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Volume 2 Number 2 2008 
CONTENTS AND ABSTRACTS
Nina V. Chichkova, Raisa A. Galiullina (Russia), Michael E. Taliansky (UK), Andrey B. Vartapetian (Russia) Tissue Disruption Activates a Plant Caspase-Like Protease with TATD Cleavage Specificity (pp 89-95)
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ABSTRACT
Original Research Paper: Recently, several caspase-like proteases have been described in plants. In particular, we have identified a tobacco caspase-like protease (CLP) that has a caspase cleavage specificity, that becomes activated in the course of plant programmed cell death (PCD), and that is essential for implementation of the cell death programme. The enzyme cleaves a peptide bond next to the Asp (D) residue within the TATD motif in the substrate VirD2 protein. Here we found that activation of tobacco CLP does occur in the course of healthy leaf tissue disruption as well, possibly through zymogen activation or enzyme de-sequestration. CLPs with identical cleavage specificity were demonstrated to be ubiquitous in mono- and dicotyledonous plants. Purified CLPs of tobacco and rice were shown to possess similar biochemical properties. Furthermore, inhibitor analysis demonstrated that CLP is sensitive to a number of peptide aldehyde inhibitors of animal caspases, with a notable exception of DEVD-CHO. Since these inhibitors have previously been employed in suppression of PCD mediated by different stress inducers, this result suggests that their inhibitory effect could be due, at least in part, to inactivation of the CLP under study.
Eloísa Hernández-Lucero (Mexico), Oscar A. Ruiz (Argentina), Juan Francisco Jiménez-Bremont (Mexico) Effect of Salt Stress on Polyamine Metabolism in Two Bean Cultivars (pp 96-102)
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ABSTRACT
Original Research Paper: In agricultural areas, salinity affects plant growth, development and productivity, causing loss of economically important crops. Nitrogen-derived compounds such as polyamines (PAs) are differentially accumulated in diverse plants species in response to salinity. PA and chlorophyll (Chl) contents, as well as water potential (Ψw), were assessed in leaves of two common bean cultivars subjected to salt stress for one and seven days; these bean cultivars, ‘Pinto Villa’ and ‘Canario 60’, differ in their drought tolerance phenotype. Salt stress induced a phenotypic behaviour similar to that of drought in which the sensitive ‘Canario 60’ showed a pronounced decrease in Ψw, in comparison to the tolerant ‘Pinto Villa’. Regarding PAs, after the first day of treatment, the levels of all of them (putrescine (Put), spermidine (Spd) and spermine (Spm)) increased in tolerant cultivar (‘Pinto Villa’) while in the sensitive one (‘Canario 60’) the levels of Spd and Spm only increased at 400 mM NaCl. At the seventh day, the tolerant cultivar showed an accumulation of Spm at the higher concentrations of NaCl used (150 and 400 mM), whereas a decrease in PA content occurred in the sensitive cultivar at all concentrations assayed. Furthermore, the effect of salt stress on the expression of the main genes involved in PA biosynthesis, including a new S-adenosylmethionine decarboxylase (SAMDC) gene identified in this work, was analysed. It is suggested that Spm accumulation in ‘Pinto Villa’ might be part of the mechanism conferring salt tolerance.
