Biosynthesis, translocation, physiological role in cell level, basic functions and mechanism of action of Ethylene

1. ETHYLENE
J.PREETHI FETRICIA
I Ph.D. HORTICULTURE

2. INTRODUCTION
 Ethylene (C2H4) is a simple gaseous hydrocarbon that has profound effects upon
plant growth and development (reviewed in Mattoo and Suttle, 1991; Abeles et al.,
1992).
 Ethylene is released easily from the tissue and diffuses in the gas phase through the
intercellular spaces and outside the tissue.

3. CONT….
 Its molecular weight
is 28
 Lighter than air
under physiological
conditions
 Highly inflammable
 Redily undergoes
oxidation
 Ethylene can be
oxidized to ethylene
oxide
 Ethylene oxide can
be hydrolyzed to
ethylene glycol

4. DISCOVERY
Ethylene was one of the plant hormones discovered which is produced by all cells
during plant development, but rates vary, with the highest rates being associated
with meristematic, stressed, or ripening tissues
Illuminating gas produced from coal
Leaks from pipelines
Resulted in premature senescence
and abscission in nearby vegetation
seriously damaging trees and
greenhouse plants
In nineteenth and early twentieth centuries
(Abeles et al., 1992).
Identified the active component in
illuminating gas as ethylene
1910 - H. H. Cousins
Identified ethylene chemically as a
natural product of plant metabolism.
1901 - Dimitry Neljubov
First indication that ethylene is a
natural product of plant tissues
1934 - Gane et al.,

5. Illuminating gas Triple response

6. ETHYLENE MEASUREMENT
 Measurement of ethylene in plants is a critical step in understanding the
underlying mechanisms by which ethylene regulates the physiological and
developmental processes of plants.
 Gas chromatography is a common analytical technique for analyzing
compounds that are in vapor form or can be vaporized at an appropriate
temperature .
 Due to its versatility, efficiency, and sensitivity, gas chromatography has
become instrumental for measuring ethylene produced by plants

7. Overlay of chromatograms of
entrenched ethylene in
commercially available
industrial solvents.
Overlay of chromatograms of
ethylene in air from three
different locations.
Bae lee et al., 2020

8. BACTERIA, FUNGI, AND PLANT ORGANS
PRODUCE ETHYLENE
 Ethylene production highest in senescing tissues and ripening fruits (>1.0 nL
g per fresh weight/ h), Ethylene concentration in a ripe apple 2500 μL/L.
 In bean (Phaseolus vulgaris),young leaves produce 0.4 nL/ g/h, compared
with 0.04 nL/ g/ h for older leaves.
 With few exceptions, nonsenescent tissues that are wounded or
mechanically perturbed will temporarily increase their ethylene production
severalfold within 30 minutes.
 Gymnosperms and lower plants, including ferns,mosses, liverworts, and
certain cyanobacteria, all have ability to produce ethylene.
 Fungi and bacteria contributes significantly to the ethylene content of soil
 Enteric bacterium Escherichia coli and of yeast (a fungus) produce large
amounts of ethylene from methionine
 Recently both a marine sponge and cultured mammalian cells can respond to
ethylene, raising the possibility that this gaseous molecule acts as a signaling
molecule in animal cells (Perovic et al. 2001).

9. TRANSPORT OF ETHYLENE
 Transported as gas
 Diffuse through the air space
 Transport in cytosol
 Travels from cell to cell through symplast and
pholem
 During flooding conditions, transport of ACC
through xylem sap from root to shoot.

10. EFFECTS OF ETYLENE ON PLANT DEVELOPMENT. (+)
STIMULUS; (-) INHIBITION (FROM AYUB, 1995).

11. BIOSYNTHESIS
The enzymatic steps of the ethylene biosynthetic pathway were
uncovered in fruit; subsequent work in fruit and in dark-grown
Arabidopsis seedlings identified a conserved biosynthetic pathway
and revealed important regulatory mechanisms that control pathway
activity (Adams and Yang, 1979; Yang and Hoffman, 1984;
Booker and DeLong, 2015; Yoon, 2015).
The pathway has only two committed steps:
 Conversion of S-adenosyl-l-methionine (SAM) to 1-
aminocyclopropane-1-carboxylic acid (ACC) by ACC synthase
(ACS),
 Conversion of ACC to ethylene by ACC oxidase (ACO)
(Houben and Van de Poel, 2019).

