Plants have evolved various defense responses to insect herbivore attack. They can recognize herbivore feeding and oviposition through compounds in oral secretions and eggs. This triggers early signaling events like membrane depolarization, calcium signaling, and reactive oxygen species production. Mitogen-activated protein kinase cascades then activate jasmonic acid pathways to regulate the expression of direct and indirect defense genes. Direct defenses include production of toxic specialized compounds, hypersensitive response, reduced digestibility through proteinase inhibitors, and reallocation of resources away from the herbivore. Indirect defenses attract predators and parasitoids through herbivore-induced plant volatiles and extrafloral nectar secretions. Together, these complex signaling

1. Welcome
1

2. PLANT DEFENSE RESPONSES TO HERBIVORE
INSECTS
H S GADAD
PGS13AGR5965
2
Doctoral seminar-iii

3. OutlineOutline
• Introduction
• Recognition of Insect Herbivore Attack
• Early Events in the Plant defense
• Regulation of Defense Responses
• Types defense Responses
• Conclusion
3

4. Introduction
4

5. Recognition of Insect Herbivore Attack
• Plants have the ability to distinguish between
herbivory and mechanical damage, such as hail and
wind, as well as to recognize ovipositioning
• This feature is needed to avoid wasting expensive
defense resources, since production and release of
defense responses only benefits herbivore-
challenged plants
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6. 6

7. Insect Oral Secretions
• Plants are able to recognize compounds in insect
oral secretions, which elicit more intense defense
responses
• Compared with the vast diversity of herbivores
that attack plants, very few herbivore-derived
elicitors are known
• Conjugation of plant- and herbivore-derived
precursors result in the formation of fatty acid-
amino acid conjugates (FACs)
7

8. Herbivore-associated elicitors
8
Bonaventure et al., 2011

9. Oviposition Fluids
• Insect oviposition fluids can give rise to defense
responses in the plant
• Many female adult herbivorous insects lay eggs
directly into plants, and some species are known
to perceive insects’ oviposition activities and
deploy defenses responses
9

10. Oviposition-induced plant responses acting against the herbivores
10

11. Hilker and Meiners, 2006
11
Cont…

12. Early Events in the Plant defense
• Successful implementation of an induced
defense response requires that plants respond
to herbivory both rapidly and accurately
• Early signaling events at the plant-insect
interface, which occur well before changes in
host plant gene expression and defense-
related metabolism
12

13. Events in plants after feeding by insect herbivores
13

14. Membrane potential changes
• The plant plasma membrane is in direct contact
with the environment, and is therefore able to
recognize outer changes and initiate cascade
events leading to a possible defense response
• Herbivore feeding will lead to an immediate
change in the cell membrane potential (Vm), or
modulate the ion flux at the plasma membrane
level
• The Vm changes induced by herbivory are
followed by a fast electric signal (action
potential), which travels through the entire plant
from the point where the signal was induced 14

15. Ca2+ Homeostasis
• Calcium ions function as a second messenger in
several plant signaling pathways
• In healthy cells, the cytosolic Ca2+
concentration is lower than in the apoplastic
fluid, and cellular organelles
• This creates a driving force for the influx of
Ca2+ into the cytosol, via channel proteins
where it acts as a messenger to induce defense
related signals
15

16. Reactive Oxygen Species
• Superoxide anion, hydrogen peroxide, singlet,
and hydroxyl radical are collectively called
ROS
• They are produced in mitochondria,
chloroplasts, and peroxisomes, as well as on
the external surfaces of plasma membranes
16

17. Calcium variations in Maidenhair tree upon mechanical
damage and herbivore wounding
Mohanta et al., 2012
17

18. H2O2 variations in Maidenhair tree upon mechanical
damage and herbivore wounding
18

19. MAPK Signaling
• Mitogen-activated protein kinase (MAPK)
cascades are important pathways for
downstream sensors and receptors that
regulate cellular responses to insect attack
• MAPK signalling induces the biosynthesis of
jasmonic acid
19

