STABILIZING PRODUCTIVITY OF DROUGHTSTRESSED CROPS BY FOLIAR APPLICATION OF ALKANOLAMINES - Soybean and Wheat Crops: Growth, Fertilization, and Yield - page 226

increasing pool in linolenic acid (Figure 1; Bergmann et al. 1999; Zuniga et al. 1990). The
concentration of free amino acids increases by de-novo synthesis and the lysis of membrane

STRESS
Cytoplasmic dehydration

Changes in proteome, proteolysis,
less protein and more free amino
acid synthesis

Osmoprot-
ectants

Declining
photosynthesis

Cell membranes:
Glycerophospholipids

Proteins

Glutamate

Phenylalanine

Reactive
oxygen
species
Radical
scavengers,
antioxidative
enzymes

Proline

Serine

Serine,
ethanolamine,
choline

Cinnamic acid

Arginine

Ethanolamine

Hydroxycinn-
amic acid

Glycine
betaine

Putrescine

Accumulation
of nitrate

Choline

Aminocyclopro-
pane carboxylic
acid

Lipid
peroxidation

Phenols, phen-
ylpropanoids,
flavonoids

Glycine
betaine

Fatty acids

Linolenic
acid

Ethylene

Tannins
Lignins

Polyamines

Jasmonate Aldehydes

Figure 1. Some drought-stress induced events in plants (refer to Section 1).

proteins. Free serine is then decarboxylated to form the major quantities of EA (Bergmann
1996; Rontein et al. 2003). Phenylalanine is transformed to phenolic radical scavengers,
whereas glutamate plays a role as precursor of proline and the polyamines, putrescine,
spermidine, and spermine which accumulate in the cell. Polyamines are radical scavengers
and inhibitors of lipid peroxidation (Benavides et al. 2000; Chang and Kao 1997; Borrell et
al. 1997). They are thus involved in structural and functional stabilization of cell membranes
and organelles under stress. Long-term responses make plants adapted, and to some degree
resistant to detrimental influences of stressors (see Bartosz 1997; Bergmann et al. 1999;
Chernyad'ev 2005; Rajam et al. 1998 for more details).
Among stress metabolites of interest, the alkanolamines, EA and choline and their
phosphatidyl derivatives are attached to the polar phosphorus moiety which heads the
glycerol backbone of the phospholipid molecule (Keith Cowan 2006). They are constituents
of membrane lipids in all taxa of the plant kingdom (Fritsche 1990; Galliard and Mercer
1985; Incharoensakdi and Wutipraditkul 1999) and are also found water-soluble at 5 to 50
ppm in fresh plant tissue (Bergmann 1996). The diamine, putrescine, and the polyamines,
spermidine and spermine are common to eukaryotic plants but not to several algae (Smith
1985; Tiburcio et al. 1990). The alkanolamines (Kamalyan 1971; Kamisaka 1979) and
glycine betaine as their end product (Ashraf et al. 2008; Bergmann and Eckert 1984; Mäkelä
et al 1996), but also the di- and polyamines (Galston 1983; Smith 1985) were found to be
conducive to growth and metabolism of crop plants and protecting from damage by stress
(Bergmann et al. 1983; 1991; 1999; Fujii et al. 1972; Mascher et al. 2005).
Monoethanolamine (Davtyan 1981; Fujii et al. 1972; Ishigami and Suzuki 1970; Kamalyan
1971; Washio and Kiguchi 1972) and phenylethanolamine (Kamisaka 1979; Oota 1974) were