants, and abnormal thickening in the stem. In 1901, Dimitri Neljubowidentified ethylene as the active compound in the gas responsible for the abnormal growth of the pea seedling. Ethylene is also a naturally occurring plant hormone and influences many plant processes ranging from germination to senescence.
Figure 1: Structure of ethylene
Biosynthesisand Metabolism
In higher plants ethylene is synthesized in all the plant parts namely, roots, tubers, stems, leaves, buds, flowers, and fruits. Ethylene is biosynthesized from methionine via S-adenosyl-L- methionine (S-AdoMet) and 1-aminocyclopropane-1-carboxylic acid (ACC) (figure 2). The
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formation of methionine to Ado-met is catalyzed by the enzyme S-adenosyl-L-methionine
synthetase (SAM synthetase). Nearly, 80% of the cellular methionine is converted to Ado-met. For the synthesis of one molecule of S-AdoMet, one molecule of ATP is required.
Figure 2: Schematic representation of Ethylene biosynthesis. Different steps of JA biosynthesis and enzymes, those are involved in this process[Adapted and modified from Wang et al. (2002)].
Further, S-AdoMet is converted to ACC by the enzyme ACC synthase. This is the rate limiting step in ethylene biosynthesis.Malonylation of ACC to malonyl-ACC (MACC) reduces the ACC pool and hence ethylene production. Along with ACC production, 5’-methyl- thioadenosine (MTA) is also produced as a by-product. Continuous recycling of MTA to methionine allows ethylene
production in a very high rate without high intracellular methionine concentration. The final step of ethylene biosynthesis is catalyzed by the enzyme ACC oxidase which converts ACC to ethylene
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and generates CO2 and cyanide.Toprevent toxicity of accumulated cyanide during high rates of ethylene synthesis, plants detoxified it to cyanoalanine by the enzyme cyanoalanine synthase.
Figure 3: Structure of ethylene metabolites
Earlier, it was believed that ethylene is inert; however, ethylene metabolism was observed in several plant species (Blomstrom and Beyer, 1980). In the cotyledon of Viciafaba, ethylene is rapidly converted to ethylene oxide (Jerie and Hall, 1978) (figure 3).This compound can be readily converted to ethylene-glycol either enzymatically or non-enzymatically (figure 3). Ethylene glycol is a stable end-product of ethylene metabolism. The oxidation of ethylene to ethylene glycol was first observed in pea seedlings (Blomstrom and Beyer, 1980). The enzyme responsible for the conversion of ethylene to ethylene oxide is a monoxygenase. As ethylene oxide showed a synergistic effect with ethylene on induction of the triple response in peas and leaf abscission in cotton, it has been proposed that ethylene oxide can modulate ethylene action. In 1985, Beyer proposed that metabolism of ethylene might be the prerequisite for ethylene action.
Physiological Effects
Ethylene influences plant processes such as seed germination, growth, diageotropism, senescence, flowering, abscission,fruit ripening, abiotic and biotic stress responses.
Seed dormancy and Germination
Seed dormancy prevents germination during the unfavorable period. This allows the seed to survive after being dispersed from the mother plants. The breaking of dormancy is accompanied by several physiological changes that affect subsequent germination response. There are many
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germination stimulating factors namely, gibberellic acid (GA), nitrate, light, chilling, membrane transition etc. It has been shown in many species that ethylene is produced during germination and the production of ethylene is stimulated by the factorsthat break dormancy. Generally, exogenous ethylene stimulates the germination of both dormant and non-dormant seeds; however, in few species ethylene has no effect or adverse effect on germination (Ketring 1977, Kepczynski1985, Esashi 1991, Corbineau and Come 1995).Ethylene can stimulate germination even at very low concentration, ranges from 0.1 to 200 μl L-1. Therefore, in many species inhibited seed germination can be completely or partially reversed by ethylene. Moreover, application of ACC, the immediate precursor of ethylene stimulates the germination in redroot pig weed seeds and
Amaranthuspaniculatus and A. caudatus. The comparison of the effect of ACC and ethylene on seed germination revealed that effect of ethylene is more pronounced than ACC. Together these facts suggested that seeds inability to convert ACC to ethylene is responsible for reduced ethylene production that inhibits seed germination.
