Tamas Komives

Local and Systemic Responses of Antioxidants to Tobacco Mosaic Virus Infection and to Salicylic Acid in Tobacco (Role in Systemic Acquired Resistance).

Changes in ascorbate and glutathione levels and in activities of ascorbate peroxidase, catalase, dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione S-transferase (GST), and superoxide dismutase (SOD) were investigated in tobacco mosaic virus (TMV)-inoculated lower leaves and in non-inoculated upper leaves of Nicotiana tabacum L. cv Xanthi-nc. In separate experiments the effects of exogenous salicylic acid (SA) were also studied. Symptom appearance after TMV inoculation was preceded by a slight, transient decline of ascorbate peroxidase, GR, GST, and SOD activities in the inoculated lower leaves, but after the onset of necrosis these activities and the glutathione level substantially increased. Ascorbic acid level and DHAR activity declined and dehydroascorbate accumulated in the inoculated leaves. In upper leaves, the glutathione level and the activities of GR, GST, and SOD increased 10 to 14 d after TMV inoculation of the lower leaves, concomitantly with the development of systemic acquired resistance. From the six distinct SOD isoenzymes found in tobacco leaves, only the activities of Cu,Zn-SOD isoenzymes were affected by TMV. SA injection induced DHAR, GR, GST, and SOD activities. Catalase activities were not modified by TMV infection or SA treatment. It is supposed that stimulated antioxidative processes contribute to the suppression of necrotic symptom development in leaves with systemic acquired resistance.

Overcoming ammonium toxicity

Ammonia (ammonium ion under physiological conditions) is one of the key nitrogen sources in cellular amino acid biosynthesis. It is continuously produced in living organisms by a number of biochemical processes, but its accumulation in cells leads to tissue damage. Current knowledge suggests that a few enzymes and transporters are responsible for maintaining the delicate balance of ammonium fluxes in plant tissues. In this study we analyze the data in the scientific literature and the publicly available information on the dozens of biochemical reactions in which endogenous ammonium is produced or consumed, the enzymes that catalyze them, and the enzyme and transporter mutants listed in plant metabolic and genetic databases (Plant Metabolic Network, TAIR, and Genevestigator). Our compiled data show a surprisingly high number of little-studied reactions that might influence cellular ammonium concentrations. The role of ammonium in apoptosis, its relation to oxidative stress, and alterations in ammonium metabolism induced by environmental stress need to be explored in order to develop methods to manage ammonium toxicity.

Elevation of glutathione level and activation of glutathione-related enzymes affect virus infection in tobacco.

The effects of two chemicals, L-2-oxothiazolidine-4-carboxylic acid (OTC) and (S)-carvone, were investigated on the development of necrotic symptoms and on the virus concentration in tobacco mosaic virus (TMV)-infected tobacco plants. OTC treatments markedly increased the cellular glutathione (GSH) levels in tobacco leaf discs. In addition, OTC pretreatment considerably decreased both the number of necrotic lesions and the virus content in TMV-infected leaf discs. The monoterpene (S)-carvone increased only slightly the GSH content of leaf tissues and caused lipid peroxidation. (S)-carvone dramatically induced the activity of glutathione S-transferase and to a lesser extent elevated also the activities of ascorbate peroxidase and glutathione reductase. Treatments with (S)-carvone strongly reduced the number and size of necrotic lesions, but did not influence the virus concentration. The results show that increased levels of GSH and activities of GSH-related enzymes by OTC and (S)-carvone reduce necrotization of virus-infected tissues. However, virus multiplication and lesion formation do not necessarily correlate: virus multiplication is suppressed only by substantially elevated GSH contents.

