1. 20. Root exudates-diversity of chemical constituents
21 Rhizosphere chemistry. Soluble and VOC – phenols & terpens
22 Interaction of root metabolites and root associated microorganism
2. • In 1904 Lorenz Hiltner first coined the term
"rhizosphere"
• Rhizosphere as the area around a plant root that is
inhabited by a unique population of microorganisms
influenced, by the chemicals released from plant roots.
• Rhizosphere definition has been refined to include three
zones which are defined based on their relative
proximity to, and thus influence from, the root.
• The endorhizosphere includes portions of
the cortex and endodermis in which microbes and cations can
occupy the "free space" between cells (apoplastic space).
• The rhizoplane is the medial zone directly adjacent to the root
including the root epidermis and mucilage.
• The outermost zone is the ectorhizosphere which extends from
the rhizoplane out into the bulk soil.
• Rhizosphere is not a region of definable size or
shape, but instead, consists of a gradient in
chemical, biological and physical properties which
change both radially and longitudinally along the
root.
Rhizosphere
3. Rhizodeposits
• 10-40% of their total photosynthetically fixed carbon.
• The C released is in both organic (e.g., low molecular weight organic acids)
and inorganic (e.g., HCO3) forms
• Organic forms are the most varied and can have the most influence on the
chemical, physical and biological processes in the rhizosphere
• The composition and amount of the released compounds is influenced by
many factors including
• plant type,
• climactic conditions,
• insect herbivory,
• nutrient deficiency or toxicity, and
• the chemical, physical and biological properties of the surrounding soil.
• The root products imparted to the surrounding soil are generally
called rhizodeposits.
• Rhizodeposits have been classified based on their chemical composition,
mode of release, or function but are classically defined to include
• sloughed-off root cap and border cells,
• mucilage, and
• exudates.
1 loss of cap and border cells,
2 loss of insoluble mucilage,
3 loss of soluble root exudates,
4 loss of volatile organic carbon,
5 loss of C to symbionts,
6 loss of C due to death and lysis of root epidermal and
cortical cells.
8. Rhizospheric microbiome composition based on high throughput analysis of
three plant species Arabidopsis, maize and rice
Bias et al.,2014
The composition of the microbiome in plants is dynamic and controlled by multiple factors.
In the case of the rhizosphere, temperature, pH, and the presence of chemical signals
from 55 bacteria, plants, and nematodes all shape the environment and influence
which organisms will flourish
11. Maize roots respond to feeding by larvae of the beetle
Diabrotica virgifera virgifera by releasing (E)-β-caryophyllene
(Eβc). This insect-induced root volatile attracts
entomopathogenic nematodes (EPN) and thereby helps to
protect the roots against herbivore damage.
12. Drivers of Microbial Community Structure Inside the Root
Endophyes influence plant growth
(purple arrow) through the
•release of phytohormones
(phytostimulation),
•increasing the supply of nutrients
(biofertilization) and
•providing protection from
phytopathogens (biocontrol).
13. • Rhizodeposition,
• Nutrient cycling and transformations,
• Quorum sensing,
• Rhizodegradation,
• Carbon sequestration and
• Ecosystem functioning
15. Changes in roots system architecture (RSA) of barely (Hordeum vulgare) in response
to zones of high phosphate, nitrate, ammonium and potassium availability
• Plants respond to nutrient deficiency by altering root morphology, recruiting the help of microorganisms and changing the chemical
environment of the rhizosphere.
• Components in root exudates assist plants in accessing nutrients by acidifying or changing the redox conditions within the
rhizosphere or directly chelating with the nutrient.
• Exudates can liberate nutrients via dissolution of insoluble mineral phases or desorption from clay minerals or organic matter
where they are released into soil solution and can then be taken up by the plant.
• Plants respond differently depending on the form of nitrogen in the soil. Ammonium has a positive charge, and thus the plant
expels one proton (H+
) for every NH4
+
taken up resulting in a reduction in rhizosphere pH. When supplied with NO3
-
, the opposite
can occur where the plant releases bicarbonate (HCO3
-
) which increases rhizosphere pH. These changes in pH can influence the
availability of other plant essential micronutrients (e.g., Zn, Ca, Mg).