Growth, development and senescence
Although each part of plant is capable of ethylene production, it is normally produce in certain developmental stages and in response to specific stimuli. Ethylene inhibits growth by impairing cell division, DNA synthesis and cell expansion in the meristems of roots, shoots and axillary buds. In germinating seedlings, ethylene production is localized in the apical hook region (Goeschi et al. 1967; Taylor et al.1988). Application of ethylene to etiolated seedlings causes three distinct morphological changes (triple response) in the seedling: 1) inhibition of stem elongation 2) radial swelling of the stem 3) absence of normal geotropic response (diageotropism)(figure 4). The major cause for this growth inhibition is ceasation or retardation of mitosis in root and shoot meristem and in axillary buds. In the root apex, ethylene inhibits mitosis by 60%. Ethylene also influences the rate of DNA synthesis. Ethylene reduces the activity of DNA synthase; therefore, DNA synthesis is inhibited within a few hours after ethylene treatment (Burg SP., 1973).
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Figure 4: Effect of ethylene on pea seedlings growth. A. ethylene treated seedlings are showing triple response B. Ethylene treatment reduces radicle growth in pea seedling (Adapted from (A)Neljubow et al., 1901 and (B) Petruzzelli et al., 2003).
Cessation of growth in cells, organs or in the whole plants is termed as Senescence. This process is genetically programmed and controlled by developmental or environmental cues. All major plant hormones are known to be associated with the senescence; however, ethylene was the first plant hormone identified as a senescence accelerator (Neijubow 1901). Genetic and molecular studies of the Arabidopsis mutant unravel the signaling pathway for ethylene mediated triple response(figure 5). In the membrane of endoplasmic reticulum (ER), ethylene is first perceived by its receptor, ETHYLENE RESPONSE 1 (ETR1). Upon ethylene binding, ETR1 is unable to activate a serine/threonine protein kinase, CONSTITUTIVE RESPONSE1 (CTR1); therefore, CTR1 stops phosphorylayion of the protein ETHYLENE INSENSITIVE 2 (EIN2) which is also localized on the ER membrane. Non-phosphorylated cytosolic C-terminal of EIN2 is eventually cleaved by the protease. Further, C-terminus of the cleaved EIN2 is moved into the nucleus where it activates the transcription of different genes (Ju et al., 2012; Qiao et al., 2012; Wen et al., 2012; Ji and Guo, 2013).
A B
No ethylene Ethylene Ethylene No ethylene
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Figure 5: Schematic representation of ethylene signaling. [Adapted from Zhou et al. (1998)]
Flowering, fruit ripening, and abscission
Initiation of flower is an important step in plant’s life. Therefore, plants have evolved mechanisms to regulate flower initiation. Ethylene plays a significant role in flower initiation.
However, it is evident that in some species ethylene inhibits flower induction and enhances flower bud abortion; on the contrary in some species ethylene promotes flower bud induction.In
Arabidopsis ethylene delays flower initiation. Researchers showed that the delay in flower initiation is rescued by loss of function in genes encoding DELLA protein (Achard et al., 2007)(figure 5).
DELLA is regulated by gibberellic acid (GA). Ethylene production inhibits CTR1 and enhances EIN3 levels via the SCFEBF1/EBF2 ubiquitin pathway and activates the ethylene signaling. Activation
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of ethylene signaling reduces the accumulation of bioactive GA and increases the accumulation of DELLA protein. Enhanced DELLA accumulation inhibits the expression of floral meristem identity genes LEAFY (LFY) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1(SOC1) which in turn delay flowering (Achard et al., 2007).
Figure 5: Schematic representation of regulation of flowering by ethylene (Adapted from Achard et al., (2007)
Ethylene stimulates flowering in pineapples, otherbromeliads, mangoes (Halevy 1986) and in some geophytes (Elphinstone and Rees, 1986).