AFLP analysis and improved phytoextraction capacity of transgenic gshI-poplar clones (Populus x canescens L.) for copper in vitro

Abstract Clone stability and in vitro phytoextraction capacity of vegetative clones of P. x canescens (2n = 4x = 38) including two transgenic clones (ggs11 and lgl6) were studied as in vitro leaf disc cultures. Presence of the gshI-transgene in the transformed clones was detected in PCR reactions using gshI-specific primers. Clone stability was determined by fAFLP (fluorescent amplified DNA fragment length polymorphism) analysis. In total, 682 AFLP fragments were identified generated by twelve selective primer pairs after EcoRIDMseI digestion. Four fragments generated by EcoAGTDMseCCC were different (99.4% genetic similarity) which proves an unexpectedly low bud mutation frequency in P. \ canescens. For the study of phytoextraction capacity leaf discs (8 mm) were exposed to a concentration series of ZnSO4 (10-1 to 10-5 ᴍ) incubated for 21 days on aseptic tissue culture media WPM containing 1 μᴍ Cu. Zn2+ caused phytotoxicity only at high concentrations (10-1 to 10-2 ᴍ). The transgenic poplar cyt-ECS (ggs11) clone, as stimulated by the presence of Zn, showed elevated heavy metal (Cu) uptake as compared to the non-transformed clone. These results suggest that gshI-transgenic poplars may be suitable for phytoremediation of soils contaminated with zinc and copper.

Ability of Poplar (Populus spp.) to Detoxify Chloroacetanilide Herbicides

The ability of poplar trees to resist chemical stress caused by chloroacetanilide herbicides was studied. Detached leaves of Lombardy poplar (Populus nigra L.) were exposed to seven chloroacetanilide herbicides via uptake through the cut petiole. The leaves showed high tolerance against the phytotoxicity of these compounds. Their tolerance was further enhanced by treatment with 2-oxothiazolidine-4-carboxylic acid (OTC, a precursor of the amino acid cysteine). High levels of glutathione (GSH) and GSH S-transferase (GST) activity were detected in poplar leaves. Treatments with chloroacetanilide herbicides left the GSH content in the leaves unchanged but strongly induced the GST activity. In contrast, in OTC-treated leaves increased GSH contents were measured, but GST activities remained unchanged. It therefore appears that a highly active and inducible GSH-conjugation Phase II detoxification system in their leaves may make poplar trees useful for phytoremediation of soils contaminated with chloroacetanilide herbicides. Based on these findings a phytoremediation project using different poplar hybrids at a site heavily polluted with such compounds in Hungary has been launched.

Loss of Nutrients Caused by Excessive Weediness at the Early Stage of Maize Vegetation Period

Abstract The experiment was carried out in a field previously not exposed to herbicides, in which jimsonweed (Datura stramonium L.) and wild hemp (Cannabis sativa spp. spontanea) were the dominant weeds. Using sites identified with global positioning system (GPS) coordinates, changes in abundance of weeds in time were investigated. Before the trial in autumn, soil samples were taken for analysis. Nutrient uptake was determined and compared with the results of the spring plant examinations. One month after the sowing of maize (Zea mays L.), the total number of weeds and the number of weed species present at the sampling sites were determined, and aerial fresh and dry weights of the crop and weed plants were measured. Plant tissue samples were assayed for contents of nitrogen, phosphorus, potassium, and calcium, and data obtained from weedy and weed‐free control areas were compared. Similarly, maize yields were determined, and their dependence on plot weediness was evaluated. We found that uptake of large amounts of nutrients by jimsonweed and wild hemp at the early stage of the development of maize is an important factor in crop‐weed competition.

RT-PCR analysis and stress response capacity of transgenic gshi-poplar clones (Populus x canescens) in response to paraquat exposure