• Phosphate (PO4
3-
), the form of P used by plants, is highly insoluble in soils, binding strongly to Ca, Al and Fe oxide, and soil organic
matter rendering much of the P unavailable to plants.
Iron deficiency elicits a response from plants which generally differs
depending on whether the plant is a dicot or monocot. Dicots respond to
Fe deficiency by releasing protons into the soil environment and increasing
the reducing capacity of the rhizodermal cells. In monocots, Fe deficiency
triggers the release of phytosiderophores such as mugienic acid which is
a non-proteinogenic amino acid with extremely high affinity for Fe. The
phytosiderophore chelates strongly with Fe and is then brought back to the
root via diffusion where plasma membrane transporters specific to the
chelated Fe shuttle it into the cells.
16. Plants produce a wide range of organic compounds including sugars,
organic acids and vitamins, which can be used as nutrients or signals by
microbial populations. On the other hand, microorganisms release
phytohormones, small molecules or volatile compounds, which may act
directly or indirectly to activate plant immunity or regulate plant growth and
morphogenesis.
Metabolites: Microbial Volatile Organic Compounds in Plant Health (mVOC)
Volatile organic compound mediated interactions
at the plant-microbe interface
17. Mhlongo et al 2018. Frontiers in Microbiol.
Metabolomics studies of signaling between plant hosts and microorganisms…
18. Microbial siganlomics lead to trans-generational defence priming…
Mhlongo et al 2018. Frontiers in Microbiol.
22. Fe and Selenium absorption mediated by VOCs…
Wang et al., 2017
23. María et al., 2016
mVOCs for Plant Growth and Flowering…
28. Plant Growth Inducers: Differential regulation of genes and proteins modulated by VOCs from Bacillus…
• Cheaper,
• Effective,
• Efficient, and
• Eco-friendly
30. Lee et al ., 2012
Elicitation of Plant Systemic Defense…
31. Tyc et al., 2017
Ecological role by Metabolites…
32. B
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tain
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G
e
ran
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l
is
o
v
ale
rate
C
h
o
lin
e
F
u
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aric
acid
B
u
tan
o
ic
acid
Volatilome pattern of Multifunctional Bacillus altitudinis FD48 ensures drought protection
Bacillus altitudinis FD48
mVOC analysis by GCMS-TD
Proposed Mechanism
Drought stress alleviation by
Acetoin biosynthesis
Trapping head space volatiles in Tenax TA coated sorbent tubes
PEG+
PEG-
Proposed mechanism : Drought defence
response by production of Butanediol and
osmolytes .
Metabolic profiling of Bacillus altitudinis FD48 showed the production of drought conferring compounds
(Acetoin, Choline and Betaine aldehyde cation, Geranyl isovalerate, Butanoic acid, Fumaric acid under
moistue stress (-7.05 bars osmotic potential) revealed the prime role of B. altitudinis FD48 in drought
mitigation
33. Small molecules in defnce signaling against drought stress through IST by B.altitudinis FD48
P
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Proposed mechanism : Drought
defence response activated by SA
singalling
B. altitudinis FD48
B
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N-(
N-g
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-L-le
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)-
B. altitudinis FD48 supplemented with PEG
PEG-
PEG+
Proposed Mechanism:
Stomatal closure mediated by
signalling pathway such as SA
signalling pathway.
34. P
h
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n
y
la
la
n
in
e
P
ro
lin
e
Phenylacetic acid
Osmotic stress
Heat stress
PEG +
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A
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P
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Phenylacetic acid
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d
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t
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le
t
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)
-
Secondary metabolites of Multifunctional Bacillus altitudinis FD48 conferring drought
protection
PEG-
-
Upregulation of proline and
phenylalanine
Phenol, ϒ-aminobutyric acid (GABA)
pronounced under moisture stress
Phenyl acetic acid is common
Proposed
mechanism
GABA and proline enhances the activity of
photosynthetic system under osmotic and heat stresses
35. Metebolomic footprint of apoplastic fluid of rice and their functional insights
Distribution pattern
Correlation based pathway network Rice apoplast metabolome
Apoplast metabolomes fights abiotic stress
• FA synthesis
• Purine metabolism
• Arginine and glutamate
synthesis
• Tyrosine metabolism
• Urea cycle
Plant hormonal Signal
transduction
Punitha, Kalarani & Sivakumar
36. Apoplast associated microbes offer drought tolerance and
hormonal regulation in rice...
