Joanna Deckert

The new insights into cadmium sensing

Cadmium (Cd) is non-essential heavy metal, which in excess, exhibits deleterious effects to the most of the organisms. Mobilization of defense mechanisms against this toxic agent requires rapid activation of signaling pathways. The article presents recent advances in the research concerning cadmium signal transduction in plants. New insights into the involvement of reactive oxygen species (ROS), nitric oxide (NO), plant growth regulators, and Cd-induced protein modifications are reviewed. Moreover, the role of recently recognized Cd-associated signal elements, including micro RNAs and several cis- and trans-acting elements is discussed.

Plant cell responses to heavy metals: molecular and physiological aspects

The effect of lead, cadmium and cooper on protein pattern, free radicals and antioxidant enzymes in root of Lupinus luteus L. were investigated. Heavy metals inhibited growth of lupin roots, which was accompanied by increased synthesis and accumulation of a 16 kDa polypeptide (Przymusiński et al. 1991 Biochem. Physiol. Pflanzen., 187:51–57). This component has been earlier identified as immunologically related to Cu,Zn-superoxide dismutase (Przymusiński et al. 1995 Env.Exp.Bot., 35:485–495). However, more detailed study revealed that this stress-stimulated protein is composed of four to six polypeptides of different electrophoretic mobility. The most abundant polypeptides of the 16kDa region were found to be closely homologous to pathogen related proteins. The number and intensity of these polypeptides was highly variable in roots of individual seedlings, which suggests that they might represent separate allelic forms.Electron paramagnetic spectra revealed that at low lead concentrations the amplitude of the first derivative was similar to the control and distinctly increased at higher metal concentrations. On the other hand, at the lower lead concentrations the activity of antioxidant enzymes increased, whereas at higher metal doses the enzyme activities did not raise further (SOD) or even dropped (CAT, APOX). This implies that the responses of antioxidant system to lead is dose-dependent stimulated by low metal concentrations, whereas at the higher metal level the free radical emission is beyond the quenching capacity of antioxidant enzymes, which in turn might contribute to the reduced root growth.The effect of various heavy metals: Pb2+, Cd2+ and Cu2+ on phytochelatins and antioxidant enzymes depends on the kind of metal ion. Pb2+ and Cd2+ stimulated the PCs formation whereas Cu2+ was not effective. On the other hand, in root exposed to Cu the activity of catalase (CAT) was the highest as was the production of H2O2. The strong oxidative effect of Cu2+ ions which were not complexed by PCs suggests that these peptides might by involved in the cellular defense system by binding excessive heavy metal ions.On the basis of our results it can be concluded that in lupin roots exposed to heavy metals there is a complex defense system against metal phytotoxicity, which comprises of specific proteins, antioxidant enzymes and phytochelatins.

Nitric oxide implication in cadmium-induced programmed cell death in roots and signaling response of yellow lupine plants.

The sequence of events leading to the programmed cell death (PCD) induced by heavy metals in plants is still the object of extensive investigation. In this study we showed that roots of 3-day old yellow lupine (Lupinus luteus L.) seedlings exposed to cadmium (Cd, 89μM CdCl(2)) resulted in PCD starting from 24h of stress duration, which was evidenced by TUNEL-positive reaction. Cd-induced PCD was preceded by a relatively early burst of nitric oxide (NO) localized mainly in the root tips. Above changes were accompanied by the NADPH-oxidase-dependent superoxide anion (O(2)(·-)) production. However, the concomitant high level of both NO and O(2)(·-) at the 24th h of Cd exposure did not provoke an enhanced peroxynitrite formation. The treatment with the NADPH-oxidase inhibitor and NO-scavenger significantly reduced O(2)(·-) and NO production, respectively, as well as diminished the pool of cells undergoing PCD. The obtained data indicate that boosted NO and O(2)(·-) production is required for Cd-induced PCD in lupine roots. Moreover, we found that in roots of 14-day old lupine plants the NO-dependent Cd-induced PCD was correlated with the enhanced level of the post-stress signals in leaves, including distal NO cross-talk with hydrogen peroxide.