13. MECHANISM AND CELLULAR SIGNALLING
 It involves three steps
 Binding of ethylene to a receptor
 Activation of one or more signal transduction
pathways
 Modulation of gene expression leading to
ethylene response

14. ETHYLENE BINDING SITE
(A) Copper loading of ethylene receptors
by RAN1. RAN1 is a copper transporting
ATPase. Copper is bound to RAN1 by two
amino terminal metal-binding motifs and
then transported across the membrane.
Copper is delivered to the ethylene receptor
apoproteins. One copper ion is coordinated
per receptor homo-dimer. Upon
coordinating copper, the ethylene receptors
are competent for ethylene binding.
(B) Transmembrane structure of
ethylene binding site. There is one copper
binding site and consequently one ethylene
binding site per receptor homodimer.
(Hirayama et al., 1999; Woeste and
Kieber,2000).

15. Chapter 22
Taiz plant physiology 3rd
ed.

17. Bakshi,et al., (2015)

18. PHYSIOLOGICAL ROLE OF ETHYLENE
 Fruit Ripening
 Plumular Hook formation
 Triple response
 Root and root hair formation
 Leaf epinasty
 Sex expression
 Flowering
 Senescence
 Abscission of leaves
 Breaking of seed and bud dormancy
V.K JAIN (2015)

19. FRUIT RIPENING
 Ripening is the process by which fruits attain their desirable
flavor, quality, color, palatable nature and other textural properties.
 Ripening is associated with change in composition i.e.
i. Conversion of starch to sugar.
ii. Change in colour
iii. Change in firmness
iv. Shape and size
v. Odour /smell
ENZYME
ACTIVITY

21. Iqbal et al., 2017

22. ENZYMATIC ACTION

23. EXAMPLES

25. RESPIRATION AND CO2 EMISSION IN RIPENING

26. CASE STUDY

27. CONTI….

28. PLUMULAR HOOK FORMATION
Activation of HLS1 by Mechanical Stress via Ethylene-Stabilized
EIN3 Is Crucial for Seedling Soil Emergence
 HOOKLESS 1 (HLS1), a critical gene in apical hook formation in
Arabidopsis thaliana, is required for seedling emergence from the soil.
 When grown under soil, hls1 mutant exhibits severe emergence defects.
 By contrast, HLS1 overexpression in the hls1 background fully restores
emergence defects and displays better emergence capacity than that of WT.
 RESULT
 Results indicate that HLS1 transcription is stimulated in response to the
mechanical stress of soil cover, which is dependent on the function of the
transcription factors ETHYLENE INSENSITIVE 3 (EIN3) and EIN3-
LIKE 1 (EIL1). Soil-conferred mechanical stress activates the ethylene
signaling pathway to stabilize EIN3 by repressing the activity of the F-box
proteins EBF1 and EBF2.
Xing Shen et al.(2016)

29. Xing Shen et al.(2016)

30. TRIPLE RESPONSE
 The triple response can be induced in
Arabidopsis seedlings by application of
ACC
 Triple response in Arabidopsis seedlings is
characterized by a
 shortened and thickened hypocotyl,
 an inhibition of root
 elongation, and
 the formation of an exaggerated apical
hook (Guzmán and Ecker, 1990).
 These features contrast sharply with the
etiolated phenotype observed in dark
grown seedlings exposed to air.