20. Tomato MAPKs function in the systemin-mediated defense response
against herbivorous insects
Kandoth et al., 2007
20

21. Systemic Signaling
• In plants attacked by insect herbivores, the
expression of several defense genes is induced in
undamaged leaves
• Several components have been identified that are
involved in the systemic induction of defense
responses
• Systemin peptides
• Oligogalacturonides (OGAs)
• Jasmonates 21

22. 22

23. Regulation of Defense Responses
Levels of jasmonic acid rise in response
to herbivor damage
This hormone can trigger many types of plant
defenses including bioactive compounds
The action of jasmonic acid induces the
transcription of many genes involved in plant
defense
Jasmonic acid turns on genes for proteinase
inhibitor. 23

24. Model of jasmonate regulation of defense
responsive genes
Lee et al., 2010
24
a) Resting stage b) Response to herbivore wounding

25. 25
(c) In the presence of (+)-7-epi-JA-L-Ile and the absence of
gibberellic acids
(d) If GAs are present, they will bind to DELLA and trigger degradation

26. Types of Defense Responses
26

27. Direct Defense Response
The term “direct defense” is used when
plants produce physical barriers against
insect herbivores, or compounds that exert
repellent, antinutritive or toxic effects on the
herbivores themselves
• Bioactive Specialized Compounds
• Hypersensitive response
• Digestibility Reduction
• Reallocation of Resources
27

28. Bioactive Specialized Compounds
• Alkaloids
• Benzoxazinoides
• Cyanogenic Glucosides
• Glucosinolates
• Phenolics
• Terpenoids
28

29. Examples of plant Bioactive Specialized Compounds with insecticidal activity
Ibanez et al., 2012 29

30. Cont…
30

31. Hypersensitive response
• Plant’s response to herbivore results in the
formation of necrotic plant tissue and neoplamal
growth that isolates the invader from plant
• Plants can cast eggs off their leaves
• When an insect deposits its eggs onto a plant,
the plant may respond with growth of neoplastic
tissue and formation of necrotic tissues that
results in detachment of eggs
31

32. Oviposition fluid derived elitor induces neoplasmal growth in
response to Bruchids in Peas
Doss et al., 2008
32

33. Reymond et al., 2013
Oviposition by Pieris brassicae causes hypersensitive
response on Arabidopsis
33

34. (a) Egg of small cabbage white butterfly, inducing hypersensitive
response–like necrosis in Brassica nigra.
(b) Egg of Heliothis subflexa inducing neoplastic growth in Physalis
angulata leaf.
Hilker and Fatouros, 2014 34

35. Hypersensitivity response to Colorado Potato Beetle
oviposition in potato
Balbyshev and Lorenzen, 1999
35

36. Digestibility Reduction
• Plants produce a number of defense compounds
that reduce insect herbivores ability to digest the
plant derived nutrients
Proteinase Inhibitors
 -amylase inhibitorsα
 Lectins
Chitinases
 Polyphenol oxidases
36

37. Proteinase Inhibitors
• Different classes of proteinases, (trypsin-like,
chymotrypsin-like, and elastase-like proteases)
found in the midgut region of the insect
digestive tract, are used by insect herbivores to
cleave internal peptide bonds in plant proteins
37

38. Role of Tomato protease inhibitor in Plant Immunity to Insect Herbivores
Yan et al., 2013
38

39. α-Amylase Inhibitors
• The lectin-like -amylase inhibitors ( -AI)α α
are known to produce in cereal, such Wheat,
Barley, Sorghum and Maize
• The activities of these inhibitors are directed
against -amylases of insects, used for starchα
breakdown
39

40. Lectins
• Lectins are sugar-binding proteins produced
by plants as a defense response
• When lectins come into contact with the
glycoproteins lining the intestinal area of
insect herbivores, they are assumed to inhibit
the absorption of nutrients
40

