Salinity Tolerance Advice from the Grain Biotech Australia Website

The threat to agriculture in Australian through dryland salinity is increasing at an alarming rate.
A supplement to the GMO Pundit page on Salinity Solutions.
Western Australia has the largest area of dryland salinity in Australia and the greatest potential for increased damage over the next 50 years (National Land and Water Resources Audit, 2000; http://audit.ea.gov.au). Currently 4.3 million hectares are susceptible to dryland salinity in the south-west region of Western Australia, with an expected 8.8 million hectares affected by 2050 (National Land and Water Resources Audit, 2000; http://audit.ea.gov.au).


Current estimates show a loss to agricultural production in Western Australia for 2050 of $300-400 million (in 2000 terms) (State Salinity Strategy 2000; http://www.salinity.org.au/management/pdfs/salinity-strategy.pdf). To reduce the impact of salinity on crop production in Australia and Western Australia salt tolerant varieties are required.

There have been numerous attempts to develop wheat varieties, through the integration of wild species using conventional breeding, with both salt tolerance and high yields of quality grain. This strategy has produced salt adapted lines however the level of salt tolerance is still relatively low. Recently research has turned to molecular approaches to develop salt tolerant crops. These approaches have incorporated a number of salt tolerance mechanisms into crop species allowing them to grow in ~ 1/3 sea water (200mM salt).

Plants have adapted to their environment by developing mechanisms which enable them to cope with abiotic stresses. These mechanisms can be separated into four categories: developmental (e.g. time of flowering), structural (e.g. leaf waxiness), physiological (e.g. compartmentalisation of ions) and metabolic (accumulation of osmolytes) (McCue and Hanson, 1990; Delauney and Verma, 1993). The major focus in engineering stress tolerant plants has been on the metabolic mechanism as this was seen as the most readily manipulated (McCue and Hanson, 1990). A key metabolic mechanism is the production of osmoprotectants. Osmoprotectants are inert compounds that can accumulate to high levels in the cytosol of stress tolerant plants allowing these plants to osmotically adjust to there environment (McCue and Hanson, 1990; McNeil et al., 1999). The production of osmoprotectants in plants that normally do not produce these compounds has been known to confer salt, water and frost tolerance on these plants (Hong et al., 2000; Konstantinova et al., 2002; Roosen et al. 2002).

While the major focus has been on metabolic mechanisms for producing abiotic stress resistant plants there has also been recent work on physiological mechanisms, specifically the compartmentalising of ions (Barkla et al., 1995). Salt stress is caused by a reduction in water potential and also by excess sodium ions which impact on critical biochemical pathways mainly found in the cytoplasm (Wyn Jones, 1981; Apse et al., 1999). The identification and subsequent cloning of a sodium pump (Na+/H+ tonoplast antiport) has helped to produce salt tolerant plants that can transfer sodium ions to the vacuole away from the cytoplasm (Barkla et al., 1995; Apse et al., 1999; Zhang and Blumwald, 2001).

The combination of different salt tolerance mechanisms in a commercial crop such as wheat holds great promise for a salt tolerant wheat variety that can tolerate a broad range of saline conditions.



LINKS TO SALINITY WEB PAGES

National Land and Water Resources Audit, 2000

http://audit.ea.gov.au/anra/land/docs/national/Salinity_Contents.html

State Salinity Council

http://www.salinity.org.au/management/

http://www.salinity.org.au/management/pdfs/salinity-strategy.pdf

CRC for Plant-Based Management of Dryland Salinity

http://www1.crcsalinity.com/



References

Apse, M.P., Aharon, G.S., Snedden, W.A., Blumwald, E. (1999) Salt tolerance conferred by over-expression of vacuolar Na+/H+ antiport in Arabidopsis. Science 285, 1236-1258.

Barkla, B. J., Zingarelli, L., Blumwald, E., Smith, A.C. (1995) Tonoplast Na+/H+ antiport activity and its energization by vacuolar H+-ATPase in the halophytic plant Mesembryanthemum crystallinum L. Plant Physiol 109, 549-556.

Delauney, A.J., Verma, D.P.S (1993) Proline biosynthesis and osmoregulation in plants. The Plant Journal 4, 215-223.

Hong, Z., Lakkineni, K., Zhang, Z., Verma, D.P.S. (2000) Removal of feedback inhibition of ?1-pyrroline-5-carboxylate synthetase results in increased proline accumulation and protection of plants from osmotic stress. Plant Physiology 122, 1129-1136.

Konstantinova, T., Parvanova, D., Atanassov, A., Djilianov, D. (2002) Freezing tolerant tobacco, transformed to accumulate osmoprotectants. Plant Science 163, 157-164.

McCue, K.F., Hanson, A.D. (1990) Drought and salt tolerance: towards understanding and application. Trends in Biotechnology 8, 358-362.

McNeil, S.D., Nuccio, M.L., Hanson, A.D. (1999) Betaines and related osmoprotectants. Targets for metabolic engineering of stress resistance. Plant Physiology 120, 945-949.

Roosens, N.H., Bitar, F.A., Loenders, K., Angenon, G., Jacobs, M. (2002) Overexpression of ornithine-d-aminotransferase increases proline biosynthesis and confers osmotolerance in transgenic plants. Molecular Breeding 9, 73-80.

Zhang, H-X., Blumwald, E. (2001) Transgenic salt-tolerant tomato plants accumulate salt in foliage but not in fruit. Nature Biotechnology 19, 765-768.