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The treatment was able to reverse the preferential allocation of
14
C in the first-order tiller, and
the near-complete neglect of the side tillers, in drought-stressed plants (Bergmann et al. 1991;
Eckert 1988). The consequences are once more depicted in Figure 4. Significant gains in the
dry weight were restricted to the whole fertile side tillers in wheat and to grains from these
second-order tillers in rye. Both organs showed also higher concentrations in total nitrogen
(Bergmann et al. 1991), although the N content in main-tiller grains did not decline.
Treatment with EA improved thus the acquisition of soil nitrogen.
Table 2. Changes in the content of organic N and the stress metabolite, glycine betaine,
in pre-mature grains of spring barley, resulting from drought stress and treatment with
ethanolamine
Crude protein
a
Lysine
b
Isoleucine
b
Proline
c
Glycine betaine
c
Stress
intensity
Cultivar
Untr
EA
Untr
EA
Untr
EA
Untr
EA
Untr
EA
Low
Alexis
6.68
7.59
e
234
239
238
255
10.2
26.5
d
6.9
9.7
e
Krona
7.45
6.82
213
201
212
210
1.0
1.0
9.0
7.9
3.02
d
86
d
92
d
60.9
f
20.0
d
9.6
f
7.5
d
High
Alexis
2.38
59
63
Krona
1.80
2.35
d
40
63
d
46
69
d
1.4
1.3
9.1
5.2
d
a
Content in g per pot;
b
content in mg per pot;
c
content in µmol/g dry matter.
d
Values of the EA treatment significantly (
p
< 0.05) different from those of the untreated (Untr)
control.
e
Values of the EA treatment significantly (
p
< 0.1) different from those of the untreated control.
f
High-stress values significantly different (
p
< 0.05) from the respective low-stress values.
Plants of the stress-susceptible
cv
. Alexis and the resistant
cv
. Krona cultured in Mitscherlich pots (6.9
kg rooting soil). Adapted from Bergmann et al. (2002).
In the spring barley cultivars Alexis and Krona, premature-grain concentrations in crude
protein and in the amino acids, lysine and isoleucine were identical under low-stress
conditions, and their losses under high-stress conditions were also of the same order (Table 2;
Bergmann et al. 2002). Due to the ameliorating effect of EA, organic-N concentrations
reduced by stress increased to 130 to 150 %. Synchronously, the amino acid composition of
the grain protein was re-adapted to that of grains from non-stressed plants (Leinhos and
Bergmann 1995a; b; Leinhos et al. 1996).
Concentrations of free proline in untreated shoot tissue of Alexis and Krona determined
at early flowering increased to the 2.4/3.9-fold and reached identical levels in both cultivars
when drought stress conditions changed from low to high (Bergmann et al. 2002; data not
shown). In pre-mature grains of
cv
. Krona analyzed at 10 wk after treatment with EA, proline
concentrations were uniformly low, irrespective of the stress conditions (Table 2). Grains of
cv. Alexis retained their high stress-induced proline concentration in the untreated control but
lost their proline content widely after EA treatment. Concentrations in free proline did
apparently not confer the grain-yield determining stress tolerance to barley (compare Figure 2
and Table 2). This came also true for glycine betaine. It has been suggested that proline
formation expresses the degree of injury to plant tissue (Hanson and Nelsen 1978). This
osmoprotectant could primarily serve as C and N resource of the recovering plant (Hare and
Cress 1997). Proline could also play a vital role in maintaining integrity of plasma
membranes and could act as signalling molecule in response to abiotic stresses (Kishor et al.
2005; Siripornadulsil et al. 2002; Su and Wu 2004).
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