Antioxidant responses in roots of two contrasting <Emphasis Type="Italic">Sedum alfredii</Emphasis> Hance ecotypes under elevated zinc concentrations

Effects of different zinc concentrations on antioxidant responses in the roots of the hyperaccumulating ecotype (HE) and nonhyperaccumulating ecotype (NHE) of Sedum alfredii Hance were investigated under hydroponic conditions. Growth of NHE was inhibited significantly when Zn concentration was >-50 μM, whereas high Zn concentrations were beneficial for HE growth, and 500 μM Zn induced a significant increase in the root biomass and reducing activity. Malondialdehyde content and electrical conductivity of the NHE roots increased significantly; however, no changes were observed in HE when the Zn concentration was >10 μM, suggesting a severe damage to the membrane of the NHE roots. Proline content in NHE roots increased rapidly, whereas it was low in HE roots even at high Zn concentrations, suggesting that proline may not play an important role in Zn hyperaccumulation. The activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (GPX) in NHE roots increased significantly when the Zn concentration was >10 μM and decreased sharply when the Zn concentration was >-500 μM. For roots of HE, in contrast, no significant changes were observed in SOD, CAT, APX, and GPX activities at low Zn concentrations, whereas a high Zn concentration (≥500 μM) led to a marked enzyme activation, which was in accordance with Zn accumulation in shoots. The results suggest that antioxidant enzymes were important for Zn detoxification in NHE at low Zn concentrations (10–250 μM) and were more critical for Zn detoxification and hyperaccumulation in HE under elevated Zn concentrations (500–1000 μM).     

Zinc depletion efficiently inhibits pancreatic cancer cell growth by increasing the ratio of antiproliferative/proliferative genes

We investigated the ability of the zinc chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) to reduce pancreatic cancer cell viability. TPEN was much more efficient to inhibit pancreatic adenocarcinoma cell growth than a panel of anti-cancer drugs, including 5-fluorouracil, irinotecan, cisplatin, edelfosine, trichostatin A, mitomycin C, and gemcitabine, the gold standard chemotherapeutic agent for pancreatic cancer. Moreover, TPEN showed a dose- and time-dependent anti-proliferative effect significantly higher on pancreatic cancer cells than on normal primary fibroblasts. This effect may be explained by a significantly higher zinc depletion by TPEN in pancreatic cancer cells as compared to fibroblasts. Cell viability reduction by TPEN was associated to both G1-phase cell cycle arrest and apoptosis, and to the increased ratio of the expression level of cyclin-Cdk inhibitor versus cyclin genes and apoptotic versus anti-apoptotic genes. Finally, we show that apoptotic cell death induced by TPEN involved mitochondrial injury and caspase 3 and caspase 8 activation. In this study, we suggest that zinc depletion may be an efficient strategy in the treatment of pancreatic cancer because of its reduced antiproliferative effect on normal cells.     

Structural characterization of the zinc binding domain in cytosolic PSD-95 interactor (cypin): Role of zinc binding in guanine deamination and dendrite branching

Dendrite morphology regulates how a postsynaptic neuron receives information from presynaptic neurons. The specific patterning of dendrite branches is promoted by extrinsic and intrinsic factors that trigger the activation of functional signaling pathways. However, most of the regulating factors and the biochemical mechanisms involved in regulating dendrite branching are unknown. Our laboratory previously reported that cypin (cytosolic PSD-95 interactor) plays an active role in regulating dendrite branching in hippocampal neurons. Cypin-promoted increases in dendrite number are dependent on guanine deaminase activity. In order to identify the specific structural role of zinc-binding in cypin-mediated dendrite branching and guanine deaminase activity, we employed computational homology modeling techniques to construct a three dimensional structural model of cypin. Analysis of the protein-ion sequestration scaffold of this model identified several histidines and aspartic acid residues responsible for zinc binding. Single substitution mutations in these specific sites completely disrupted the guanine deaminase enzymatic activity and rendered cypin unable to promote dendrite branching in rat hippocampal neurons. The specific zinc ion-binding function of each residue in the protein scaffold was also confirmed by Inductively Coupled Plasma-Optic Emission Spectrometry. Inspection of our structural model confirmed that His82 and His84 coordinate with the zinc ion, together with His240, His279, and Asp330, residues that until now were unknown to play a role in this regard. Furthermore, promotion of dendrite branching by cypin is zinc-dependent.     