Cadmium-induced changes in growth and cell cycle gene expression in suspension-culture cells of soybean

Abstract The toxic effects of cadmium on growth and development of living organisms are well documented. However, the molecular mechanisms responsible for the inhibition of plant growth by cadmium are still not completely understood. We determined the effects of cadmium concentrations in the range of 1–11 μM on the growth of Glycine max L. cv. Navico suspension-culture cells, as well as on the expression of two cell cycle genes: cyclin B1 and cyclin-dependent type A kinase (CDK-A). There was no detectable decrease in cell viability at any tested Cd 2+ concentrations. The lower concentrations of Cd 2+ (1–4 μM) stimulated cell culture growth; however, this did not correspond with increased expression of cell cycle genes. The inhibition of cell growth was observed at concentration of Cd 2+ higher than 6 μM. Interestingly, it correlated well with the decreased cyclin B1 mRNA levels, but had no significant effect on the levels of CDK-A mRNA.

The effect of cadmium on cell cycle control in suspension culture cells of soybean

Heavy metals inhibit plant growth. This proces may be directly or indirectly connected with mechanisms regulating cell division. We analyzed the effect of Cd2+ on cell cycle progression in partially synchronized soybean (Glycine max) cell suspension culture and followed the expression of cell cycle genes (cyclin B1 and cyclin-dependent kinase A - CDK-A). We have checked the hypothesis that Cd2+-induced impairment of cell division is connected with DNA damage. The [3H]-thymidine incorporation in cell cultures synchronized either with hydroxyurea (HU) or phosphate starvation have shown, that Cd2+ strongly affects the S phase of soybean cell cycle, by causing the earlier entry of cells into S phase and by decreasing the rate of DNA synthesis. RT-PCR analysis indicated that Cd2+ decreases the level of cyclin B1 mRNA and has no effect on CDK-A mRNA. The result of comet assay indicated the damaging effect of Cd2+ on DNA of soybean cells. We suggest that Cd2+ affects plant cell cycle at two major checkpoints: the G1/S — by damaging of DNA, and G2/M - by decreasing the level of cyclin B1 mRNA

Nitric Oxide-Mediated Stress Imprint in Potato as an Effect of Exposure to a Priming Agent

We investigated how potato exposed to a chemical agent could activate nitric oxide (NO)-dependent events facilitating more potent defense responses to a subsequent pathogen attack. Obtained data revealed that all applied inducers, i.e., β-aminobutyric acid (BABA), γ-aminobutyric acid (GABA), laminarin, or 2,6-dichloroisonicotinic acid (INA), were active stimuli in potentiating NO synthesis in the primed potato. It is assumed, for the mechanism proposed in this paper, that priming involves reversible S-nitrosylated protein (S-nitrosothiols [SNO]) storage as one of the short-term stress imprint components, apart from epigenetic changes sensitized by NO. Based on BABA- and GABA-induced events, it should be stated that a rise in NO generation and coding the NO message in SNO storage at a relatively low threshold together with histone H2B upregulation might create short-term imprint activation, facilitating acquisition of a competence to react faster after challenge inoculation. Laminarin elicited strong NO upregulation with an enhanced SNO pool-altered biochemical imprint in the form of less effective local recall, nevertheless being fully protective in distal responses against P. infestans. In turn, INA showed the most intensified NO generation and abundant formation of SNO, both after the inducer treatment and challenge inoculation abolishing potato resistance against the pathogen. Our results indicate, for the first time, that a precise control of synthesized NO in cooperation with reversible SNO storage and epigenetic modifications might play an important role in integrating and coordinating defense potato responses in the priming phenomenon.

Phenylpropanoid pathway metabolites promote tolerance response of lupine roots to lead stress

Over the past decade, there has been increasing interest in the role of phenolic compounds, especially flavonoids in plants in response to heavy metal stress. In this study, it was found that treatment of yellow lupine (Lupinus luteus L.) with Pb (150mg/l Pb(NO3)2) increased flavonoid contents in both cotyledons (by ca. 67%) and roots (by ca. 54%). Moreover, seedling roots preincubated with flavonoid extracts, derived from Pb-treated lupine cotyledons, exhibited enhanced tolerance to the heavy metal. Flavonoid preincubated lupine seedlings, growing for 48h in the presence of Pb(NO3)2, showed mitigated symptoms of lead stress, which was manifested by a significant increase in the root length and its biomass. Additionally, in seedlings pretreated with the natural flavonoid preparations an impressive rise of the antioxidant capacity was observed. Simultaneously, root cells exhibited reduced accumulation of both H2O2 and O2(-), which was associated with the decreased TBARS content and the number of dying cells under Pb stress. Taken together, accumulation of flavonoids could be an effective event in the plant׳s spectrum of defense responses to heavy metal stress, and the protective role of flavonoids against heavy metals might be associated with their ability to scavenge reactive oxygen species overproduced under lead stress.

