Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

Salt Stress
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sponse and yield (Subbarao and Johansen, 1994). In a recent study, on canola, field pea,
dry bean and durum wheat, several agronomic parameters have been evaluated for their
effects on salt tolerance, (Steppuhn et al., 2001). As screening for salt tolerance based
on visible symptoms (leaf necrosis, abscission and chlorosis) is appropriate only for
sensitive crops, and the classical method based on yield change is expensive, several
indirect parameters and related methods, such as chlorophyll fluorescence and leaf
bioelectric activity have been proposed (Shabala et al., 1998). Screening methods for
salt tolerance are grouped into the following categories (Munns and James, 2003): a)
methods based on growth (e.g. root and leaf elongation, biomass) and yield under
controlled conditions, including both short-term and long-term experiments; b) methods
of tolerance to high salinity levels, such as germination and plant survival, leaf
injury, premature loss of chlorophyll and measurements of chlorophyll fluorescence;
and, c) methods based on physiological mechanisms and specific traits, such as Na +
exclusion, K + /Na + discrimination and Cl - exclusion, as well as Na + /Ca 2+ selectivity (Zeng
et al., 2003).
Based upon the differences in physiological traits, several methodologies
have been developed, especially for the purposes of analyzing the ion concentration
and localization within particular tissues and cell compartments. In this category, the
benefits of microelectrode measurements for studying of single cell metabolism have
been advocated (Miller et al., 2001). Ion activities in living plant cells are recorded by
patch-clamp techniques (White et al., 1999), fluorescent dyes (Mühling and Läuchli,
2002b, Halperin and Lynch, 2003) and NMR technologies (Olt et al., 2000, Gruwel et al.,
2001), whereas X-ray microanalysis offers an opportunity for quantifying the amount of
an element (Flowers and Hajibagheri, 2001). The studies of nutrient status and transport
on the microscale rely on other methodologies as well, such as: the kinematic
growth analysis and elemental deposition rates, microdissection, specimen preparations,
secondary ion mass spectrometry, and other microanalytical techniques, like
microautoradiography (Lazof and Bernstain, 1999). Since the extrapolation of results
obtained under highly controlled conditions to real field situation has had limited success,
it was necessary to develop the new and simpler field screening methods and
models to enable more efficient breeding for salinity tolerance (Isla et al., 1997).
12. MODELING FOR YIELD ESTIMATION
There is no unique parameter relating crop yield to the average soil salinity, since crop
growth changes with soil water deficit and other soil features. There are mathematical
models for estimation of crop yield under saline conditions dealing with the physics of
water movement through soil, plant and atmosphere (Grant et, al., 1993). The model
named ecosys was expanded to include an ion transfer-equilibrium-exchange model
used to calculated electrical conductivity and soil osmotic potential, and it was proposed
for general use in assessing salinity effects on crop growth and water use on
different soils and environmental conditions (Grant, 1995). Some other models propose