The ripening of fleshy fruits is accompanied by a series of biochemical, physiological and structural changes. Fruits are categorized as climacteric or non-climacteric fruits depending on whether or not a fruit showsthe phenotype of a respiration peak along with an increase in ethylene productionduring ripening. Fruit ripening is a genetically programmed event. A developmentally regulated increase in the expression of both ACO and ACS initiate a rise in the ethylene production.
Fruit softening, one of the ripening processes is very sensitive to ethylene. However, changes in
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fruit color can be ethylene dependent or independent.Several ethylene responsive fruit ripening genes are identified from tomato. Among rapidly induced genes E4 and E8 require very high level of ethylene. Montogomery et al.,(1993) identified an ethylene responsive region in the promoter of E4 gene. Exogenous application of ethylene causes early fruit ripening(figure 6).
Figure 6: Effect of ethylene on fruit ripening. A. Ethylene concentration is increased along with the fruit ripening. B. Treatment with ethylene resulted in early fruit ripening. (Adapted from Pereira et al. 2005;
http://isopaninsulation.com/technologies/fruit-ripening-plants)
Abscission is the process by which plants shed its different parts. This includes leaves, buds, scales, flower, fruits etc. (Sexton et al., 1985). During abscission, active mobilization of cell wall hydrolases weakens the cell wall of the cells in abscission zone and the mechanical force is responsible for shedding of the plant parts. The cells in the abscission zones are typically smaller and less vacuolated and the stele in this zone is not lignified (Sexton 1985).Moreover, during this process, the middle lamella is disappeared and the microfibrils on the primary wall in the abscission zone are swelled and disorganized.Combined activities of several cell wall degrading enzymes are responsible for these changes. Among these enzymes cellulases and pectinases are the major ones.
Ethylene accelerates abscission of leaves, flowers and fruits by regulating the expression of genes of these enzymes.In addition to cellulases and pectinases, some other enzymes namely peroxidases,
3 days after storage at room temperature No ethylene 100 ppm ethylene
Fruit ripening stage 0.0
0.5 1.0 1.5
Ethylene nLg-1h-1
1 2 3 4 5
A B
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uronic acid oxidase, chitinases and β-1, 3glucanase are also associated with the abscission process.Ethylene also enhances the growth of the cells in the abscission zone but not in the neighboring cells. This uneven growth generates the mechanical force. Mechanical force in combination with the weakened cell wall allows the shedding of the plant part (figure 7).
Figure 7: Effect of ethylene on flower abscission. Exposure to ethylene causes early abscission of flowers (Adapted from http://oardc.osu.edu/joneslab/t07pageview/Extension.htm)
Stress response
In response to variety of stresses, plant stimulates ethylene production. For example, ethylene production is enhanced after exposure of plant tissues to low-temperature, water stress, osmotic stress, chemical stress, mechanical stress, gravitational stress, wounding, radiation, ozone and heavy metals, herbivory, and pathogen attack (Wang et al., 1990).Changes in the ethylene production are probably part of the acclimation process that plants develop to cope with the stress conditions. Ethylene induced physiological responses namely, growth inhibition, epinasty, stomatal closure, and senescence and abscission of leaves, flowers, and fruitsmay help plants to maintain normal function and successfully adapt to stressful conditions (Wang et al., 1990).Ethylene also elicits plants defense responses by enhancing the emission of volatile organic compounds, accumulation of phenolics and activity of proteinase inhibitors (Von Dahl and Baldwin,
2007).Ethylene shows a dramatic effect on the expression of plant defense response genes namely, L-phenylalanine ammonia-lyase and 4-coumarate:
No ethylene 1 day 2 days 3 days
Exposure to 2 ppm ethylene
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CoAligase,enzymesofthephenylpropanoidpathway,chalconesynthase,anenzymeoftheflavonoidglyco sidepathway,andhydroxyproline-richglycoprotein,amajorproteincomponentofplantcellwalls. . .Mechanism of gene regulation
Ethylene production increases dramatically during germination, leaf and flower senescence and abscission, and fruit ripening (Yang and Hoffman 1984; Mattoo and Suttle 1991; Abeles et al., 1992). There is a diverse group of stimuli that can affect ethylene biosynthesis. Ethylene itself and also other plant hormones, such as auxin, brassinosteroids, and cytokinin can affect ethylene production (Yang and Hoffman 1984; Mattoo and Suttle 1991; Abeles etal., 1992; Vogel et al., 1998; Woeste et al., 1999). Light (Goeschlet al. 1967; Jiao et al.1987) and a wide variety of stresses such as wounding, pathogen attack, flooding, drought, hypoxia, temperature, physical loads and noxious chemicals such as ozone and sulfur dioxide can induce ethylene production (Yang and Hoffman 1984; Abeles etal., 1992; Bleecker and Kende 2000).