31. THE TRIPLE-RESPONSE TO ETHYLENE OF DARK-
GROWN ARABIDOPSIS SEEDLINGS
(B) Wild-type seedling grown in the presence of the ethylene precursor ACC.
(C) Close-up of the pronounced apical hook found with the triple response to ethylene.
(D) Close-up of the shortened root found with the triple response to ethylene.
Eric Schallera et al., 2014
Aradiopsis book
(A) Wild-type
seedlings grown in
the absence (left) or
presence(right) of
ethylene

32. CASE STUDY

33. CONTI….

34. FORMATION OF ADVENTITIOUS ROOT AND ROOT HAIRS
Ethylene is capable of inducing
adventitious root formation in leaves,
stems, flower stems, and even other roots.
Ethylene has also been shown to act as a
positive regulator of root hair formation in
several species .This relationship has been
best studied in Arabidopsis, (Dolan et al.
1994).
Seedlings grown in the presence of
ethylene-treated roots, extra root hairs
forms,
Seedlings grown in the presence of
ethylene inhibitors (such as Ag+), as well
as ethylene-insensitive mutants, display a
reduction in root hair formation

35. CASE STUDY

36. CASE STUDY
Figure 1. A, Thirty-five-day-old
mutant NR and wild-type tomato
plants. Whole-plant root
morphologies are not visually
distinguishable. B, Seventy-seven-
day-old mutant NR tomato stems
with reduced adventitious root
formation compared with wild-type
stems. C, Response of 7-d-old
mutant NR and wild-type seedlings
germinated and grown on sand.
Approximately one-half of NR
seedlings grew horizontally and
had longer taproots and shorter
hypocotyls than wild-type seedlings
(denoted by arrows). D, Reduced
adventitious root formation in
mutant NR vegetative cuttings
compared with wild-type cuttings.
Stem cuttings were propagated for
21 d. E, Reduced adventitious root
formation in transgenic 44568
petunia vegetative cuttings
compared with wild-type cuttings.
Stem cuttings were propagated for
21 d.

37. LEAF EPINASTY
 The downward curvature of leaves that occurs when the upper
(adaxial) side of the petiole grows faster than the lower (abaxial) side
is termed epinasty.
 Ethylene and high concentrations of auxin induce epinasty,
 It has now been established that auxin acts indirectly by inducing
ethylene production.
Control Ethylene

39. ETHYLENE FLUXES IN FLOODED PLANTS

40. CASE STUDY

41. CONTI….
 The effect of short periods of ethylene treatment on epinasty is
shown in Table III. The data indicate that one or more hours of
ethylene treatment were sufficient to cause epinasty. The
curvature of petioles was the same as that shown when they
were re-examined 24 hr later.

42. CONTI….
 Greater curvature was
observed when explants
were treated with ethylene in
the presence of auxin.
Figure 4 shows that a 24-hr
exposure to 10 pill ethylene
increased petiole curvature
by 200. Application of IAA to
various parts of the explant
resulted in even greater
curvature and the maximum
effect was observed when
the auxin was applied so that
it would reach the upper side
of the petiole.

43. SEX EXPRESSION
 On plants that have separate male and female flowers
(monoecious species), ethylene may change the sex of
developing flowers.
 In cucumber (Cucumis sativus), exogenous application of
ethylene increases femaleness, and gynoecious genotypes
(those that produce female flowers only) were reported to
produce more ethylene (Iwahori et al., 1970).
 Two ACS genes, CsACS2 and CsACS1G, were correlated
with female flower production (Trebitsh et al., 1997;
Yamasaki et al., 2001).
 Kamachi et al. (1997) reported that both the timing and the
levels of expression of the CsACS2 transcript were correlated
with the development of female flowers.

44. FLOWERING
 Although ethylene inhibits flowering in many
species, it induces flowering in pineapple and its
relatives, and it is used commercially in pineapple
for synchronization of fruit set.
 Flowering of other species, such as mango, is
also initiated by ethylene.

