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Authors: E. Páldi and E. Páldi
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The mechanism of acetolactate synthase (ALS) resistance to the inhibitory action of sulfonylurea is due to the selection of R1 and R2 biotypes of C. arvense with modified form of the ALS enzyme. They are less susceptible to the inhibition of sulfonylurea, but still functional. There was no significant difference between the susceptible and sulfonylurea-resistant biotypes in absorption and translocation of chlorsulfuron.

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In the course of the Maize Consortium Project, investigations were made on the defence mechanisms employed by maize against various abiotic stress factors (low temperature, cadmium) and on the effects exerted by two compounds (S-methylmethionine, salicylic acid) capable of improving the stress resistance of plants to certain abiotic stresses. Salicylic acid (SA) was found to inhibit the uptake of cadmium (Cd), but caused damage to the roots, including a reduction in the activity of phytochelatin synthase (PCS), which meant that preliminary treatment with SA aggravated the damaging effect of Cd. It was also proved that as the result of 2-day treatment with Cd, there was a continuous rise in the Cd level in the plants, more Cd being accumulated in young leaves than in older ones. The PCS activity increased greatly after 24 hours, both in the leaves and in the roots, declining again after 2 days. The effect of SA was examined in both the hybrids and their parental lines, and the effect of this compound on the intensity of alternative respiration was also investigated. A comparison of chilling tolerance data and antioxidant enzyme activity indicated that these two parameters were not directly correlated to each other, i.e. antioxidant enzyme activity values could not be used to draw reliable conclusions on the chilling tolerance of maize lines and hybrids. With regard to the interaction between alternative respiration and salicylic acid, it was proved that exogenous hydrogen peroxide caused a similar increase in the ratio of alternative respiration to that observed after salicylic acid treatment. Abbreviations: SA, salicylic acid; Cd, cadmium; PCS, phytochelatin synthase; SMM, S-methylmethionine; PCs, phytochelatins; PAR, photosynthetically active radiation; TTC, triphenyl tetrazolium chloride; KCN, potassium cyanide; PSII, 2nd photochemical system; POD, guaiacol peroxidase; APX, ascorbate peroxidase; GR, glutathione reductase

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The plant hormones auxin, cytokinin and gibberellic acid, which stimulate plant growth and development, induce significant changes in the isoacceptor spectra of various tRNAs. The present experiments revealed that the treatment of wheat seedlings with auxin, cytokinin or gibberellic acid resulted in the appearance of new isoacceptors in the spectra of three tRNA groups specific for amino acids (methionine, tyrosine and valine). These new isoacceptors may be beneficial for the synthesis and regulation of the proteins induced by the plant hormones.

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The drought stress tolerance of three accessions of Aegilops biuncialis Vis. (Ae225, Ae550 and Ae1050) and two varieties of Triticum aestivum L. (Sakha and Cappelle Desprez) was compared. The activity of superoxide dismutase (SOD) isoenzymes, which reflects the intensity of oxidative stress, changes in the malonic dialdehyde (MDA) content, formed during the lipid peroxidation induced by stress situations, and the inducibility of electron removal systems appearing as an alternative to CO 2 fixation were chosen for the present investigations. Drought stress was simulated using polyethylene glycol (PEG). The order of drought stress tolerance obtained correlated well with the original habitats ofthe varieties. The present results provide a clear illustration of the fact that tolerant varieties respond differently for the parameters tested, suggesting that their resistance can be attributed to different mechanisms. Abbreviations:CuZnSOD=superoxide dismutase isoform with Cu and Zn cofactor metals, MnSOD and FeSOD=superoxide dismutase isoform with Mn and Fe cofactor metals, PVP25= polyvinyl pyrrolidone 25, MDA=malonic dialdehyde, PEG=polyethylene glycol, TCA=trichloro acetic acid, TBA=thiobarbituric acid, ΔF=F m -F s , F m =maximal fluorescence yield, F s =fluorescence yield in steady state

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The sectorial material transport disorders induced by cutting back were first detected some two decades ago (Brunner, 1976; 1990; Brunner et al., 1996). The pruning of oblique scaffold branches to an upper bud causes one-sided drying up and material transport disorders on the lower side of the branch, leading to the formation of close to horizontal shoots on the lower side of the scaffold branch without any tendency for the branch to become bare, and with a considerable reduction in manual labour requirements. This is the essence of this novel pruning method having a bending effect.