Screening for drought tolerance
phytohormone production, enzymatic
activity, osmoprotectants and
exopolysaccharide production
Infiltration centrifugation
method
(Nouchi et al., 2012)
ABA production in bacterial and yeast isolates
ABA 100 PPM
B.methylotrophicus RABA 6 Candida tropicalis RAYN2
Bacillus methylotrophicus RAB6 and
Candida tropicalis RAYN2 had tolerance
up to -10 bars of PEG concentration and
they performed better in PGP activities.
B. methylotrophicus RAB6
Candida tropicalis RAYN2
Strain IAA (µg ml-1
) ACC deaminase (nmoles of α
ketobutyrate mg-1
protein h-1
)
RABA 6 15 149
RAYN2 14 248
ABA ABA
37. Apoplast associated microbes (bacteria and yeast) imparts significant role in the root secretome
of rice under moisture stress (Var. Co51)
Root exudate collection
Metabolite diversity in root secretome Apoplastic microbe inoculated seedlings under
hydrophonics sytem
More diversity under drought upon
interaction of B. methylotrophicus
RABA6 with C.tropicalis RAYN2
Sugars, amines (glycine), fatty
acids, phenols, benzene
derivatives – recruit beneficial
microbes in the rhizosphere ???
Punitha, Kalarani & Sivakumar
38. Effect of apoplast associated microbes for moisture stress resilence in rice (Var. Co51): a invitro
study under pot culture with focus on RSA traits and ROS enzymes
Root architecture – WinRhizo®
•Apoplastic bacterium B. methylotrophicus
RABA6 increased the root surface area, root
volume, average diameter, no. of tips and folks
under drought followed by C.tropicalis RAYN2 .
•Co-inoculum had adverse effect on RSA traits –
might be due to allelopathic effect of some
metabolites produced by either one of the
partner.
Root tips
Root volume
Surface area Root diameter
Punitha, Kalarani & Sivakumar
39. Metabolites induced drought stress response by Yeast, Cystobasidium minutum RAYA2
2,3-B
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san
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,
10-m
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-
Coum
arin
-
6-ol,
3,4
-dihydro
-4,4-
dim
e
thyl
-5,7-dinitro
Hexad
ecane
2,3 Butanediol
PEG+
PEG-
PUNITHA S., PhD Scholar
Punitha, Kalarani and Sivakumar, 2018
40. • AMF inoculated black gram plants showed enhanced
defense as confirmed by the increased level of total
phenolic content and defense enzymes (Peroxidase.
Phenol oxidase, catalase, superoxide dismutase,
phenyl alanine ammonia lyase, & Total Phenols).
• Defense related volatile compounds; terpenoids,
benzanoids, fatty alcohols, phenyl propanoid and
sulphur containing compounds were identified in
AMF infected black gram.
• Mychorrized black gram plants have reduced the
feeding capability of the targeted insect S. litura, by
activation of SA and JA pathways
Volatile collection
Volatilome fingerprint by untargeted metabolomics
AMF black gram pronounced salicylic and jasmonic acid
upon interaction with S.litura - key players in phenyl
propanoid pathway, elliciting plant defense.
Induction
of
Salicyclic
acid
pathway
S. Ananda Kumar, T. Kalaiselvi and U. Sivakumar
AMF
#35:
Metabolomics analysis of the apoplastic fluid revealed that drought tolerance genotypes comprises distinct metabolites which are responsible for drought tolerance capacity (Benzoic acid, glucopyranoside, trans-geranylgeraniol, ascorbic acid, asparagine and dodecanoic acid).
![Small molecules in defnce signaling against drought stress through IST by B.altitudinis FD48
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Proposed mechanism : Drought
defence response activated by SA
singalling
B. altitudinis FD48
B
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id
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u
cy
l
)-
B. altitudinis FD48 supplemented with PEG
PEG-
PEG+
Proposed Mechanism:
Stomatal closure mediated by
signalling pathway such as SA
signalling pathway.](https://image.slidesharecdn.com/lec20to22rootexudatesmetab-250310160605-1bdb54de/85/Lecture-20-to-22-Root-exudates_Metab-ppt-33-320.jpg)
