Ph.D. Scholar, IGKV, Raipur (C.G.)

1. welcome

2. Doctoral seminar
Role of silica in insect
plant interaction
Presented by
Manisha Netam
Ph.D scholar previous year
Seminar in-charge
Dr. S S Shaw
Professor
Department of Entomology

4. Introduction- What is silicon
Elemental silicon (Si) , is the
second most abundant element
in the earth’s crust , which is
mainly composed of silicates.
( McKeague and Cline 1963)
Discovered in 1824
Discovered by- Jons Jacob Berzelius
Origin of name- Latin word: silex, means flint

5. Si in Soil
Silicon is abundant in the soil but primarly in the form of quartz
(SiO2) which is inert and consequently is unavailable for plant
uptake.
(Epstein 1999)
Si ranging from
50 to 400 g/kg soil.
(D. S. Orlov, 1985. )
Solubility of all the above Si forms is low and biogeochemically
immobile. (V. V. Matychenkov,1996)
Oxide form of si Silicate form of si
Quartz Asbestos
Sand Granite
Amethyst Hornblende
Agate Feldspar
Flint Clay
Opal Mica

6. Different fractions of silicon in soils (Modified from Matichencov and
Bocharnikova (2001) and Sauer et al. (2006))

7. Plants uptake silicon in the form of monosilicic acid,
H4SiO4, since this is the only form of water-soluble
silicon.
• Monosilicic acid occurs mostly in a feebly adsorbed
condition and has low capability to migrate inside the
soil.
• The concentration of Si in plants varies between 0.1 and
10% by weight on a dry basis, but the ability of the plants
to accumulate Si varies widely between species.
(Epstein, 1994; Epstein, 1999)

8. Importance of Silicon for plants
Silicon has generally not been considered essential for
plant growth.
International Plant Nutrition Institute [IPNI] (2015),
Georgia, USA has listed it as a “beneficial substance”.
Although it is well recognized that many plants,
particularly Poaceae, have substantial plant tissue
concentrations of this element.

9. Variability of Si Contents in Various Plant
Species
Plants that absorb the largest amount of silicon
• Sugarcane (Saccharum officinarum) 300–700 kg/ha,
• Rice (Oryza sativa) 150–300 kg/ha
• Wheat (Triticum spp.) 50–150 kg/ha
(G. H. Snyder et. al,2006)
Monocotyledon plants Dicotyledonous plants
Wheat (Triticum spp.) Cucumbers (Cucumis sativus)
Barley (Hordeum vulgare L.) Melons
Ryegrass (Lolium perenne) Strawberries
Maize (Zea mays ) Soybeans (Glycine max L.)

11. Silicon transportation in plants
Silicon is mostly taken up by plants via the transpiration
stream(i.e., passive uptake)
Active silicon uptake is exhibited by some plant species
including rice Oryza sativa L.
Silicon is transported in the plant through the xylem via
apoplastic transport as monosilicic acid and deposited as
solid, amorphous, hydrated plant silica (SiO2.nH2O).

12. Ma & yamaji,2006

13. Silicon uptake
Active uptake Passive uptake
• Wheat cucumber
• Ryegrass melon
• Barley strawberry
• Rice soyabean
Zhang et al 2015

14. • According to their ability to accumulate Si, plants are classified into
High (10–15%)
include wetland grasses
(e.g., rice, bamboo and sugar cane)
• Medium (1–3%)
includes terrestrial grasses
(e.g., wheat),
Low (<1% Si dry mass, dm)
commonly eudicots
( eg.tomato)

16. The role of Si in enhancing the resistance of
plants to Abiotic stresses
A number of studies have showed that Si alleviates
• Physical stresses,
• Low and high temperature,
• Wind, drought and waterlogging,
• Low and high light and including radiation so on.

17. Silicon and water stress
Silicon can alleviate water stress by decreasing transpiration
Silicon can reduce the transpiration rate by 30% in rice,
which has a thin cuticle. (Ma et al. 200l a)
Under water-stressed conditions
(low humidity) the effect
of Si on rice growth was
more pronounced than on
rice that cultivated under
non-stressed conditions
(high humidity)

18. Silicon and phosphorous
• The uptake of P was not affected by the Si supply at
a low P level in both soil and solution culture.
(Ma and Takahashi 1990a, b, 1991)
• However, the uptake of Fe and Mn significantly
decreased in the Si-treated plants.
Since P shows a high affinity with metals such as Fe
and Mn, internal availability of P could be controlled
by the level of Mn, Fe, and other metals when the P
concentration is low.
(Nagaoka 1998).