Synthesis and luminescent properties of a novel bluish‐white afterglow phosphor,b‐Zn3(PO4)2:Hf4+

A new bluish‐white long‐lasting phosphorescent material, Hf⁴⁺‐doped b‐Zn₃(PO₄)₂, was prepared by the conventional high‐temperature solid‐state method. The photoluminescence (PL) spectrum reveals that it exhibits a strong blue emission band centred at 470 nm, with asymmetry on the long wavelength side; this material emits bluish‐white light and shows strong afterglow phosphorescence after it is excited with a 254 nm UV lamp. The phosphorescence lasts nearly 40 min in the light perception of the dark‐adapted human eye (0.32 mcd/m²). The possible phosphorescence mechanism is also analysed. Copyright © 2008 John Wiley & Sons, Ltd.     

Interaction of heavy metals with the sulphur metabolism in angiosperms from an ecological point of view

The metabolism of sulphur in angiosperms is reviewed under the aspect of exposure to ecologically relevant concentrations of sulphur, heavy metals and metalloids. Because of the inconsistent use of the term 'metal tolerance', in this review the degree of tolerance to arsenic and heavy metals is divided into three categories: hypotolerance, basal tolerance and hypertolerance. The composition of nutrient solutions applied to physiological experiments let see that the well-known interactions of calcium, sulphate and zinc supply with uptake of heavy metals, especially cadmium are insufficiently considered. Expression of genes involved in reductive sulphate assimilation pathway and enzyme activities are stimulated by cadmium and partially by copper, but nearly not by other heavy metals. The synthesis of the sulphur-rich compounds glucosinolates, metallothioneins and phytochelatins is affected in a metal-specific way. Phytochelatin levels are low in all metal(loid)-hypertolerant plant species growing in the natural environment on metal(loid)-enriched soils. If laboratory experiments mimic the natural environments, especially high Zn/Cd ratios and good sulphur supply, and chemical analyses are extended to more mineral elements than the single metal(loid) under investigation, a better understanding of the impact of metal(loid)s on the sulphur metabolism can be achieved.     

Solanum tuberosum ZPR1 encodes a light‐regulated nuclear DNA‐binding protein adjusting the circadian expression of StBBX24 to light cycle

ZPR1 proteins belong to the C4‐type of zinc finger coordinators known in animal cells to interact with other proteins and participate in cell growth and proliferation. In contrast, the current knowledge regarding plant ZPR1 proteins is very scarce. Here, we identify a novel potato nuclear factor belonging to this family and named StZPR1. StZPR1 is specifically expressed in photosynthetic organs during the light period, and the ZPR1 protein is located in the nuclear chromatin fraction. From modelling and experimental analyses, we reveal the StZPR1 ability to bind the circadian DNA cis motif ‘CAACAGCATC’, named CIRC and present in the promoter of the clock‐controlled double B‐box StBBX24 gene, the expression of which peaks in the middle of the day. We found that transgenic lines silenced for StZPR1 expression still display a 24 h period for the oscillation of StBBX24 expression but delayed by 4 h towards the night. Importantly, other BBX genes exhibit altered circadian regulation in these lines. Our data demonstrate that StZPR1 allows fitting of the StBBX24 circadian rhythm to the light period and provide evidence that ZPR1 is a novel clock‐associated protein in plants necessary for the accurate rhythmic expression of specific circadian‐regulated genes.