1. #35 - Salinity HORT 301 – Plant Physiology November 22, 2010 Taiz and Zeiger, Chapter 26, Web Topic 26.6 paul.m.hasegawa.1@purdue.edu Epstein and Bloom 2005

2. Salt stress is caused by ion concentrations greater than that required for optimum growth NaCl is the primary cause of soil and water salinity

3. Courtesy of Tim Flowers Biogeochemical cycling, incursions and inadequate management practices cause salinity stress

4. Cultivated Land (dry land)1500 million ha Salt affected 32 million ha (2%) Irrigated Land 230 million ha Salt affected 45 million ha (20%) Munns (2005) New Phytol World wide salinity problem

5. 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

6. Relative salt tolerance of halophytes and glycophytes

7. Primary Water deficit Ion disequilibrium (NaCl), Na + reduces K + acquisition K + deficiency Secondary Reduced cell expansion Protein denaturation Reduced membrane function Reduced assimilate production and metabolic activities Production of reactive oxygen intermediates (ROS) Salinity causes hyperosmotic stress (water deficit) and ionic disequilibrium (ion toxicity)

8. Salinity causes rapid osmotic stress and then ion disequilibrium in leaves Munns and Tester (2008) Annu Rev Plant Biol

9. 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

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

11. Plett et al. (2010) Plant, Cell & Environ 33, 612-626 Cellular Na + homeostasis

12. [Na + ] ext ↑ → [Ca 2+ ] cyt ↑ → SOS3 → SOS2 → SOS1 SOS3 - Ca 2+ binding protein, SOS2 - kinase, SOS1 - H + driven Na + antiporter [Ca 2+ ] ext blocks Na + uptake through NSCC 26.16 Regulation of ion homeostasis by the SOS signal transduction pathway Salt stress signaling regulates Na + ion homeostasis

13. 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

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

15. Na + transport across the root is regulated in the cortex and at xylem loading Tester & Munns (2008) Annu Rev Plant Biol

16. SOS1 and NHX1 Na + -H + antiporters SOS1 – Na + exclusion at the plasma membrane NHX – Na + compartmentalization into the vacuole

17. Pardo, 2010 HKT1 regulates Na + loading into the xylem Na,K Vacuole NHX

18. 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)

19. Relationship between EC and yield of durum wheat cultivar Tamaroi with Nax2 gene + Nax2 - Nax2

20. 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

21. J2731* J2731*UAS:HKT 100 mM NaCl 0 mM NaCl % Salinity tolerance Stelar-specific AtHKT1;1 activation in Arabidopsis increases salinity tolerance 100 mM NaCl 0 mM NaCl salt sensitivesalt tolerant Møller et al. (2009) Plant Cell 21: 2163–2178

22. Salt Tolerance of Canola by Expressing NHX1 Tonoplast Na + /H + Antiporter Zhang et al. (2001) PNAS 200 mM NaCl

23. Salt/Drought Stress Tolerance of Rice through Expression of Genes that Result in Trehalose Accumulation Garg et al. (2002) PNAS

24. Genetic Determinants of Salt Tolerance Genetic determinants that are regulators and effectors of salt tolerance are being identified Forward genetics – phenotype to gene Mutational genetics (model systems) Genetic variation in natural and domesticated populations (crops) Reverse genetics – candidate gene to phenotype Allelic variation – transgene technologies Allelic variation – QTL and association mapping of natural and domesticated populations for gene identification and genetic introgression – nonGMO approach