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

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R.G. Trischuk, B.S. Schilling, M. Wisniewski and L.V. Gusta
alcohols which increase in the autumn during acclimation and decrease in the spring
during deacclimation (Levitt, 1980). Many wheat and canola cultivars show a parallel
relationship between sugars and freezing tolerance. The main sugars that increase are
sucrose, glucose, fructose, sorbitol, manitol, raffinose, and stachyose. It is postulated
sugars replace water and decreases the degree of freeze-induced dehydration. Trehalose
and umbelliferose have received considerable attention in the stress response as
they promote glass transitions that protect cells from desiccation injury (Crowe et al.,
1984, Wolkers et al., 1999). Stress induced proteins have a stabilizing effect on sugar
glasses by increasing the average strength of hydrogen bonding in the dry state (Wolkers
et al., 2001). Long chain fructans increase during cold acclimation of cereals and inhibit
ice growth in xylem vessels (Olien, 1967). Thylakoid membranes are protected from
freezing inactivation by exogenous proline, argenine, threonine and lysine. Proline and
glycine-betaine are both postulated to act as cryoprotectants. Yoshida and Uemura
(1984) observed the development of freezing tolerance was accompanied by an increase
in phospholipids, especially phosphatidyl choline and phosphatidyl ethanolamine.
Free fatty acids were shown to accumulate as degradation products from ROS
following a lethal-thaw event (McKersie and Bowley, 1996).
Previously, it was impossible to measure all these changes simultaneously;
however, ultra-high resolution mass spectrometry can identify and quantify over 100,000s
of metabolites, simultaneously. The number of metabolites that can be identified and
quantified depends on the sample preparation x instrument sensitivity x physical concentration
of the metabolite. Subtle differences in expressed genes and proteins can be
verified through metabolomics.
6. HORMONAL PROFILING
In autumn, plants in the field are exposed to multiple stresses that play a role in determining
their capacity to survive the winter. These stresses include low temperatures
(both above and sub-zero), wind, drought, UV, photoinhibition, nutrients, salinity, high
temperatures and mechanical injury. Plants use multiple signaling pathways and signals
to mediate their acclimation responses. Two signaling pathways have been speculated
to regulate cold acclimation (Thomashow, 1999); however, it is the specific combination
of various components of the signaling network coupled with spatial and temporal
factors that ultimately result in an increase in winter hardiness. Low temperature
sensors may be due to changes in membrane fluidity (Murata and Los, 1997), conformational
changes in proteins, altered ABA binding sites, release of sequestered ABA
from plastids, decrease in cell water potential, etc. Secondary signals such as ABA and
second messengers can initiate a cascade of signaling events that may differ from the
critical primary signal. For a comprehensive review on cell signaling the reader is
referred to Xiong et al., (2002). Calcium has been demonstrated to act as a secondary
messenger in low temperature signal transduction during cold acclimation (Monroy
and Dhindsa, 1995). These studies are based on the observation of a transient increase