Abstract Stress response capacity (Fv/Fm at 690 nm and F690/F735 at Fmax) of untransformed hybrid poplar, Populus × canescens (P. tremula × P. alba), and two transgenic lines overexpressing γ-ECS (γ-glutamylcysteine synthetase) either in the cytosol (cyt-ECS) or in the chloroplast (chl-ECS) was studied in response to the herbicide paraquat (4.0 × 10-9 to 4.0 × 10-6 m) for 21 days. Significant differences at sublethal (4.0 × 10-7 m) and bleaching (4.0 × 10-6 m) concentrations of paraquat were observed with about a two-fold and eight-fold decrease in the photosynthetic activity (Fv/Fm at 690 nm and F690/F735 at Fmax), respectively. None of the gshI transgenic lines (cyt-ECS, chl-ECS) with elevated GSH content exhibited significant tolerance to paraquat. Semiquantitative RT-PCR of the cyt-ECS clone was used for gene expression analysis of the nuclear encoded rbcS gene and the stress responsive gst gene. Expression of the constitutively expressed 26SrRNA ribosomal gene was probed as a control for all RT-PCR reactions. The relative intensities of gene expressions normalized to the level of 26SrRNA intensity showed a 50% decrease in the nuclear encoded rbcS expression and a 120% increase in the stress responsive gst gene expression of the paraquat treated (4.0 × 10-7 m) samples of the transgenic poplar line (cyt-ECS).

Effect of weediness on the water content of the soil: A field study

Abstract Maize is a vigorous and tall‐growing plant. Still, as a widely spaced crop, maize is highly susceptible to competition from weeds during its early growth period, with losses greater than 30% commonly reported. To characterize the nature of maize–weed competition, nutrient and water contents of maize and weed plants and the soil were determined in a field study. The experiment was carried out at Baracska, Hungary, in 2003, in a 9.2‐ha project area. Sampling areas (2×2 m in size, 21 altogether) were assigned, identified with global positioning system (GPS) coordinates, and left without weed control. After the emergence of maize, the frequency and density of weeds at the sampling sites were regularly determined, and samples of crop and weed plants and soil (from the depths of 0–20, 20–40, 40–60, 60–80, and 80–100 cm) were taken for analysis of water and nutrient contents. Three weed species were dominant: jimsonweed (Datura stramonium L.), broomcorn millet (Panicum miliaceum L.), and wild hemp (Cannabis sativa L.). A linear negative relationship was observed between the weediness and the water content in the top 20‐cm layer of the soil at the sampling areas.

ON THE MODE OF ACTION OF EPTC AND ITS ANTIDOTES

Direct injection techniques have shown that the phytotoxicity to corn of EPTC-sulfone, EPTC and EPTC-sulfoxide is decreasing in this order, and the mixed function oxidase inhibitors piperonyl butoxide and SKF-525A are synergists but glutathione is an antagonist for the toxic action of EPTC. From these results it is concluded that 1/ sulfoxidation and glutathione conjugation are equally important for the detoxification of EPTC, 2/ these processes play a key role in the antidote effect, 3/ phytotoxicity of EPTC to corn is not due to the action of sulfone and is only partly due to the sulfoxide metabolite. A phytotoxic mechanism of EPTC not involving the sulfoxide is suggested. An attempt to find relationship between acylation reactivity and antidote activity of amides, esters and thiolesters is described.

Diphenyl Ether Herbicides: Effects of Acifluorfen on Phenylpropanoid Biosynthesis and Phenylalanine Ammonia-Lyase Activity in Spinach'

Abstract Spinach leaves treated with acifluorfen synthesize >25-fold the normal level of the phenolic amide (I) derived from ferulic acid and 3-methoxytyramine. The content of I is increased within 18 hr and at acifluorfen concentrations as low as 0.2 ppm. Biosynthesis experiments with precursor 14C-amino acids establish that the elevated content of I is due to de novo synthesis with the acyl moiety derived from phenylalanine, the amine moiety from tyrosine, and the O-methyl groups from methionine. Elevation of I content is followed by the appearance of necrotic lesions in spinach leaves but is preceded by an increase in extractable phenylalanine ammonia-lyase activity, detectable 9 hr after treatment, reaching 13-fold of normal values at 20 hr, and dropping to near control activity at 48 hr. Phenylalanine ammonia-lyase activity is also elevated by acifluorfen in soybeans and six other crops or weeds. Alterations in aromatic amino acid metabolism and phenylpropanoid biosynthesis involving secondary phenolic compounds may contribute to the phytotoxic effects of diphenyl ether herbicides.