Abstract
The levels of polyamines (PAs), proline (Pro), and γ-aminobutyric acid (GABA) as well as the activity of diamine oxidase (DAO; EC 1.4.3.6) were studied in the roots of 2-day-old lupine (<em>Lupinus luteus</em> L. ‘Juno’) seedlings treated with 200 mM NaCl for 24 h. The effect of adding 1 mM aminoguanidine (AG), an inhibitor of DAO activity, was also analyzed. It was found that in roots of lupine seedlings growing under salt stress, a negative correlation between Pro accumulation and putrescine (Put) content takes place. Pro level increased in roots by about 160% and, at the same time, Put content decreased by about 60%, as a result of ca. twofold increase of DAO activity. The AG added to the seedlings almost totally inhibited the activity of DAO, increased Put accumulation to control level, decreased Pro content by about 25%, and reduced GABA level by about 22%. Addition of 50 mM GABA to the lupine seedlings growing in the presence of AG and NaCl restored Pro content in roots to its level in NaCl-treated plants. In this research, the clear correlation between Put degradation and GABA and Pro accumulation was shown for the first time in the roots of seedlings growing under salt stress. This could be considered as a short-term response of a plant to high salt concentration. Our findings indicate that during intensive Pro accumulation in roots induced by salt stress, the pool of this amino acid is indirectly supported by GABA production as a result of Put degradation.
Highlights
Salt stress is one of the major factors limiting crop production
The present study provides a basis for a better understanding of the role played by PAs in plant response to salt stress, and establishes PA metabolism as an important regulatory mechanism in Pro accumulation
Application of AG to the seedlings growing under salt stress showed a direct link between Put catabolism and Pro and GABA accumulation in roots
Summary
Salt stress is one of the major factors limiting crop production. It causes a wide variety of physiological and biochemical changes in plants. Polyamines (PAs), in combination with proline (Pro) and γ-aminobutyric (GABA), belong to the group of agents with almost universal involvement in a variety of stress responses [1,2,3,4,5]. Accumulation of Pro in stressed plants, up to 100 times to the normal level, has been a well-known fact for more than 40 years [6]. Apart from acting as an osmolyte for osmotic adjustment, proline contributes to stabilizing sub-cellular structures (e.g., membranes and proteins), scavenging free radicals, and buffering cellular redox potential under stress conditions [3,7]. Pro itself may serve as a nitrogen and carbon source needed in stress recovery [8,9]
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