Authors:Irma Tari, Jolán Csiszár, Katalin Gémes and Ágnes Szepesi
The effectiveness of Cu
accumulation was investigated in three wheat cultivars with different copper sensitivity (
cv. GK Tiszatáj, GK Kata and GK Öthalom). Supraoptimal Cu
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
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
-solubilizing and transporting wheat phytosiderophore. These chelating substances also mediate the transport of different bivalent cations, such as Cu
. 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
(guanylhydrazone) (MGBG), and 1-aminocyclopropane-1-carboxylic acid synthase by 10 μM (2-aminoethoxy-vinyl)glycine (AVG), significantly increased the Cu
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
Authors:Judit Kovács, Péter Poór, Ágnes Szepesi and Irma Tari
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.
Authors:Irma Tari, Adrienn Guóth, D. Benyó, Judit Kovács, P. Poór and B. Wodala
The effects of PEG 6000-induced osmotic stress (−0.976 MPa) on the root growth of young plants, and the changes in abscisic acid (ABA), reactive oxygen species (ROS) and NO contents were investigated in the root tips of a drought-tolerant and a drought-sensitive wheat cultivar (Triticum aestivum L. cvs. MV Emese and GK Élet, respectively). The root length of cv. MV Emese was more effectively reduced than that of GK Élet by osmotic stress. Concomitantly, the ABA content of the 15-mm apical zone of the roots remained at the control level in GK Élet cultivar, but in MV Emese it decreased significantly after the early phase of the experiment, indicating that the accumulation of ABA is necessary for the maintenance of root growth under osmotic stress. The extent of ROS accumulation relative to the respective control was more pronounced in the elongation zone of roots in MV Emese in the later stages of the experiment, while NO concentrations increased significantly early after PEG exposure, suggesting that high concentrations of ROS and NO were unfavourable for root expansion. In contrast, in cv. Élet, the high NO content in the elongation zone declined to the control level under osmotic stress within 4 days. The changes in root growth due to osmotic stress did not exhibit a correlation with the drought tolerance of the genotypes defined on the basis of the crop yield.
Authors:P. Poór, P. Borbély, Judit Kovács, Anita Papp, Ágnes Szepesi, Z. Takács and Irma Tari
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.
Authors:Edit Horváth, Krisztina Bela, Csaba Papdi, Ágnes Gallé, László Szabados, Irma Tari and Jolán Csiszár
Arabidopsis thaliana contains 54 soluble glutathione transferases (GSTs, EC 18.104.22.168), which are thought to play major roles in oxidative stress responses, but little is known about the function of individual isoenzymes. The role of AtGST phi 9 (GSTF9) in the salt- and salicylic acid response was investigated using 2-week-old Atgstf9 and wild type (Wt) plants. Atgstf9 mutants accumulated more ascorbic acid (AsA) and glutathione (GSH) and had decreased glutathione peroxidase (GPOX) activity under control conditions. Treatment of 2-week-old seedlings with 10−7 M salicylic acid (SA) for 48 h resulted in elevated H2O2 level and enhanced GST activity in Atgstf9 plants, 10−5 M SA treatment enhanced the malondialdehyde and dehydroascorbate contents compared to Wt. 50 and 150 mM NaCl increased the GST activity, AsA and GSH accumulation in Atgstf9 seedlings more pronounced than in Wt plants. We found that the Atgstf9 mutants had altered redox homeostasis under control and stress conditions, in which elevated AsA and GSH levels and modified GST and GPOX activities may play significant role. The half-cell potential values calculated from the concentration of GSH and GSSG indicate that this GST isoenzyme has an important role in the salt stress response.
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.