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  • Author or Editor: Ágnes Szepesi x
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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+ .

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The hypersensitive response (HR), a type of programmed cell death (PCD) during biotic stress is mediated by salicylic acid (SA). The aim of this work was to reveal the role of proteolysis and cysteine proteases in the execution of PCD in response of SA. Tomato plants were treated with sublethal (0.1 mM) and lethal (1 mM) SA concentrations through the root system. Treatment with 1 mM SA increased the electrolyte leakage and proteolytic activity and reduced the total protein content of roots after 6 h, while the proteolytic activity did not change in the leaves and in plants exposed to 0.1 mM SA. The expression of the papain-type cysteine protease SlCYP1, the vacuolar processing enzyme SlVPE1 and the tomato metacaspase SlMCA1 was induced within the first three hours in the leaves and after 0.5 h in the roots in the presence of 1 mM SA but the transcript levels did not increase significantly at sublethal SA. The Bax inhibitor-1 (SlBI-1), an antiapoptotic gene was over-expressed in the roots after SA treatments and it proved to be transient in the presence of sublethal SA. Protease inhibitors, SlPI2 and SlLTC were upregulated in the roots by sublethal SA but their expression remained low at 1 mM SA concentration. It is concluded that in contrast to leaves the SA-induced PCD is associated with increased proteolytic activity in the root tissues resulting from a fast up-regulation of specific cysteine proteases and down-regulation of protease inhibitors.

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The plant hormone ethylene or the gaseous signalling molecule nitric oxide (NO) may enhance salt stress tolerance by maintaining ion homeostasis, first of all K+/Na+ ratio of tissues. Ethylene and NO accumulation increased in the root apices and suspension culture cells of tomato at sublethal salt stress caused by 100 mM NaCl, however, the induction phase of programmed cell death (PCD) was different at lethal salt concentration. The production of ethylene by root apices and the accumulation of NO in the cells of suspension culture did not increase during the initiation of PCD after 250 mM NaCl treatment. Moreover, cells in suspension culture accumulated higher amount of reactive oxygen species which, along with NO deficiency contributed to cell death induction. The absence of ethylene in the apical root segments and the absence of NO accumulation in the cell suspension resulted in similar ion disequilibrium, namely K+/Na+ ratio of 1.41 ± 0.1 and 1.68 ± 0.3 in intact plant tissues and suspension culture cells, respectively that was not tolerated by tomato.

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Acta Biologica Hungarica
Authors: Irma Tari, D. Camen, Giancarla Coradini, Jolán Csiszár, Erika Fediuc, Katalin Gémes, A. Lazar, E. Madosa, Sorina Mihacea, P. Poor, Simona Postelnicu, Mihaela Staicu, Ágnes Szepesi, G. Nedelea and L. Erdei

Drought resistance of bean landraces was compared in order to select genotypes with either high morphological or high biochemical-physiological plasticity. The lines in the former group exhibited fast reduction in fresh and dry mass, decreased the water potential in primary leaves after irrigation withdrawal and the biomass mobilized from the senescent primary leaves was allocated into the roots. These genotypes had high frequency of primary leaf abscission under water stress. The genotypes with plasticity at the biochemical level maintained high water potential and photochemical efficiency, i.e. effective quantum yield, high photochemical (qP) and low non-hotochemical (NPQ) quenching in primary leaves under drought stress. While superoxide dismutase activity was not influenced by the drought and the genotype, catalase activity increased significantly in the primary leaves of the genotypes with efficient biochemical adaptation. Lines with high morphological plasticity exhibited higher quaiacol peroxidase activity under drought. Proline may accumulate in both cases, thus it may be a symptom of protein degradation or a successful osmotic adaptation. On the basis of contrasting responses, the genetic material cannot be screened for a large-scale breeding program by a single physiological parameter but by a set of the methods presented in this work.

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