Salinity has been a key abiotic constraint devastating crop production worldwide. Attempts in understanding salt tolerance mechanisms has revealed several key enzymes and altered biochemical pathways inferring resistance to crop plants against salt stress. Rice (Oryza sativa L.), being a glycophyte by nature, is severely impacted in presence of excess salt. It is susceptible to salinity specifically at the early vegetative and later reproductive stages. The response of the crop to excessive salt toxicity can be fully understood by analysis of four different domains i.e., physiochemical responses, genetic changes, genome alterations and molecular cascades.
Rice plants generally tolerate salt by mainly three mechanisms; ion exclusion, osmotic tolerance and tissue tolerance, which involve Na+ and Cl- transport process at cellular and whole plant levels (Roy et al., 2008). Under salinity, up-regulation of genes (OsHKT1:1, OsHAK10 and OsHAK16) advances the accumulation of Na+ and increased compartmentalization in old leaves. Salt overly sensitive (SOS) pathway extrudes Na+ out of the cell with the aid of vaculor transporter (NHX1) and Na+/ H+ antiporter.
Stress signaling molecules like Brassinosteroids, Jasmonic acid (JA), Abscisic acid (ABA) and Osmoprotectants like Proline, Glycine betaine etc. considerably reduce the impact of salinity on growth. There was an increase in salt tolerance in Pusa Basmati-1 on exogenous application of 24-epibrassinosteroid and also with the expression of codA (Choline oxidase) gene.
Like other crops, miRNA(micro RNA) genes, Ubiquitination genes and DNA methylation genes has opened new avenue for elucidating novel mechanisms of gene regulation of salt tolerance in rice.. Pokkali, a salt tolerant line showed more demethylation than a salt sensitive IR29.
Despite intensive studies, mechanisms underlying exclusion of Cl- and NO3- are yet to be addressed. An improved understanding of epigenetic regulation and changes in transcriptome, proteome, and metabolome of Rice during salt stress is crucial to gain deeper insight into mechanisms of salt tolerance.
2. By
SUPRITHA RAJ, D. S.
PALM8003
Senior M. Sc., Agri (GPB)
Department Of Genetics and Plant Breeding
MECHANISMS OF SALT
TOLERANCE IN RICE
By
SUPRITHA RAJ, D. S.
PALM8003
Senior M. Sc., Agri (GPB)
Department Of Genetics and Plant Breeding
3. Introduction
Effects of salinity stress
Phases of salt tolerance
Mechanism of salt tolerance
Confirmatory evidences
Conclusion
Contents of seminar
2
4. Introduction
•Salinity: It is caused due to high accumulation of Sodium,
Magnesium, and Calcium and then anions such as, SO4
-3
NO3
-, CO3
-2 , HCO3
- and Cl-, etc.
Classification of salt affected soils
Soil Type pH EC (ds/m) ESP SAR
Saline soil <8.5 >4 <15 <13
Sodic / alkali
soil
≥8.5 <4 >15 >13
Saline sodic /
saline alkali
≤8.5 >4 >15 >13
pH- concentration of H+ ions ESP- Exchangeable Sodium Percentage
EC- Electrical conductivity SAR- Sodium Absorption Ratio
3
Introduc
tion
5. Effects of salt stress
Salt
stress
Leaf
senescence
Oxidative
stress
Inhibits
protein
synthesis
Inhibits
enzyme
activity
Inhibits
photosynthes
is
Yield
reduction
Inhibits
seed
germination
Inhibits
water
uptake
Inhibits
root growth
and cell
elongation
Inhibits leaf
growth and
new leaf
production
4
6. Plant response to salt
stress
Osmotic phase Ionic phase
Munns and Tester , 2008
5
11. 1. Restricting initial entry of salts to roots
H2O
+
Na+
Na+
Na+
Na+
+
H2O
selective uptake of ions along with
water occur through
Apoplast pathway
Symplast pathway
NSCC
HKT
Munns and Tester , 2008 10
12. •To keep Na+ concentration low(10-30mM)
•To prevent toxic effects on cytosolic enzymes
•Difference in AtNHX1/ AtAVP1 affect vacuolar
sequestration
OsHKT1;1
OsHAK10
OsHAK16
OsNHX1
OsAVP1
Na+ accumulation
and
compartmentation
Wang et al., 2012
2. Intracellular compartmentation
11
13. 3. Cell Ion homeostasis
Transporters on cell
membrane
H+-pump ATPases,
Na+/H+ antiporter
high-affinity uptake of
K+ ion
Blumwald, 2000
symporter
H+ pumps present in the vacuolar
membrane:
vacuolar type H+-ATPase (V-
ATPase)
vacuolar pyrophosphatase (V
Ppase).
12
19. 4.2.Jasmonic acid
JAZ (JASMONATE ZIM DOMAIN) protein
family
In the absence of JA, JAZ proteins bind to
downstream transcription factors and limit
their activity
JA or its bioactive derivatives, degrade JAZ
proteins , freeing transcription factor.
JA
SCFCOI1
Degradation of JAz
Activation TFs (MYC
2,3,4)
Changes in gene
expression
18
Ye et al ., 2009
28. 6.3. Glycine betaine
Quarternary ammonium compound, soluble
Interact with hydrophobic and hydrophilic
compound
Accumulates in plastid and chloroplast and
provides tolerance against salt stress
Increase the activity of SOD, APX, GR,
Ion homeostasis
27
29. Materials: Pusa Basmati 1
Method: Agrobacterium mediated transformation of codA from Arthrobacter globiformis
28
30. 7. Aquaporins
integral membrane proteins
facilitate the transport of water and small neutral
molecules across biological membranes.
reported to transport various substrates, including
ammonia, boron, carbon dioxide, formamide, glycerol,
hydrogen peroxide (H2O2 ), lactic acid, silicon and urea.
Main category
Plasma membrane intrinsic proteins (PIPs),
Tonoplast intrinsic proteins (TIPs),
NOD26-like intrinsic proteins (NIPs)
Small and basic intrinsic proteins (SIPs)
29
Reddy et al., 2017