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Authors: T. Brunner, E. Páldi, L. Juhász, F. Tóth and J. Iváncsics

The physiologically-based pruning methods elaborated by the authors were found to increase intensity in various ways, including early fruiting, improved yield and quality, and a reduction in the height of the cropping area, allowing at least 80% of the fruit to be picked from the ground. Compared with the Lespinasse control, crowns with a valve-like central leader on a sectorial spindle gave a surplus yield of 8.5 t/ha/year over the average of 3 years, including an increase of 2.3 t/ha/year in the yield of extra quality and grade I fruit.

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The effect of 10, 25 and 50 μM Cd(NO 3 ) 2 on the fatty acid composition was investigated in young maize seedlings ( Zea mays L., hybrid Norma). After 7 days’ exposure to cadmium slight changes were observed in the fatty acid composition, which were more pronounced in the roots than in the leaves. In the leaves cadmium did not affect the lipid composition of the monogalactosyldiacylglycerol (MGDG) or digalactosyldiacylglycerol (DGDG) fractions, while in the phosphatidylethanolamine (PE) and phosphatidylglycerol (PG) fractions there was a decrease in the proportion of hexadecanoic acid (16:0) and an increase in the level of linoleic acid (18:2) and linolenic acid (18:3). The proportion of trans -Δ3-hexadecanoic acid in leaf PG also decreased. In the roots significant changes were observed in all the fractions examined after Cd stress. In the MGDG the level of stearic acid (18:0) and oleic acid (18:1) decreased, but that of 18:2 and 18:3 increased. In the case of PE the amount of 16:0 decreased, while that of 18:0, 18:1 and 18:3 increased. In the PG fraction the proportion of 16:0, 18:0 and 18:1 decreased, while that of 18:2 increased. The ratio of 16:0 also decreased in the DGDG fraction, while that of 18:0, 18:1 and 18:2 increased. The changes in the fatty acid composition were associated with an increase in the double-bond index and in the percentage of unsaturation in leaf PG, and in the MGDG, PG and DGDG fractions in the roots.

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Authors: M. Pogány, B. D. Harrach, Y. M. Hafez, B. Barna, Z. Király and E. Páldi

Biotic and abiotic stresses induce increased formation of reactive oxygen species (ROS) through distinct pathways: pathogen infections activate specific ROS-producing enzymes (i.e. NADPH oxidase, cell wall peroxidases), which results in accumulation of cellular or intercellular ROS, such as superoxide or hydrogen peroxide. Abiotic stresses, on the other hand, cause elevated ROS production principally through an impairment of photosynthetic and respiratory electron transport pathways. Also, these two types of stresses have diverse effects on the antioxidant system of the plant. Results of experiments studying the interaction of abiotic and biotic stresses largely depend on the degree of the applied abiotic stress treatment, the compatible or incompatible host-pathogen interaction and the timing of inoculation in relation to the timing of a preceding abiotic stress treatment.

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Authors: J. Pintér, E. Kósa, G. Hadi, Z. Hegyi, T. Spitkó, Z. Tóth, Z. Szigeti, E. Páldi and L. Marton

The level of UV-B radiation reaching the surface of the earth is increasing due to the thinning of the ozone layer in the stratosphere over recent decades. This has numerous negative effects on living organisms.Some of the Hungarian inbred maize lines examined under the climatic conditions in Chile exhibited an unusually high proportion of pollen mortality, flowering asynchrony and barrenness. The evidence suggests that this can be attributed to the approx. 30% greater UV-B radiation in Chile.The investigation of this problem within the framework of abiotic stress breeding programmes is extremely important in the light of the global rise in UV-B radiation, which may make it necessary to elaborate a selection programme to develop inbred lines with better tolerance of this type of radiation.In the course of the experiment the same ten inbred lines, having different maturity dates and genetic backgrounds, were tested for five years in Chile and Hungary. The tests focussed on anthocyanin, a flavonoid derivative involved in the absorption of damaging UV-B radiation.Averaged over years and varieties, the total anthocyanin content in the leaf samples was significantly higher in Chile than in Hungary. This was presumably a response at the metabolic level to the negative stress represented by higher UV-B radiation.In the five early-maturing flint lines the anthocyanin contents were more than 45% greater than those recorded in Hungary. This suggests that these genotypes, originating from northern regions, were not sufficiently adapted to the higher radiation level. In these samples higher UV-B caused a sharp rise in the quantity of anthocyanin, which absorbs the dangerous radiation. In late-maturing genotypes the initial content of the protective compound anthocyanin was higher at both locations, so in these types the high radiation level was not a problem and did not cause any substantial change.Similar conclusions were drawn from the results of fluorescence imaging. The F440/F690 ratio indicative of the stress level was higher in late lines with a high anthocyanin content, good tolerance and good adaptability.

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