Products of lipid, protein and RNA oxidation as signals and regulators of gene expression in plants

Reactive oxygen species (ROS) are engaged in several processes essential for normal cell functioning, such as differentiation, anti-microbial defense, stimulus sensing and signaling. Interestingly, recent studies imply that cellular signal transduction and gene regulation are mediated not only directly by ROS but also by the molecules derived from ROS-mediated oxidation. Lipid peroxidation leads to non-enzymatic formation of oxylipins. These molecules were shown to modulate expression of signaling associated genes including genes encoding phosphatases, kinases and transcription factors. Oxidized peptides derived from protein oxidation might be engaged in organelle-specific ROS signaling. In turn, oxidation of particular mRNAs leads to decrease in the level of encoded proteins and thus, contributes to the post-transcriptional regulation of gene expression. Present mini review summarizes latest findings concerning involvement of products of lipid, protein and RNA oxidation in signal transduction and gene regulation.

The modifying effect of sucrose on glutamate dehydrogenase (GDH) activity in lupine embryos treated with inhibitors of RNA and protein synthesis

The modifying effect of sucrose on GDH activity and isoenzyme pattern in isolated embryos of lupine subjected to treatments with inhibitors of RNA synthesis (transcription inhibitors: actinomycin D and cordycepin) and protein synthesis (cycloheximide and chloramphenicol) was investigated. Sucrose starvation of embryos caused the increase of total activity of GDH(NADH-GDH and NAD-GDH) more than twice. Supply of sucrose to sucrose starved embryos caused a reduction of enzyme activity by 40 %. Electrophoretic analysis showed the presence of ca 17 isoenzymes of glutamate dehydrogenase in embryos grown for 72 h in medium with sucrose, while sucrose starvation increased the number of isoenzymes up to 22 forms. Addition of sucrose to sucrose starved embryos after 24 h of cultivation caused the inhibition of synthesis of new isoenzymes. This down-regulation by sucrose was blocked when sucrose was added together with cycloheximide, CHX, (0.025 mM). Treatment of sucrose fed and sucrose starved embryos with cycloheximide (0.020 mM) inhibited protein synthesis by 58 % and 24 %, respectively. The addition of cycloheximide (0.025 mM) to sucrose starved embryos decreased by 60 % NADH-GDH and by 30 % NAD-GDH activity and reduced the spectrum of isoenzymes. CHX treatment did not lead to a significant reduction of enzyme activity and isoenzyme pattern in sucrose fed embryos. The chloramphenicol (CMP) treatment (1 mM) stimulated the total GDH activity, 2.5 fold and 1.5 fold, in sucrose fed and sucrose starved embryos, respectively. Addition of CMP (10 mM) to the media did not affect GDH activity. Both concentrations of CMP caused no significant changes in the isoenzymatic pattern of enzyme in sucrose starved embryos, but induction of new isoenzymes was observed in sucrose fed embryos treated with CMP. In the case of using RNA synthesis inhibitors only cordycepin inhibited the total GDH activity (by ca 25 %) but neither actinomycin D or cordycepin caused any changes in isoenzyme pattern of GDH. The possible mechanism of sugar-mediated regulation of GDH activity is discussed.

A common response to common danger? Comparison of animal and plant signaling pathways involved in cadmium sensing

Exposure to cadmium results in disturbances in cell homeostasis in all living organisms. The first response to stress factors, including cadmium, is activation of signal transduction pathways that mobilize cell defense mechanisms. The aim of this review is a comparison between the signaling network triggered by Cd in plants and animals. Despite differences in the structure and physiology of plant and animal cells, their cadmium signal transduction pathways share many common elements. These elements include signaling molecules such as ROS, Ca2+ and NO, the involvement of phospholipase C, mitogen-activated protein kinase cascades, and activation of transcription factors. Undoubtedly, both animals and plants also possess specific signaling pathways. In case of animals, Wnt/β-catenin, sonic hedgehog and oestorgen signaling are engaged in the transduction of cadmium signal. Plant specific signal transduction pathways include signaling mediated by plant hormones. The role of ethylene and jasmonic, salicylic and abscisic acid in plant response to cadmium is also discussed.