Modulation of Cu 2+ accumulation by (aminoethoxyvinyl)glycine and methylglyoxal bis (guanylhydrazone), the inhibitors of stress ethylene and polyamine synthesis in wheat genotypes
The effectiveness of Cu 2+ accumulation was investigated in three wheat cultivars with different copper sensitivity (Triticum aestivum cv. GK Tiszatáj, GK Kata and GK Öthalom). Supraoptimal Cu 2+ concentrations result in toxicity symptoms in the sensitive genotype and increase the production of the stress hormone, ethylene both in the leaves and root tissues of wheat seedlings. The sensitive cultivar, cv. Öthalom produced less ethylene than the tolerant genotypes (cvs Tiszatáj and Kata) in the roots whether the ethylene measurements were done over the 6-h period after Cu 2+ exposure. Levels of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, did not change characteristically during this period in either the tolerant or sensitive seedlings. The biosynthesis of ethylene has a common intermediate, S-adenosylmethionine (SAM) with the synthesis of the polyamine spermidine and 2-deoxymugineic acid, a Fe 3+ -solubilizing and transporting wheat phytosiderophore. These chelating substances also mediate the transport of different bivalent cations, such as Cu 2+. The biosynthetic pathways of ethylene and polyamines, spermidine and spermine may compete for SAM with the phytosiderophore synthesis. Simultaneous inhibition of SAM decarboxylase by 0.5 M methylglyoxal bis (guanylhydrazone) (MGBG), and 1-aminocyclopropane-1-carboxylic acid synthase by 10 μM (2-aminoethoxy-vinyl)glycine (AVG), significantly increased the Cu 2+ accumulation in root tissues of the wheat cultivars independently of their sensitivities. MGBG alone resulted in an enhanced copper content but AVG proved to be ineffective. This suggests that the amount of SAM allocated for polyamine formation may limit the phytosiderophore synthesis or spermidine (spermine) in itself may control the uptake of Cu 2+.
Key words(2-aminoethoxyvinyl)glycine copper accumulation ethylene production methylglyoxal bis (guanylhydrazone) phytosiderophores spermidine synthesis
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