Taek-Ryoun Kwon (South Korea), Zamin Shaheed Siddiqui (Pakistan), Phil J. C. Harris (UK) Physiological Variation of Brassica Cultivars/Landraces during Seed Germination and Early Seedling Growth under Salt Stress (pp 103-109)
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ABSTRACT
Original Research Paper: Physiological variations of fifteen Brassica juncea cultivars/landraces and a Brassica rapa landrace during germination and early seedling growth under salt stress were investigated. Percent germination, rate, vigour and threshold were evaluated. Salinity decreased the percent germination, rate, and vigour of two Brassica species, with considerable variation among cultivars/landraces. Relatively high thresholds, between 300 to 250 mM NaCl for inhibition of total germination were observed in B. juncea cultivars of Indian origin i.e. RH 30, RH 8606, RH 9021, RH 9011 and Prakash. The lowest thresholds were recorded in Common green, Ndakupuka and Sani. From the germination study, a relatively salt-tolerant B. juncea cv. Prakash, two B. juncea landraces Common green and Ndakupuka and a relatively salt-sensitive B. rapa landrace Sani were selected for salinity tolerance assessment at the seedling stage. The growth of Common green, Ndakupuka, Prakash, and Sani was retarded with increasing salinity reducing the leaf area of all tested cultivars. Salinity caused an accumulation of Na+ ions and a decrease of K+, Ca++, and Mg++ ions in the shoots of the tested cultivars. Na+ accumulation was highest in Sani and lowest in common green at 175 mM NaCl. The K+ content of the shoots in Sani was lowest in treated and control samples. Likewise, the Ca++ content of shoots of Sani seedlings treated with NaCl was low but higher than Common green. The effect of NaCl on Mg++ was similar to that on Ca++. The results suggest that the higher relative growth reduction of Sani may be correlated with higher Na+ accumulation and lower K+, Ca++ and Mg++ uptake under a saline environment. A physiological explanation is provided for salt stress tolerance in all tested cultivars and landraces.
Majid Jami Al-Ahmadi, Mohammad Kafi (Iran) Water Relations of Kochia (Kochia scoparia (L.) Schrad) under Different Salinities of Irrigation Water (p 110-112)
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Short Communication: In order to estimate kochia (Kochia scoparia) water use efficiency (WUE), an experiment was performed in Birjand, a dry and saline area in South Khorasan, Iran, by using irrigation water of three different salinity levels, i.e. 1.5, 8.6, and 28.2 dSm-1. Several measurements were conducted during the growth season to determine radiation fraction passed through canopy and leaf area index, thereby ground cover percentage was calculated. Reference crop evapotranspiration calculated using Hargreave’s method, corrected by FAO, and after drawing crop coefficient curves, crop evapotranspiration was determined. Ultimately, crop WUE in different salinity levels was calculated for forage and seed yields. Evaluation of crop coefficient curves showed that salinity caused a delay in initial season growth and forced plant maturity in late season. The mean crop evapotranspiration between salinity treatments was equal to 915 mm. WUE was affected by salinity, more than by evapotranspiration, showing biomass production is more sensitive to salinity than crop evapotranspiration. For forage yield, salinity enhancement from 1.5 to 8.6 dSm-1 caused WUE to be increased slightly from 11.5 to 11.9 kg ha-1 per each mm evapotranspiration, though at higher levels of salinity it decreased to 7.6 kg ha-1 per each mm evapotranspiration. WUE for seed yield in 1.5, 8.6, and 28.2 dSm-1 were 2.92, 2.42, and 2.44 kg ha-1 per each mm evapotranspiration, respectively. As forage use is the main purpose of kochia production, it seems that its biomass production have a high tolerance to water and soil salinity.
Suping Zhou, Roger Sauvé, Braden Boone, Shawn Levy (USA) Identification of Genes Associated with Aluminum Toxicity in Tomato Roots Using cDNA Microarrays (p 113-120)
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Original Research Paper: cDNA microarrays (Tom 1) were used to analyze changes in transcript accumulation in tomato (Solanum lycopersicum 'Money Maker') roots grown in liquid cultures containing 20 μM AlK(SO4)2. Out of 1,362 genes that had significant changes in transcript accumulation (FDR<0.05), 569 were reduced and 793 were induced. The down-regulated genes included those found in the cell cycle progression (p34cdc2 protein kinase, cyclin, and histone), putrescine synthesis, ABC transporter and germin-like protein. Genes that were induced by Al included glutamate synthase, pectin modification, histidine synthesis, proline synthesis, metallothionein-like protein, multidrug efflux proteins (MATE), ethylene biosynthesis and detoxification proteins. Different isoforms of V-ATPase, glutathione transferases and others in the multiple gene families were either induced or repressed. Wide arrays of genes that regulate transcription and translation activities, as well as signal transduction, were also affected.