19. Silicon and N excess.
• Excess N causes lodging, mutual shading,
susceptibility to diseases and so on.
• Silicon deposited on the stems and leaf blades
prevents lodging and mutual shading
• Si are especially important in the cultivation
systems with dense planting and high N
application.
(N. Ohyama,1985)

20. The role of Si in enhancing the resistance of
plants to Biotic Stresses
1).Silicon and rice blast disease
• The suppressive effect of Si on rice blast was reported as
early as 1917 by Onodera (1917).
• Rice blast, caused by Magnaporthe grisea (Hebert) Barr, is
the most destructive fungal disease of rice.

21. • Silicon reduces the epidemics of both leaf and
panicle blast at different growth stages.
Fig:A Fig:B
Rice grown without silicon treatment Si treated plant less effected
infected with neck blast disease. to neck blast disease.

22. Rice bacterial blight caused
by Xanthomonas oryzae
is a serious disease worldwide.
In Cultivar TNI which is
susceptible to this disease
the Si content in the leaves
Was lower than that of
the resistant breeding line,
TSWY7 under the nutrient
cultural system adopted.
Chang et al. (2002)

23. Silicon deposition in Poaceae

24. Crop Insect Species Resistance Mechanism
Grasses
Lolium perenne L.
Festuca ovina L.
Locust
Schistocerca gregaria
Mechanical protection of resources in
chlorenchyma cells
Rice Rice leaf folder
Cnaphalocrocis medinalis
Induced defence based on HIPV
production
Rice Asiatic rice borer
Chilo suppressalisWalker
Impeded stalk penetration and prolonged
penetration duration by early instar larvae
Rice Brown planthopper
Nilaparvata lugens Stål.
Antibiotic and xenobiotic effects targeting
insect physiological functions
Rice Brown planthopper
Nilaparvata lugens Stål.
Physical barrier and induced chemical
defences
Rice Brown planthopper
Nilaparvata lugens Stål.
Modulation of callose deposition
corn Armyworm
Spodoptera frugiperda
Affected biological parameters (fecundity
of females)
Fadi Alhousari and Maria Greger,2018

25. Silicon and powdery mildew disease
• Powdery mildew disease, caused by Sphaerotheca
juliginea, in a number of plant species.
• Foliar application of Si has been reported to be effective
in inhibiting
powdery mildew
development on
cucumber,
muskmelon,
grape leaves.
(Bowen et al.1992; Menzies et al. 1992).

26. Silicon and other diseases
Silicon is also effective in increasing the resistance to
the fungal diseases in cucumber roots caused by
Pythium ultimum
Pythium aphanidermatum
(Cherif et al. 1994)

27. Silicon and Mechanisms of Plant Resistance to
Insect Pests
• Arthropod pests are biotic stressors attacking plants
above and below the ground. (Kogan, M.; Lattin 1999)
• Plants counter act insect attacks both directly and
indirectly
• Direct defences associated with host morphological traits
• Indirect defences are mediated by host plant volatiles or
by herbivore-induced plant volatiles (HIPVs) released in
response to insect feeding.

29. • It is now well established that Si enhances plant resistance
and reduces plant damage caused by pathogens, insect pests
and non-insect pests through the mediation and up regulation
of both resistance Mechanisms.
(Ma, J.F.2004, Liang, Y.;et al 2015)
• Silicon suppresses insect pests such as stem borer, brown
planthopper, rice green leafhopper, and whitebacked
planthopper, and noninsect pests such as leaf spider and
mites . (Savant et al. 1997).
• Si deposition patterns within plant tissues led to the
hypothesis of mechanical or physical barriers to insect
feeding, as silica makes plant tissues difficult for insects to
efficiently chew, penetrate and digest.
(Kvedaras et al 2007.Reynolds 2009)

30. Formation of Physical Barriers to
Insects

31. Formation of Physical Barriers to Insects
• Silicon is deposited as a 2.5-m-thick layer just beneath
the cuticle layer (0.1 m thick), forming a silicon–cuticle
double layer in rice leaf blades. (Yoshida et al.,1962)

32. • The abrasiveness of silicified leaves and other plant
tissues leads to the increased irreversible wear of
mouthparts when insects are feeding, therefore
deterring chewing insects. (Massey et al.,2009)
• The insect midgut epithelium plays an important role
in food digestion . (Smagghe et al.,2001)
• Si could damage the ultrastructure of the midgut
epithelium, mainly through detachment of epithelial
cells from the basement membrane as observed in
larvae of the leaf miner Tuta absoluta fed Si-treated
leaves of tomato. (Dos Santos et al.,2015)
• Si is involved in toughening plant tissues, acting
indirectly by delaying insect penetration of host
tissues.