Ethylene production is regulated by differential transcription of ACS gene during the course of development and in response to various external stimuli.In most species, ACS is regulated by multigene families. In tomato, eight genes belongs to ACS family are differentially regulated by various biotic and abiotic factors. Moreover, expressions of different ACS genes are specific to the developmental stages. In tomato fruit, the ripening process is comprised of six different stages;
amongst them ‘Breaker stage’ is the first transition phase where a definite break in color from green to tannish-yellow, pink or red is observed on ~10% of the surface. LE-ACS6is the onlyACSgene expressed in mature green tomato fruit, but it is not expressed afterthe transition to the breaker stage.LE-ACS1A is transiently expressed only during the breaker stage.LE-ACS2andLE- ACS4are the primaryACSgenes expressed after the breaker stage. The steady-state level of RNA expression of LE-ACS2 is highest amongst other ACS genes(Barry et al., 2000)(figure 8).
The use of ethylene insensitive mutant revealed that among all the ACS genes, only LE-ACS2 expression is ethylene dependent.
Figure 8: Expression pattern of ACS genes during fruit ripening.(Adapted from Argueso et al., 2007).
.
In climacteric plants, two systems of ethylene production have been proposed. System I:
According to this system ethylene inhibits its own biosynthesis and takes place during vegetative growth. System II: According to this system ethylene enhances its production (autocatalytic) and takes place during climacteric fruit ripening and senescence of petals in some species (Barry et al 2000; Giovannoni 2001; Alexander and Grierson 2002). LE-ACS1A and LE-ACS6 are responsible for ethylene biosynthesis in green fruit (System I); ethylene biosynthesis in System II is initiated and maintained by the ethylene-dependent expression of LEACS2. In Arabidopsis upon various abiotic stressesethylene biosynthesis is enhanced via increasedtranscription of distinct subsets of ACS genes. Transcript level of ACS6 is increased in response to ozone(Vahalaet al. 1998; Arteca and Arteca 1999).The expression of ACS2, ACS6, ACS7, and ACS9 are elevated duringhypoxia (Peng et al. 2005); however, an anaerobicconditions result in reduced expression of all theACS genes (Tsuchisaka and Theologis,2004). The transcript levels of distinct subsets of ACSgenes increase after wounding and in response toosmotic stress, high temperatures, and droughtconditions (Tsuchisaka and Theologis 2004; Wanget al., 2005).
In addition to ACS transcription, ACS protein turnover also plays an important role in regulation of ethylene biosynthesis. In Arabidopsis, ACS protein is divided into three main groups based on their C-terminal sequences,. Type 1: Proteins consist of an extended C-termini containing three conserved Serine (Ser) residues that are targets for phosphorylation by mitogen-activated protein kinase 6 (MPK6), as well as a conserved Ser residue that is a phosphorylation site for calcium-dependent protein kinase (CDPK) . Type 2: Proteins have shorter C-termini that are targets for only CDPK. Type 3: Proteins consist of a very short C-terminal extension that lacks both the
Figure 9: Model for the regulation of ACS protein. (adapted from Argueso et al., 2007)
phosphorylationsites. It has been found in tomato that stability of ACS activity is varied during fruit ripening. ACS protein is rapidly degraded by 26S proteasome via a C-terminal dependent
mechanism. It has been shown that disruption of ETO1 resulted in increased stability of the ACS5 protein and increased ethylene biosynthesis (Argueso et al., 2007). In Arabidopsis, ETO1 has two paralogs, namely EOL1 and EOL2 which interact with type 2 ACS proteins (Wang et al., 2004).
