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

Freezing Stress
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(dehydrin) proteins (Close, 1997), which are induced in response to cold as well as
several other abiotic stresses. Many of these proteins accumulate during CA, and are
hypothesized to interact with membranes and proteins, stabilizing them under desiccation
conditions (Wolkers et al., 2001). Well noted examples include the dehydrins
(DHNs) from barley (Close, 1997), cold responsive (COR) proteins from Arabidopsis
(Gilmour et al., 1992), wheat cold specific (WCS) (Houde et al., 1992) and wheat cold
responsive (WCOR) (Danyluk et al., 1998) from wheat. Another group of proteins that
are induced in response to LT exposure are antioxidant enzymes that are responsible for
scavenging reactive oxygen species produced in response to environmental stress
(Wu et al., 1999). Examples of these types of enzymes include superoxide dismutase
(SOD) (McKersie et al., 1993), ascorbate peroxidase (APX), and glutathione reductase
(Sen Gupta et al., 1993). A method to minimize the number of proteins in a sample, is to
fractionate into sub-samples based typically on a specific chemical characteristic (e.g.
soluble vs. insoluble) or in most cases based on an organelle within the cell (e.g.
ribosome, chloroplast, membrane, etc.). Although the extracellular spaces are not considered
an organelle, a complete proteomic study of the proteins present in this space
has been accomplished (Griffith et al., 1992). Within the extracellular spaces of a plant,
a group of antifreeze proteins (originally isolated from flounder (DeVries, 1971) are
present. These proteins are classified based on their ability to alter the crystal structure
of ice, and inhibiting the formation of secondary ice crystals (Griffith et al., 1992). In
total seven proteins were identified in the apoplastic spaces, with five of them showing
antifreeze properties. Proteins identified in LT exposed plants include some examples
associated with photosynthesis (Gray et al., 1997) and carbohydrate production (Olien
and Clark, 1993), membrane associated proteins (e.g. calcium transport proteins) (Monroy
et al., 1993), and signal transduction proteins (e.g. protein kinases, MAPKs, etc) (Monroy
et al., 1993a). Although the term proteomics is quite novel, the amount of research
conducted on protein accumulation in low temperature tolerant plants is quite significant.
It has been well established that proteins accumulate in response to cold, and that
proteins present in CA plants are well adapted for efficient activity at LT. Due to the
inefficiency of molecular techniques, this is about all we know; with the advent of new
technical techniques like 2D-PAGE, DIGE and MuDPIT we will soon know much more.
5. METABOLIC PROFILING
Major metabolic shifts occur with the development of cold acclimation (Levitt, 1980).
The metabolism of glucose-6-phospate shifts from glycolysis to the pentose pathway
to generate NADPH and nucleic acid precursors (Sagisaka, 1974). Reducing power
utilizing reactions are favoured with the generation of ascorbic acid (Andrews and
Pomeroy, 1978), glutathione (Guy and Carter, 1982) and reduced pyridine nucleotides
(Kacperska, 1985). Adenylate energy charge, ATP, NADPH 2
which are required for
metabolism and repair are elevated during cold acclimation of Brassica leaves
(Kacperska, 1999). Major changes in osmotic potential are related to sugars and sugar