33. Silicon-Mediated Induced Resistance to Insects
• In addition to acting as a mechanical barrier, Si
can reduce pest damage by enhancing the induced
chemical defences of plants following insect
attack.
• Silicon acts as an abiotic elicitor of systemic
stress signals, mediated by phytohormone
pathways,leading to the efficient synthesis of
defensive compounds.
( Fauteux et al.,2005)

34. • The common phyto-hormones salicylic acid (SA),
Jasmonic acid (JA) and ethylene play primary roles
in orchestrating plant defence responses .
(De Vos et al.,2005)
• Defence against phloem-feeding insects is regulated
by both SA and JA signals.
(Moran et al., 2001)
• The strong interaction between Si and JA against
insects is accumulating, this being considered a
possible mechanism by which Si enhances
resistance to insect pests.

35. Si and Chewing Insect Pests
• Si may trigger different plant species to emit,
amplify, and/or alter HIPVs.
• chemical compounds are emitted by plants in
reaction to insect-induced damage in the form of
HIPVs.
• These compounds can act either as direct
attractants or repellents of insects.
(Liu et al.,2017)

36. • In response to feeding by the rice leaf folder (C.
medinalis), a wild-type rice plant supplied with Si mounts
a strong indirect defence based on HIPV production.
• These changed HIPV profiles then significantly enhanced
the attraction of adult females of the
• Trathala flavo-orbitalis and Microplitis to the Si-treated
plants attacked by C. medinalis.
• The signalling pathways that allow rice plants to mount
resistance against the chewing insect C. medinalis are JA
dependent.
(Liu et al.,2017)

37. Si and Phloem Feeders
• Insect phloem feeding can be inhibited at three
stages: before food ingestion, during ingestion or
after digestion and food absorption.
• Based on Electrical penetration graphs (EPGs)
findings reduction of both duration of phloem
ingestion and proportion of the brown
planthopper (N. lugens) individuals ingesting
phloem were observed on rice amended with Si.

38. • Electrical penetration graphs (EPGs) allowed
monitoring of the behavioural responses of insects
during probing and feeding and exploration of
interference with probing by chemical or physical
factors within the plant tissues and of the
localization of resistance within plant tissues.
• Silicon-induced resistance to N. lugens is
associated with increased accumulation of callose
deposition in the sieve tubes blocks the mass flow
of phloem and prevents phloem sap leakage
following feeding puncture.
(Gomes et al.,200), (Costa et al.,2011)

39. Si-Induced Resistance below Ground
Induced defences mediated by JA signalling have
been found to improve rice resistance to the rice
water weevil (Lissorhoptrus oryzophilus), whose
larvae feed on rice roots under flooded conditions.
(Lu et al.,2015)
• Below ground, the larvae of Diabrotica speciosa
(Coleoptera: Chrysomelidae) damage plant roots and
create holes in the tubers of the potato (Solanum
tuberosum L.), whereas the adults consume the
leaves.

40. • Foliar applications of silicic acid, an inducer of plant
resistance, increased plant protection against defoliators
and decreased tuber damage, reducing the number of
holes in the tubers of treated plants.
• This reduction in tuber attack was correlated with the
reduced leaf damage in the plants treated with silicic
acid. (Assis et al,.2012)
• Moreover, root-applied Si optimizes the mechanical
characteristics of rapeseed by increasing the root
diameter, breaking strength and expression levels of the
key genes related to stem lignin biosynthesis.
(Kuai et al,.2017)

41. Conclusion
• Si has a central role in boosting plants’ direct and indirect
defences against many insect pests via two Si-based
mechanisms: strengthened physical or mechanical barriers and
biochemical/molecular mechanisms that induce plant defence
responses.
• The overall conclusion that plants employ both Si-based
resistance mechanisms synergistically rather than singly,
relying on combined physical, chemical and biochemical
mechanisms to reduce damage by insect pests. Though
theaccumulation of Si differs among plant species, they likely
display similar Si defence mechanisms against insects.

42. THANK YOU