The ETO/EOL proteins act as adaptors; one end of this protein binds to the ACS protein and the other end binds to aCUL3/E3ligase. Binding of ETO 1 catalyzes the addition ofubiquitin moieties on the ACS substrate. Then the substrate is ubiquitinated by the ligase and targeting theprotein for degradation by the 26S proteasome.The stability of ACC is dependent on the phosphorylation of the protein.Phosphorylation of ACS proteins blocks thebinding of ETO1/EOL proteins to ACS, thus inhibiting the ubiquitination of these ACS proteins and their degradation by the 26S proteasome (figure 9).
.
.Cross talk
Ethylene is controlling several aspects of plant growth and development; in addition it is also interacting with other plant hormones namely auxin, gibberellin, jasmonic acid (JA), salicylic acid (SA).
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Ethylene and auxin
Ethylene production is enhanced by exogenous application of auxins (Yu and Yang, 1979;
Woeste et al., 1999). In Arabidopsis,tomato, and lupinauxin upregulates the expression of ACC synthase and induces ethylene biosynthesis(Abel et al.,1995; Abel and Theologis, 1996), whereas in mung bean it enhances the expression of both ACCsynthase and ACCoxidase (Yu et al., 1998). In Arabidopsis, transcription of eight out of the nine ACS genes is upregulated by auxin. Promoters of several of ACS genes possess canonical auxin response elements in them (Tsuchisaka and
Theologis, 2004).It has been shown in Arabidopsis that auxin regulates the expressionof ACC synthase 4 (ACS4) via modulating the expression of AXR1- and AXR2 (Abel et al., 1995(figure 10).AXR1, an auxin-resistance gene encodes a protein related to ubiquitin activating enzyme E1.
Figure 10. Schematic representation of crosstalk between ethylene and auxin (Adapted from Swarup et al. 2002).
On the other hand, ethylene regulates auxin level and auxin transport (Morgan and Gausman, 1966).
Ethylene mediated upregulation of HOOKLESSI gene expression that facilitates apical hook formation is achieved by modulating the levels or transport of auxin (Kieber, 1997).
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Ethylene and gibberellin
The complex interaction between ethylene and GA demonstrated both negative and positive reciprocal effect. The mode of interaction between ethylene and JA is determined by the
developmental and environmental circumstances. Antagonistic interaction between ethylene and GA inhibits growth in Arabidopsis (Achard et al., 2003). The inhibitory effect ofethylene on plant growth and the interaction with GA is mediated by the DELLA proteins. On the contrary, GA promotes ethylene responses namely, apical hook formation in the dark and hypocotyl elongation in the light-grown seedling (figure 11).
Figure 11. Schematic representation of crosstalk between ethylene and GA (Adapted from Weiss et al., 2007)
In oxygen deficient condition, GA positively influences ethylene activity. The elongation ofinternodes in deepwater-rice requires synergistic effect of GAand ethylene (Sauter et al., 1995). In submerged condition, reduced O2 levelinduces ethylene production. Increased ethylene level
inhibits ABA synthesis.It is evident in Rumexpalustris that submergence induces the expression of GA3ox gene which encodes the enzyme responsible for the production of active GA. Therefore, during submergence in one hand ethylene reduces ABA synthesis and on the other hand enhances
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GA accumulation. The change in the balance between ABAand GA, results in a GA-induced stem elongation (figure 11).
Ethylene and JA and SA
Most of the studies showed that ethylene and JA signaling pathway interact
synergistically.Both ethylene and JA signaling are required for the expression of defense related genes.
Figure 12: Schematic representation of the proposed function of ERF1 and MYC2 in ethyele- JA cross-talk.(Adapted from http://genesdev.cshlp.org/content/18/13/1577/F7.expansion.html)
Moreover, they often function in parallel and regulate same plant responses. Transcription factors namely, MYC2, ETHYLENE RESPONSE FACTOR1 (ERF1), and JAZ proteins play an important role in the regulation of this synergy (Anderson et al., 2004; Lorenzo et al., 2004). MYC2
dependent genes are activated synergistically by JA. However, MYC2 is responsible for the
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repression of ethylene/JA induced gene expression. Expressions of ERF-1 dependent genes are regulated by the combined action of ethylene and JA (figure 12).