Przemysław Malec, Andrzej Waloszek (Poland), M. N. V. Prasad (India), Kazimierz Strzałka (Poland) Zinc Reversal of Cadmium-induced Energy Transfer Changes in Photosystem II of Ceratophyllum demersum L. as Observed by Whole-leaf 77K Fluorescence (pp 121-126)
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ABSTRACT
Original Research Paper: We have examined the mode of interaction between cadmium (Cd) and zinc (Zn), toxic and micronutrient elements, on the photosynthetic apparatus, with respect to energy transfer in leaves of the free-floating macrophyte Ceratophyllum demersum L. Low temperature fluorescence spectroscopy enabled in situ detection of changes in energy transfer from pigments energetically coupled to PS I and PS II, induced by Cd and Zn in C. demersum. The two-point normalization algorithm permitted a direct comparison of the shape of excitation spectra in the wavelength range including absorption maxima of main photosynthetic pigments (from 438 to 555 nm). The results indicate that Cd and Zn in concentrations up to 1000 μM can induce remarkable changes in energy transfer from carotenoids to reaction centers of PS II and antenna complexes LHC II in C. demersum leaves. Cd at 1000 μM, after 48 hr incubation, induced the most pronounced increase of fluorescence from PS II/LHC II, attributable to excitation of the carotenoid pool (482 and 486 nm bands). The presence of Zn (100 μM) together with Cd (1000 μM) suppressed the observed increase of carotenoid contribution to energy transfer to photosynthetic reaction centers in PS II/LHC II. The changes in the contribution of carotenoids to energy transfer, as observed by low-temperature fluorescence spectroscopy show no direct correlation with relative changes in concentrations of these pigments in untreated versus metal-treated C. demersum, as measured by HPLC. In conclusion, the presence of Zn in the environment may prevent effects on photosynthetic energy transfer, induced by high concentrations of Cd in PS II/LHC II of aquatic plants.
Nitika Arora, Renu Bhardwaj, Priyanka Sharma, Hardesh Kumar Arora (India) Mitigation of Cu Toxicity by 28-homobrassinolide in Zea mays L. (pp 127-130)
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Original Research Paper: The effects of 28-homobrassinolide (28-homoBL) on lipid peroxidation and antioxidative enzyme activities in the Zea mays L. (var. Partap-1) seedlings exposed to copper (Cu) were studied. The surface-sterilized seeds of Z. mays were treated with different concentrations of Cu (0.5, 1.0, 1.5 and 2.0 mM) alone or in combination with 28-homoBL (10-4, 10-6 and 10-8 mM) for 7 days. The activities of antioxidative enzymes (superoxide dismutase (EC 1.15.1.1), catalase (EC 1.11.1.6), ascorbate peroxidase (EC 1.11.1.11), guaiacol peroxidase (EC 1.11.1.7) and glutathione reductase (EC 1.6.4.2)), protein and malondialdehyde (MDA) content were analyzed in 7-days-old seedlings. The activities of superoxide dismutase and guaiacol peroxide were enhanced whereas the activities of other enzymes declined with an increase in the concentration of Cu alone. However the 28-homoBL treatments further stimulated the activities of all antioxidative enzymes. The level of MDA content decreased under brassinoloide treatments but increased under the influence of metal treatments.
Ahmed Mansour (Egypt) Heat ShockActivationof Phospholipase C Signaling Pathway in TobaccoCells (pp 131-137)
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ABSTRACT
Original Research Paper: Phospholipid signaling, frequently associated with rapid responses to environmental stimuli, is well known in animal and some higher plants. Heat shock is a major component of abiotic stress and stimulates many signaling pathways. Applying heat shock stress to tobacco (Nicotiana tabacum) BY-2 cells activated the phospholipids signaling pathway, including protein kinase C (PKC) and diacylglycerol (DAG) kinase pathways, both of which are associated with the downstream phospholipid pathway. In addition, activation of phospholipase C (PLC) activated heat-activated MAP kinase (HAMK) and caused the accumulation of heat shock protein 70 (HSP70) as an end-point marker. In contrast, chemical inhibition of PLC, PKC or DAG kinase completely or partially inhibited HAMK activation and HSP70 accumulation during heat shock. Moreover, treatment of cells with phosphatidic acid (PA) or PKC activators led to HAMK activation and HSP70 accumulation at 25°C, as did treatment of cells with either IP3 or cADPR, both of which are known to release Ca2+ from intracellular stores. We conclude that the heat shock response, as measured by HAMK activation and HSP70 accumulation, requires phospholipid signaling and mobilization of vacuolar Ca2+. Thus, the PIP2-PLC pathway appears to play a key role in thermotolerance after heat shock treatment.
