#35 - SalinityHORT 301 – Plant Physiology

November 22, 2010Taiz and Zeiger, Chapter 26, Web Topic 26.6

paul.m.hasegawa.1@purdue.edu

Epstein and Bloom 2005

Salt stress is caused by ion concentrations greater than that required for optimum growth

NaCl is the primary cause of soil and water salinity

Courtesy of Tim Flowers

Biogeochemical cycling, incursions and inadequate management practices cause salinity stress

Cultivated Land (dry land) 1500 million ha

Salt affected 32 million ha (2%)

Irrigated Land 230 million haSalt affected 45 million ha (20%)

Munns (2005) New Phytol

World wide salinity problem

Plants are classified as glycophytes (sweet plants) or halophytes (salt plants)

Glycophytes are all other plants including crops

Smith et al. (2010)

Halophytes (salt plants) are natives of a saline environment, adapted

Relative salt tolerance of halophytes and glycophytes

PrimaryWater deficit Ion disequilibrium (NaCl), Na+ reduces K+ acquisition K+ deficiency

SecondaryReduced cell expansionProtein denaturationReduced membrane functionReduced assimilate production and metabolic activitiesProduction of reactive oxygen intermediates (ROS)

Salinity causes hyperosmotic stress (water deficit) and ionic disequilibrium (ion toxicity)

Salinity causes rapid osmotic stress and then ion disequilibrium in leaves

Munns and Tester (2008) Annu Rev Plant Biol

NaCl is a cytotoxin

Protein denaturation caused by Na+ and Cl-

(halophyte)

(glycophyte)

(halophyte)

Bray et al. (2000)

Metabolic enzymes of halophytes and glycophytes are equally sensitive to NaCl

Osmotic adjustment in NaCl environments – ion compartmentalization in the vacuole and compatible solute accumulation in the cytosol

Plett et al. (2010) Plant, Cell & Environ 33, 612-626

Cellular Na+ homeostasis

[Na+]ext↑ → [Ca2+]cyt↑ → SOS3 → SOS2 → SOS1SOS3 - Ca2+ binding protein, SOS2 - kinase, SOS1 - H+ driven Na+ antiporter

[Ca2+]ext blocks Na+ uptake through NSCC

26.16 Regulation of ion homeostasis by the SOS signal transduct ion pathway

Salt stress signaling regulates Na+ ion homeostasis

Smith et al. (2010) Plant Biology

Compatible osmotic solutes accumulate in the cytosol and organelles

Bray et al. (2000)

Compatible solutes maintain hydration shell around proteins

Xylem loading of Na+ and Cl- in roots controls ion accumulation in the shootNa+ and Cl- move radially across roots with the soil solutionMovement to the shoot is driven by transpirational flux

4.4 Pathways for water uptake by the root

Na+ transport across the root is regulated in the cortex and at xylem loading

Tester & Munns (2008) Annu Rev Plant Biol

SOS1 and NHX1 Na+-H+ antiporters SOS1 – Na+ exclusion at the plasma membraneNHX – Na+ compartmentalization into the vacuole

Pardo, 2010

HKT1 regulates Na+ loading into the xylem

Na,K

Vacuole

NHX

Transfer of Nax2 (TmHKT1;5) from Triticum monococcum (einkorn) into Triticum turgidum spp durum

(durum wheat) increases yield in saline soil by 25%

Rana Munns, Richard James and others (including Caitlin Byrt, Mark Tester, Ray Hare)

Relationship between EC and yield of durum wheat cultivar Tamaroi with Nax2 gene

ECa (DS/m)

260 280 300 320 340 360 380 400 420 440 460 480

Gra

in y

ield

(t/

ha)

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Block 1Block 2Block 3

+ Nax2

- Nax2

Plett et al. (2010) PLoS One 5, 1-8

Root cortical cell expression of HKT1 and reduced shoot Na+ accumulation and salt tolerance

Plett et al. (2010) PLoS One

50

75

100

J2731* J2731*UAS::HKT

E2586 E2586UAS::HKT

J2731* J2731*UAS:HKT

10

0 m

M N

aC

l

0

mM

Na

Cl

% S

alin

ity

tole

ran

ce

Stelar-specific AtHKT1;1 activation in Arabidopsis increases salinity tolerance

10

0 m

M N

aC

l

0

mM

Na

Cl

salt sensitive salt tolerant

Møller et al. (2009) Plant Cell 21: 2163–2178

Salt Tolerance of Canola by Expressing NHX1 Tonoplast Na+/H+ Antiporter

Zhang et al. (2001) PNAS

200 mM NaCl

Salt/Drought Stress Tolerance of Rice through Expression of Genes that Result in Trehalose Accumulation

Garg et al. (2002) PNAS

Genetic Determinants of Salt Tolerance

Genetic determinants that are regulators and effectors of salt tolerance are being identified

Forward genetics – phenotype to geneMutational genetics (model systems) Genetic variation in natural and domesticated populations

(crops)

Reverse genetics – candidate gene to phenotype

Allelic variation – transgene technologiesAllelic variation – QTL and association mapping of natural and

domesticated populations for gene identification and genetic introgression – nonGMO approach