Figure 13.Schematic representation of crosstalk between ethylene and JA and SA (Adapted from Kazan and Manners 2012).
After an attack by herbivore or a necrotrophic pathogen, both ethylene and JA are increased.
Elevated JA rapidly conjugated with isoleucine (Ile) and binds toCoronatine insensitive-1 (COI1) and facilitates COI-1dependent degradation of JAZ repressor protein. This releases the repression exerted on EIN3 and EIL1. EIN3 and EIL1 from both JA and ET pathways and activates JA- and ET-responsive defense genessuch as plant defensing 1.2 (PDF1.2).Ethylene negatively regulates SA signaling. As mentioned earlier, after release of the repressor from EIN3 and EIL1, they bind to the
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promoter of the SA biosynthesis gene SID2 and repress its expression and subsequently impairs SA biosynthesis and expressionof pathogenesis related protein1 (PR1) (figure 13).
References
1. Abel S and Theologis, A (1995) A polymorphic bipartite motif signals nuclear targeting of early auxin-inducible proteins related to Ps-IAA4 from pea (Pisumsativum).Plant J 8: 87-96.
2. Abel S, Theologis A (1996) Early gene and auxin action. Plant Physiolll: 9-17.
3. Abeles FB, Morgan PW, Saltveit ME Jr (1992) Ethylene in Plant Biology San Diego, CA, USA: Academic Press, Inc.
4. Achard P, Baghour M, Chapple A, Hedden P, Straeten D, Genschik P,Arteca J, Arteca R (1999) A multi-responsive gene encoding 1-aminocyclopropane-1-carboxylate synthase (ACS6) in mature Arabidopsis leaves. Plant MolBiol 39:209–219.
5. Achard P, Vriezen WH, Van Der Straeten D, Harberd NP (2003) Ethylene regulates Arabidopsis development via the modulation of della proteingrowth repressor function.
Plant Cell 15: 2816–2825.
6. Anderson JP, Badruzsaufari E, Schenk PM, Manners JM, Desmond OJ, Ehlert C, Maclean DJ, Ebert PR, Kazan K(2004) Antagonistic interaction between abscisic acid and jasmonate- ethylene signaling pathways modulates defense gene expression and disease resistance in Arabidopsis. Plant Cell 16: 3460–3479.
7. Argueso CT, Hansen M, Kieber JJ (2007) Regulation of Ethylene Biosynthesis. J Plant Growth Regul. 26:92–105.
8. Barry CS, Llop-Tous MI, Grierson D (2000)The regulation of 1 aminocyclopropane-1- carboxylic acid synthase gene expression during the transition from system-1 to system-2 ethylene synthesis in tomato. Plant Physiol 123:979–986
9. Brown KM (1997) Ethylene and abscission. Physiol Plant 100: 567-576.
10. Bleecker AB, Kende H (2000) Ethylene: a gaseous signal molecule in plants.Annu Rev Cell Dev Biol 16:1–18.
11. BlomstromDC , Beyer EM Jr (1980) Plants metabolise ethylene to ethylene glycol.Nature 283:66 – 68.
12. Burg SP (1973) Ethylene in Plant Growth.Proc Nat AcadSci USA 70 (2): 591-597
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13. Elphinstone E D, Rees AR (1985) Forcing out the Dutch to flower all year round in the UK Grower 33-39.
14. Esashi Y (1991) Ethylene and seed germination: The Plant Hormone Ethylene (A K Mattoo and JCSuttle, eds) CRC Press, Boca Raton, FL. 133-157.
15. Giovannoni J (2001) Molecular biology of fruit maturation and ripening.Annu Rev Plant Physiol Plant MolBiol 52:725–749.
16. Goeschl JD, Pratt HK, Bonner BA (1967) An effect of light on the production of ethylene and the growth of the plumular portion of etiolated pea seedlings. Plant Physiol 42:1077–
1080.
