Dejana Panković

Zinc-induced oxidative stress in Verbascum thapsus is caused by an accumulation of reactive oxygen species and quinhydrone in the cell wall

Oxidative stress is one aspect of metal toxicity. Zinc, although unable to perform univalent oxido-reduction reactions, can induce the oxidative damage of cellular components and alter antioxidative systems. Verbascum thapsus L. plants that were grown hydroponically were exposed to 1 and 5 mM Zn²+. Reactive oxygen species (ROS) accumulation was demonstrated by the fluorescent probe H₂ DCFDA and EPR measurements. The extent of zinc-induced oxidative damage was assessed by measuring the level of protein carbonylation. Activities and isoform profiles of some antioxidant enzymes and the changes in ascorbate and total phenolic contents of leaves and roots were determined. Stunted growth because of zinc accumulation, preferentially in the roots, was accompanied by H₂O₂ production in the leaf and root apoplasts. Increased EPR signals of the endogenous oxidant quinhydrone, •CH₃ and •OH, were found in the cell walls of zinc-treated plants. The activities of the antioxidative enzymes ascorbate peroxidase (APX) (EC 1.11.1.11), soluble superoxide dismutase (SOD) (EC 1.15.1.1), peroxidase (POD), (EC 1.11.1.7) and monodehydroascorbate reductase (EC 1.6.5.4) were increased; those of glutathione reductase (EC 1.6.4.2), dehydroascorbate reductase (EC 1.8.5.1) and ascorbate oxidase (AAO) (EC 1.10.3.3) were decreased with zinc treatment. Zinc induced a cell-wall-bound SOD isoform in both organs. Leaves accumulated more ascorbate and phenolics in comparison to roots. We propose a mechanism for zinc-promoted oxidative stress in V. thapsus L. through the generation of charge transfer complexes and quinhydrone because of phenoxyl radical stabilisation by Zn²+ in the cell wall. Our results suggest that the SOD and APX responses are mediated by ROS accumulation in the apoplast. The importance of the POD/Phe/AA (ascorbic acid) scavenging system in the apoplast is also discussed.

Effect of the edaphic factors and metal content in soil on the diversity of Trichoderma spp.

Influence of edaphic factors and metal content on diversity of Trichoderma species at 14 different soil sampling locations, on two depths, was examined. Forty-one Trichoderma isolates from 14 sampling sites were determined as nine species based on their internal transcribed spacer (ITS) sequences. Our results indicate that weakly alkaline soils are rich sources of Trichoderma strains. Also, higher contents of available K and P are connected with higher Trichoderma diversity. Increased metal content in soil was not inhibiting factor for Trichoderma species occurrence. Relationship between these factors was confirmed by locally weighted sequential smoothing (LOESS) nonparametric smoothing analysis. Trichoderma strain (Szeged Microbiology Collection (SZMC) 22669) from soil with concentrations of Cr and Ni above remediation values should be tested for its potential for bioremediation of these metals in polluted soils.

The influence of Trichoderma brevicompactum treatment and drought on physiological parameters, abscisic acid content and signalling pathway marker gene expression in leaves and roots of tomato

Faculty of Ecological Agriculture, Educons University, Sremska Kamenica, Serbia Faculty of Agriculture, University of Belgrade, Zemun, Serbia Research Center for Technology of Plant Based Food Products, Institute of Food Technology, Novi Sad, Serbia Maize department, Institute of Field and Vegetable Crops, Novi Sad, Serbia Correspondence Prof. Dejana Pankovi c, Faculty of Ecological Agriculture, Educons University, Vojvode Putnika 87, Sremska Kamenica, Serbia. Email: dejana.pankovic@educons.edu.rs Funding information English-Ministry of Education, Science and Technological development of the Republic of Serbia, Grant/Award Number: III43010; TR 31005; TR 31080 Trichoderma species are widely known for their antagonistic properties, but plant growth promotion and abiotic stress tolerance have also been reported. Mechanisms of abiotic stress tolerance, such as drought in plants in interaction with Trichoderma spp., remain unclear. In this work, the results about the influence of Trichoderma brevicompactum on the physiological parameters and abscisic acid (ABA) content in leaves and roots of tomato, as well as the Trichodermamodulated plant response to drought are presented. Both in optimally watered plants and droughted plants treated with Trichoderma, the relative water content (RWC) was 17% higher than in untreated plants. Drought lowered RWC by 25% in both Trichoderma-untreated and -treated plants. Under drought conditions, the better water status of plants treated with Trichoderma is connected with lower stomatal conductance and closure of stomata. The lower increase of root ABA content in Trichoderma-treated plants that we observed could be an adaptive advantage in sense of smaller inhibition of plant growth induced by drought. Trichoderma modulation of the salicylic acid (SA) marker genes response to drought was observed in leaves. Our results suggest that signalling pathways of jasmonic acid (JA), SA and ABA are involved in response to both drought and Trichoderma. The mutual effect of the tested treatments leads to the modification of gene expression in comparison to the reaction to a single stress. The upregulation of SA marker genes in leaves and JA marker genes in the roots 2 weeks after the interaction with T. brevicompactum indicates that it could be promising biocontrol agent.

Early Response of Defense Related Genes to Secondary Downy Mildew Infection in Sunflower Line with Pl6 Gene

Abstract Sunflower line with resistance for downy mildew (Ha-26R) and susceptible line (Ha-26S) were inoculated with the suspension of Plasmopara halstedii zoosporangia, race 730, in the phase of first pair of leaves. The expression of defense related genes was investigated in the time period of 2 to 96 h after treatment. Several categories of defense-related genes: signalization (EDS1 and EDR1); H2O2 producing (Hacaox and Haoxox); antioxidative response (SODc and SODp), pathogenesis related (chi, PAL, PR5) were examined. Most examined defense related genes were constitutive with higher expression in resistant line. However, in response to secondary downy mildew infection six genes were upregulated. Upregulation of HaEDS1 signaling gene 2 h after infection indicates that SA mediated response is activated. Pathogenesis related genes: chitinase and PR5, were also upregulated in the earliest time point. Other defense related genes: SODp, Caox and OxOx were sequentially upregulated from 4 to 48 h after infection in resistant line. Our results indicate that the early response of defense related genes to secondary downy mildew infection, resembles to hypersensitive-like reaction and is connected with resistance conferred by Pl6 gene. According to our results resistance to secondary infection is characterized with earlier upregulation of PR5 in comparison to primary infection.