Agriculture Reference
In-Depth Information
temperate climatic conditions of Central Europe, the ecotoxicologically unobjectionable
treatment has not yet become part of daily agricultural practice. In the light of the world-
wide food crisis, an application of stress control agents could help stabilize crop
production in semi-arid and saline regions and during temporary rainfall deficits. The
treatment should also revalorize the economic role of the multitude of traditional cereal
cultivars in use which are adapted to the local soil and climate conditions.
1.
P
LANT
R
ESPONSE TO
A
BIOTIC
S
TRESS
Adverse environmental conditions such as drought, heat, salinity, heavy-metal
contamination, waterlogging, soil acidity, soil compaction, and chill exert injurious strain to
plants and match therefore the definition of abiotic stress factors (Levitt 1980). Some of the
short-term plant responses to stress are also incited by pathogen ingress, arbuscular-
mycorrhiza formation, and even by exposure to IAA releasing soil bacteria (Bergmann et al.
1999; Kemp and Burden 1986; Leinhos and Bergmann 1995a).
Freezing, desiccation, and salinity go along with cytoplasmic dehydration (McKersie
1991) and changes in the concentration of numerous proteins (Caruso et al. 2008) and
enzymatic activities. Dehydration triggers the formation of sugars, polyols, amino acids and
their derivatives, including proline, N-dimethylproline, trigonelline, glycine betaine, and
polyamines (Bergmann et al. 2001; Blum 1996; McNeil et al. 1999; Mullet and Whitsitt
1996; Schlee 1992) with osmoprotective properties (Blum 1996; Morgan 1991; 1995; Rajam
et al. 1998). The synchronously appearing radicals and reactive oxygen species (Baker and
Orlandi 1995; Lamb and Dixon 1997; Larson 1997) which are by-product of the aerobic
metabolism (Bartosz 1997) and are increasingly formed in chloroplasts by inhibition of
photosynthesis (Dat et al. 2000; Loggini et al. 1999; Smirnoff 1998) impair permeability and
structure of cellular plasma, mitochondrial, and thylakoid membranes (Bewley 1979; Mascher
et al. 2005; McKersie 1991; Santarius et al. 1979).
In short-term responses, stress-resistant plants neutralize reactive oxygen species with the
antioxidative enzymes, superoxide dismutase, peroxidase, catalase, and glutathione reductase
(McKersie 1991; Mascher et al. 2005) but also with radical scavengers such as glutathione,
ascorbate, phenolics, amines, and terpenoids (Bartosz 1997; Elstner et al. 1994; Larson 1997;
Marschner 1995).
In long-term plant responses to stress, the destructive action of enzymes and reactive
oxygen species to protein and phospholipid component of cell membranes results in
proteolysis and in the formation of fatty acid and amino acid derivatives, respectively (Figure
1). Activated phospholipases and esterases catalyze the release of ethanolamine (EA),
choline, serine, or their phosphate esters as well as fatty acids from the membranes'
phospholipid molecule (Bergmann 1996; Giddings Jr. and Hanson 1982; Keith Cowan 2006;
Krishanquamurthy and Bhagwat 1990). The alkanolamines, EA and choline, or their
phosphoryl- and phosphatidyl derivatives are finally transformed to the inert, osmoprotective
glycine betaine (Bergmann et al. 2002; Eckert et al. 1988b; Hanson et al. 1979). Fatty acids
are peroxidized by the reactive oxygen species (Bowler et al. 1992; Dat et al. 2000; Hartley-
Whitaker et al. 2001) to accumulate with aldehydes and the proteinase inhibitor and
phytohormone, jasmonate, which is catalyzed by lipoxygenase (Ryan 1992) from the
Search WWH ::
Custom Search