45. CASE STUDY

46. EFFECT OF CULTIVATION TEMPERATURE ON SEXUAL EXPRESSION AND
FEMALE FLOWER DEVELOPMENT
 Fig. 1 shows the sexual expression of the main and lateral shoots of the
triploid seedless cv. Fashion, and the diploid cv. Premium under standard
greenhouse conditions in Almería (Spain). Both cultivars were grafted onto
the Cucurbita rootstock Ercole. Under standard environmental conditions the
two cultivars behaved as monoecious, producing both male and female
flowers in the same plant. However, when grown at elevated temperatures,
some of the female flowers were converted into bisexual ones, developing a
variable number of immature stamens, although some stamens reached
maturity and produced pollen

47. CONTI….

48. CONTI….
 Effects of external treatments with ethephon and AVG
on sexual expression and flower development

49. Ethylene production among the different flower
organs (Trivellini et al., 2011a,b)
Representative flowers in bud
(B), open (OF) and
senescent (SF) flower
stages.
Ethylene changes in different
flower organs,
petal (pink line bar), style-
stigma plus stamens (S-
S+S; orange line bar) and
ovary (yellow line bar).

50. SENESCENCE AND ABSCISSION OF LEAVES
 Exogenous applications of ethylene or ACC (the precursor of ethylene)
accelerate leaf senescence, and treatment with exogenous cytokinins
delays leaf senescence
 Enhanced ethylene production is associated with chlorophyll loss and
color fading, which are characteristic features of leaf and flower
senescence
 Consistent with a role for ethylene in leaf senescence, both etr1 and
ein2 were found to be affected not only during the early stages of
germination, but throughout the life cycle, including senescence
(Zacarias and Reid 1990;Hensel et al. 1993; Grbiˇc and Bleecker
1995).
 The ethylene mutants retained their chlorophyll and other chloroplast
components for a longer period of time compared to the wild type.
 However, because the total life spans of these mutants were increased
by only 30% over that of the wild type, ethylene appears to increase
the rate of senescence

51. Effect of ethylene on abscission in birch (Betula pendula). The plant on the left is the
wild type; the plant on the right was transformed with a mutated version of the
Arabidopsis ethylene receptor, ETR1-1.
Effect of ethylene in leaf abcission of
ethylene
W ETR1 -
mutant
Untreated Ethylene

52. ABSCISSION OF LEAVES

53. CASE STUDY

54. CONTI….
FI G. 2. Development
of Nicotiana sylvestris
plants: wild type, WT
(A); Pro35S:ETR1-1 R8
(B); and
Pro35S:LeEIL1 e13 (C)
and e17 (D). Plants
were photographed at
10 d before flowering

55. CONTI….

56. CONTI….

57. BREAKING OF SEED AND BUD DORMANCY
Interactions between ethylene, abscisic acid, and nitric oxide signaling
pathways in the regulation of seed germination and dormancy.
 Ethylene positively regulates its ownbiosynthesis,byacting on ACC
synthesis catalyzed by ACS and subsequent conversion to ethylene by
ACO.
 Ethylene is perceived by receptors (amongwhichETR1) located in the
endoplasmic reticulum;its binding leads to the deactivation of the
receptors that become enable to recruit CTR1.
 Release of CTR1 inhibition allows EIN2 to actas a positive regulator of
ethylene signaling pathway.
 EIN2 acts upstream of nuclear transcription factors, such as EIN3,
EILs, and ERBPs/ERFs.
 Ethylene down regulates ABA accumulation by both inhibiting its
synthesis and promoting its inactivation, and also negatively
regulates ABA signaling
Erwann Arc et al., 2013

59. Dual effects of ethylene on potato dormancy and
sprout growth
 Dormant potato tubers (Solanum tuberosum L.) of two
cultivars were treated with various concentrations of
ethylene gas for various exposure periods.
 As has been shown by others, ethylene caused a rapid
but transient increase in respiration rate, which appeared
to be independent of any effects on dormancy.
 All concentrations tested caused accelerated sprouting, 2
microliters per liter being the most effective.
 Ethylene exerts a dual effect on potato tubers: it
markedly shortens the duration of rest, but it inhibits
elongation of the sprouts during extended treatment
IRENA et al., 1974

61. CASE STUDY

62. CONTI….

63. CASE STUDY

66. REFERENCE
 Lee J-B, Jeong YA, Ahn DJ, Bang IS. SPME-GC/MS Analysis of Methanol in
Biospecimen by Derivatization with Pyran Compound. Molecules. 2020; 25(1):41.
https://doi.org/10.3390/molecules25010041