41. Quantification of NICTABA accumulation in tobacco leaves after feeding
by
different herbivores
Vandenborre et al., 2011
41

42. 42

43. Chitinases
• Chitin is present in the exoskeleton and
peritropic membrane of insects
• Role in defense against herbivore by disrupting
the gut peritropic memberane
43

44. Polyphenol oxidase
• Polyphenol oxidases (PPOs) are anti-
nutritive enzymes
• Catalyze the oxidation of phenolics to
quinones, which decrease the nutritive value
of the wounded plant by crosslinking with
the nucleophilic side chains of proteins and
free amino acids
• Evidence for PPO involvement in plant
defense against insect herbivores includes
transcriptional induction of PPO genes by
44

45. Amino acid deaminases
• Amino acid deaminases are another group
of anti-nutritional proteins in plant
defense against insect herbivores
• These enzymes will degrade free amino
acids in the insect gut, removing nutrients
from the herbivore
45

46. Plant defensive proteases, lectins, amino acid deaminases, and
oxidation enzymes
Chen, 200546

47. Reallocation of Resources
• To protect valuable resources, they
might be reallocated by the plant upon
attack
47

48. Allocating nitrogen away from a herbivore
Newingham et al., 2007
Spotted knapweed
knapweed
moth
48

49. Indirect Defense Response
The term “indirect defense” is used when
plants attract, nourish or house other
organisms to reduce enemy pressure.
• Herbivore-induced plant volatiles
• Extrafloral Nectar
49

50. Herbivore-induced plant volatiles
• Herbivore-induced plant volatiles (HIPV)
can mediate indirect defenses, i.e., by
attracting foraging carnivorous predators and
parasitoids that kill herbivores
50

51. Herbivore-induced plant volatiles (HIPV)
HIPVs Plant Herbivore Natural Enemy
β-caryophyllene
β-ocimene
Tobacco H. virescens Cardiochiles nigriceps
(E)-β-farnesene
(E)-caryophyllene
(E)-α-bergamotene
Maize S. littoralis Cotesia marginiventris
(E)–4,8–dimethyl-1,3,7-
nonatriene
Maize M. separata Exorista japonica
Cotesia kariyai
linalool
α-pinene
1-hexanol
Maize M. separata Exorista japonica
Campoletis chlorideae
Rodrigues et al., 2014
51

52. • Herbivore-induced plant volatiles (HIPV)
are also involved in the plant
communication
• HIPVs will helps in the defense priming
in the neighboring plants
52

53. Model of defense priming in plant-herbivore
interactions
53Frost et al., 2008

54. Extrafloral Nectar
• Extrafloral nectar (EFN) appear in
more than 70 plant species
spanning angiosperms,
gymnosperms and ferns, indicating
that it is evolutionary more ancient
than floral nectar
• In contrast to floral nectar, used to
attract pollinators, EFN is secreted
on leaves and shoots to attract
predators and parasitoids
54

55. Extrafloral nectar as an herbivore-induced defense trait
Family Species Herbivore Trait enhanced
Bignoniaceae Catalpa bignonioides
(Indian bean)
Ceratomia catalpae
(Catalpa Sphinx)
Sugar content in EFN
Euphorbiaceae Ricinus communis
(Castor)
Spodoptera littoralis EFN volume
Euphorbiaceae Triadica sebifera
(Chinese tallow tree)
Gadirtha inexacta,
and
Grammodes geometrica
Secretion of total
solids
Malvaceae Gossypium herbaceum
(Cotton)
Spodoptera littoralis EFN volume
Martin, 2015
55

56. Ant visitation to extrafloral nectaries decreases herbivory and
increases fruit set in Chamaecrista debilis
Alves and Claro 2010
56

57. Conclusion
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58. Nature has blessed me
with Defense
mechanism
T
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