17. Halevy AH (1986) Recent advances in the use of growth substances in ornamental
horticulture Plant growth substances M Bopp (eds) Springrer-Verlag Berlin Heidelberg 391- 398.
18. Jaffe MJ, Telewski FW(1984) Thigmomorphogenesis: callose and ethylene in the hardening of mechanically stressed plants In phytochemical adaptations to stress Timmerman BN et al.
(eds):79-92
19. Jerie PH, Hall MA (1978) The Identification of Ethylene Oxide as a Major Metabolite of Ethylene in Viciafaba L. Proc Royal Soc B 200:1138.
20. Ji Y, and Guo H (2013) From endoplasmic reticulum (ER) to nucleus: EIN2 bridges the gap in ethylene signaling.Mol Plant 6: 11–14.
21. Jiao X, Yip WK, Yang SF (1987) The effect of light and phytochrome on 1-
aminocyclopropane-1-carboxylic acid metabolism in etiolated wheat seedling leaves. Plant Physiol 85:643–647.
22. Ju C, Yoon GM, Shemansky JM, Lin DY, Ying ZI, Chang J et al. (2012) CTR1
phosphorylates the central regulator EIN2 to control ethylene hormone signaling from the ER membrane to the nucleus in Arabidopsis.ProcNatlAcadSci USA 109: 19486–19491.
23. KazanK , MannersJM ( 2012) JAZ repressors and the orchestration of phytohormone crosstalk.Trends Plant Sci.17(1): 22–31
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24. Ketring DL (1977) Ethylene and seed germination Physiology and Biochemistry of Seed Dormancy and Germination (KhanAA eds). North Holland Publishing Co, Amsterdam 157- 178.
25. Kgpczynski J,K^pczyriska E (1997) Ethylene in seed dormancy and germination.Physiol Plant 101:120-126
26. Kgpczynski J (1985) The role of ethylene in seed germination.ActaHortic 167:47-55 27. Kieber JJ (1997) The ethylene response pathway in Arabidopsis.AnnuRev Plant Physiol
Plant MolBiol48:277–96.
28. Kim J, Chang C, Tucker ML (2015)To grow old: regulatory role of ethylene and jasmonic acid in senescence Front Plant Sci6:20.
29. Lelievre JM, Latche A, Jones B, Bouzayen M, Pech JC (1997) Ethyleneand fruit ripening.
Physiol Plant 101: 727-739.
30. Lorenzo O, Piqueras R, Sánchez-Serrano JJ, Solano R(2003) ETHYLENE RESPONSE FACTOR1 integrates signals from ethylene and jasmonate pathways in plant defense. Plant Cell 15:165–178.
31. Mattoo AK, Suttle JC (1991)The plant hormone ethylene. Boca Raton, FL, USA: CRC Press.
32. Montgomery J, Goldman S , DeikmanJ , MargossianL , Fischer RL (1993) Identification of an ethylene-responsive region in the promoter of a fruit ripening gene.
ProcNatlAcadSciUSA 90: 5939-5943.
33. Morgan PW, Gausman HW(1966) Effects of Ethylene on Auxin Transport Plant Physiol 41, 45-52
34. Morgan PW, Drew MC (1997) Ethylene and plant responses to stress.Physiol Plant 100:
620-530.
35. Moritz T, HarberdNP( 2007) The plant stress hormone ethylene controls floral transition via DELLA-dependent regulation of floral meristem-identity genes. ProcNatlAcadSci USA 104(15).
36. Neljubow D (1901) Ueber die horizontale Nutation der Stengel von Pisum sativum und einiger anderer Pflanzen. Beih Bot Zentralbl 10, 128-139.
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37. Peng HP, Lin TY, Wang NN, Shih MC (2005) Differential expression of genes encoding 1- aminocyclopropane-1-carboxylate synthase in Arabidopsis during hypoxia. Plant MolBiol 58:15–25.
38. Pereira F L P, Galvão RM, Kobayashi AK, Cação S M B, Vieira L G E (2005) Ethylene production and acc oxidase gene expression during fruit ripening ofCoffeaarabica L.Braz J Plant Physiol 17 (3): 283-289.