Ahmed Mansour, Ahmed Shawky (Egypt), Rajinder Dhindsa (Canada) Membrane-based Activation of HSFs by Heat Shock in Tobacco Cells (pp 138-144)
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ABSTRACT
Original Research Paper: The range of temperature fluctuation which a plant can withstand depends on its genotype and on the available time to acclimatize to novel temperature. The plant responses are entirely mediated by signaling processes by which the plant can sense the changes in the environment and signal its genes to respond. A family of nuclear-encoded trans-acting transcription factors, termed the heat shock factors (HSFs), governs the expression of heat shock proteins (HSPs), which in turn, protect plant from heat shock effects. The enhanced expression of HSPs is regulated by heat shock factors (HSFs). Plant HSFs are structurally complex and they are typically composed of multiple exons and introns in the encoding region. In the present investigation, a 7-day old tobacco (Nicotiana tabacum cv. ‘Bright Yellow 2’) cell culture was used to investigate the membrane-based heat activation of HSFs under heat shock. A time course study of HSF1 and HSF2 accumulation using immunoblotting was used to study the synchronization of both HSFs activation in the cells. The effect of membrane fluidity and cytoskeleton reorganization in activating and accumulation of HSF1 and HSF in tobacco cells were demonstrated. In addition, the role of the Heat Activated MAP Kinase (HAMK) in mediating the activation of HSFs was also examined. Comparative analysis of tobacco HSFs and their counterparts in different organisms revealed a high degree of similarities in a corresponding domain, indicating similar function.
Ramzi Murshed, Félicie Lopez-Lauri, Cyril Keller, Fabien Monnet, Huguette Sallanon (France) Acclimation to Drought Stress Enhances Oxidative Stress Tolerance in Solanum lycopersicum L. Fruits (pp 145-151)
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ABSTRACT
Original Research Paper: A moderate water deficit stress (S1) applied 10 days after anthesis was found to induce acclimation to a subsequent more severe drought stress (S2) in Solanum lycopersicum L.. When plants were pretreated with S1, and then subjected to S2, fruit water status remained similar to controls. In contrast, S2 induced a decrease in both parameters of water status and diameter of fruits from non-acclimated (NA) plants. Following severe water stress, SOD, CAT and GR activities increased in NA fruits while APX and GR activities decreased in acclimated ones. On the other hand, membrane injury and H2O2 level increased in NA fruits submitted to S2. These results suggest that growing tomato fruits can acclimate to a moderate water deficit stress which moreover improves their ability to survive a more severe stress in the future with the development of less oxidative damage to fruits cells as indicated by MDA content.
Naotaka Furuichi, Kazutoshi Yokokawa, Tamiaki Ichihara (Japan) Ca2+-Dependent Protein Kinase in Tomato is Stimulated by Host-Selective Toxin from Alternaria solani (pp 152-155)
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Original Research Paper: We demonstrated that a fusion protein with a calcium-dependent protein kinase (CDPK) activity from the potato RiCDPK2 gene, purified from Escherichia coli, was stimulated by two toxins from tomato early blight (Alternaria solani). The kinase activity of the RiCDPK2 fusion protein was stimulated by a host-specific toxin (HST), alternaric acid, and a non host-specific toxin, solanapyrone A, both produced by A. solani. The addition of Ca2+ and Mg2+ was required for the stimulation of kinase activity. We suggest that the HST from A. solani may stimulate RiCDPK2 kinase activity during the infection process as part of the process that leads to the compatible interaction between tomato and A. solani, comparable to the role of suppressor from Phytophthora infestans which inhibits the occurrence of hypersensitive cell death during the potato-P. infestans interaction.
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