Mechanisms of salt stress tolerance development in barley plants under the influence of 5-aminolevulinic acid |
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Authors: | N G Averina E R Gritskevich I V Vershilovskaya A V Usatov E B Yaronskaya |
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Institution: | 1.Institute of Biophysics and Cell Engineering,National Academy of Sciences of Belarus,Minsk,Belarus;2.Research Institute of Biology,Southern Federal University,Rostov-on-Don,Russia |
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Abstract: | Growing barley (Hordeum vulgare L.) plants for 7 days on NaCl solutions (20–200 mM) decreased chlorophyll (Chl) a and b content with respect to that in untreated control plants. The content of free proline and the plant ability to synthesize
5-aminolevulinic acid (ALA) started to increase in parallel at salt concentrations of 20–50 mM. The maximum amount of ALA
accumulated in plants grown at 100 mM NaCl was twofold higher than in control plants grown on fresh water. In this case the
proline content increased 2.8-fold. On further increase in salt concentration, the rate of ALA accumulation decreased, approaching
control values at 150 mM NaCl; even lower rates were observed at 200 mM NaCl. The reduced ability to synthesize ALA was accompanied
by an increase in proline content. The albino tissue of plants treated at the seed stage with the antibiotic streptomycin
lost its ability to synthesize ALA needed for Chl formation. The proline content in the albino tissue was tenfold higher than
in control green plants and was 30-fold higher when the plants were grown on solutions with 100 mM NaCl. No effect of NaCl
on ALA-dehydratase activity was noted. As NaCl concentration was raised, there occurred the decrease in magnesium chelatase
activity, accumulation of reactive oxygen species (ROS), the increase in ascorbate peroxidase activity, and a slight decrease
in lipid peroxidation level. Growing plants in the presence of 150 mM NaCl and 10 or 60 mg/l exogenous ALA led to the increase
in proline content (by a factor of 1.8 and 4.2, respectively) and to the decrease in ROS content, in comparison with plants
grown on salt solutions without ALA. Furthermore, in the presence of exogenous ALA, the parameters of seedling growth became
similar to those of NaCl-untreated plants. The role of ALA in plants as an antistress agent is considered. ALA is supposed
to confer tolerance to salt stress by taking part in Chl and heme biosynthesis and also through functioning as a plant growth
regulator. A hypothesis is put forward that the impairment of ALA-synthesizing ability may redirect metabolic conversions
of glutamic acid from Chl and heme synthesis to the proline synthesis pathway, which would stimulate proline biosynthesis
and improve salt tolerance. |
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