39. Petruzzelli L, Sturaro M, Mainieri D, Leubner-Metzger G (2003)Calcium requirement for ethylene-dependent responses involving 1-aminocyclopropane-1-carboxylic acid oxidase in radicle tissues of germinated pea seeds. Plant Cell and Environ 26: 661-671.
40. Qiao, H, Shen, Z, Huang, S S, Schmitz, R J, Urich, M A, Briggs, S P, et al. (2012) Processing and subcellular trafficking of ER-tethered EIN2 control response to ethylene gas.Science 338: 390–393.
41. Sauter M, Mekhedov SL, Kende H (1995) Gibberellin promotes histone H1 kinase-activity and the expression of CDC2 and cyclin genes during the induction of rapid growth in deep- water rice internodes. Plant J 7:623–632.
42. Sexton R Lev^'is L N,,Trewava S A J Kelly P (1985) Elhylene and abscission: InEthylene and Plant Development (J A Roberts and G A, Tucker ( eds) Butterworths London 173-196.
43. Swarup R, Parry G, Graham N, Allen T and Bennett M (2002) Auxin cross-talk: integration of signalling pathways to control plant development.Plant MolBiol49: 411-426.
44. Taylor, JE, Grosskopf, DG, McGaw, BA, Horgan, R, and Scott, IM (1988) Apical
localization of 1 -aminocyclopropane- 1-carboxylic acid and its conversion to ethylene in etiolated pea seedlings. Planta 174, 112-114.
45. Tsuchisaka A, Theologis A (2004) Unique and overlapping expression patterns among the Arabidopsis 1-amino-cyclopropane- 1-carboxylate synthase gene family members. Plant Physiol 136:2982–3000.
46. Vogel JP, Schuerman P, Woeste KW, Brandstatter I, Kieber JJ (1998) Isolation and characterization of Arabidopsis mutants defective in induction of ethylene biosynthesis by cytokinin. Genetics 149:417–427.
47. Vahala J, Schlagnhaufer CD, Pell EJ (1998) Induction of an ACC synthase cDNA by ozone in light-grown Arabidopsis thaliana leaves.Physiol Plant 103:45–50.
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48. Von Dahl C C, Baldwin, I T (2007) Deciphering the role of ethylene in plant-herbivore interactions. J Plant Growth Regul26(2): 201-209.
49. Wang KLC, Li H, Ecker JR (2002) Ethylene Biosynthesis and Signaling Networks. Plant Cell S131- 151.
50. Wang SY, Wang CY, Wellburn AR (1990) Stress responses in plants: adaptation and acclimation mechanisms: Role of ethylene under stress conditions. Publisher Wiley- Liss New York, NY.
51. Wen X, Zhang C, Ji Y, Zhao Q, He W, An F, et al. (2012) Activation of ethylene signaling is mediated by nuclear translocation of the cleaved EIN2 carboxyl terminus.Cell Res 22:
1613–1616.
52. Woeste K, Ye C, Kieber JJ (1999) Two Arabidopsis mutants that overproduce ethylene are affected in the post-transcriptional regulation of ACC synthase. Plant Physiol 119:521–530.
53. Yang SF, Hoffman NE (1984) Ethylene biosynthesis and its regulation in higher plants.Annu Rev Plant Physiol 35:155–189.
54. Zhou L, JangJ, JonesTL, and SheenJ (1998) Glucose and ethylene signal transduction crosstalk revealed by an Arabidopsis glucose-insensitive mutant.ProcNatlAcadSci USA 95:10294 –10299.
55. Wang N, Shih M, Li N(2005) The GUS reporter-aided analysis of the promoter activities of Arabidopsis ACC synthase genes At-ACS4, AtACS5, and AtACS7 induced by hormones and stresses. J Exp Bot 56:909–920.
56. Weiss D, Ori N(2007) Mechanisms of Cross Talk between Gibberellin and other hormones.
Plant Physiol 144: 1240–1246.
57. Yu S, Kim S, Lee JS and Lee, DH (1998) Differential accumulation of transcripts for ACC synthase and ACC oxidase homologs in etiolated mung bean hypocotyls in response to various stimuli. Mol Cells 8: 350-358.
