چکیده
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Salinity constitutes one of the most important causes leading to severe reduction in
plant yield. Several reports correlate the accumulation of polyamines in plants with tolerance to
abiotic stress cues. The present study examined three Medicago truncatula genotypes with differing
sensitivities to salinity (TN1.11, tolerant; Jemalong A17, moderately sensitive; TN6.18, sensitive),
with the aim of examining the genotype-specific involvement of the polyamine metabolic pathway
in plant response to salinity. The study was carried out with leaves harvested 48 h after watering
plants with 200 mM NaCl. A comprehensive profile of free polyamines was determined using high
performance liquid chromatography. All genotypes showed spermidine and spermine as the most
abundant polyamines under control conditions. In salinity conditions, spermine levels increased at
the expense of putrescine and spermidine, indicating a drift of polyamine metabolism towards the
synthesis of increasing polycationic forms as a stress response. The increasing balance between high
and low polycationic forms was clearly diminished in the salt-sensitive genotype TN6.18, showing a
clear correlation with its sensitive phenotype. The polyamine metabolic profile was then supported
by molecular evidence through the examination of polyamine metabolism transcript levels by RTqPCR.
General suppression of genes that are involved upstream in the PA biosynthetic pathway
was determined. Contrarily, an induction in the expression of genes involved in the biosynthesis
of spermine and spermidine was observed, in agreement with the metabolic analysis. A significant
induction in diamino oxidase expression, involved in the catabolism of putrescine, was specifically
found in the sensitive genotype TN6.18, indicating a distinct metabolic response to stress. Present
findings highlight the involvement of polyamines in the defense response of Medicago genotypes
showing sensitivity to salt stress.
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