Chemistry Reference
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Table 2 Qualitative assay of specific lignin staining with phloroglucinol in the basal part of
roots of 5-day-old wheat seedlings pre-treated with 50 lM SA during 24 h in the presence or
absence of 5 mg/l fluridone and then 24 h after exposure of seedlings on 1 mM cadmium acetate
Variant 5-day-old
Control -
1 mM cadmium acetate +
(SA) ? cadmium acetate ++
(FL ? SA) ? cadmium acetate -/+
'' -''indicates absence of staining, ''-/+'' very weak staining, number of ''+'' reflects the extent
of staining intensity, ''++'' being very strong staining
transient activation of antioxidant enzymes in wheat seedlings (Fig.
3
) involved in
neutralization of oxidative stress-induced burst.
An additional argument in support of involvement of ABA in the regulation of
SA-induced protective reactions reducing the damaging effect of cadmium stress on
wheat plants is in the data showing significant decline in lignin accumulation in the
cell walls of the basal part of seedling roots pretreated with the mixture of fluridone
with SA (Table
2
). This is likely to be due to prevention by fluridone of the SA-
induced production of H
2
O
2
and activation of the key enzymes of lignin biosyn-
thesis (PAL and peroxidase) being under the control of ABA (Moura et al.
2010
).
Since, as noted above, pretreatment with SA reduced the extent of the damaging
effect of cadmium on the growth processes of wheat seedlings, one would expect
that the manifestation of the protective effect of SA on the plants under cadmium
stress is due to the increased barrier properties of the cell walls of roots bringing
about the inhibition of the entry of toxic ions into the root tissues and their
subsequent delivery to the shoot.
Thus, the histochemical analysis with the help of dithizone reagent (Seregin and
Ivanov
1997
) revealed the presence of cadmium in all tissues of the transverse
sections of roots of 5 days-old wheat seedlings untreated with SA (Table
3
). At the
same time in the experiments with SA-pre-treatment cadmium was detected only
in rhizoderm and outer layers of the primary cortex (Table
3
). These data dem-
onstrate the important contribution of SA-induced acceleration of lignin deposition
in the basal part of seedlings roots and additional intensification of the process
Table 3 The effect of pretreatment of 3-day-seedlings with 50 lM SA or initially with 5 mg/l
fluridone alone during 3 h and then with the mixture of fluridone with SA for 24 h on cadmium
ion distribution over root tissues of 5-day-old wheat seedlings
Treatment
Tissue
Rhizodermis
Primary
cortex
Endodermis
Pery
cycle
Stellar
parenchyma
Conducting
tissues
Control
-
-
-
-
-
-
Cd acetate,
1 mM, 24 h
+
+
+
+
+
+
(SA) ? Cd
++
-
-
-
-
-
(FL ? SA) ? Cd
+
+
+
+
+
+
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