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  • Author or Editor: T. Janda x
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Low temperature is one of the most important limiting factors for plant growth throughout the world. Exposure to low temperature may cause various phenotypic and physiological symptoms, and may result in oxidative stress, leading to loss of membrane integrity and to the impairment of photosynthesis and general metabolic processes. Salicylic acid (SA), a phenolic compound produced by a wide range of plant species, may participate in many physiological and metabolic reactions in plants. It has been shown that exogenous SA may provide protection against low temperature injury in various plant species, while various stress factors may also modify the synthesis and metabolism of SA. In the present review, recent results on the effects of SA and related compounds in processes leading to acclimation to low temperatures will be discussed.

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Plants have developed various mechanisms to protect themselves against oxidative stress. One of the most important non-enzymatic antioxidants is ascorbic acid. There is thus a need for a rapid, sensitive method for the analysis of the reduced and oxidised forms of ascorbic acid in crop plants. In this paper a simple, economic, selective, precise and stable HPLC method is presented for the detection of ascorbate in plant tissue. The sensitivity, the short retention time and the simple isocratic elution mean that the method is suitable for the routine quantification of ascorbate in a high daily sample number. The method has been found to be better than previously reported methods, because of the use of an economical, readily available mobile phase, UV detection and the lack of complicated extraction procedures. The method has been tested on Arabidopsis plants with different ascorbate levels and on wheat plants during Cd stress.

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The aim of the present study was to find the best way of measuring the viability of root and leaf samples from various plant species (pea, wheat and maize) exposed to different concentrations of the heavy metal Cd. A comparison was made of three viability tests, namely electrolyte leakage measurements, and TTC and NBT reduction. The results suggested that electrolyte leakage was the most useful method for measuring leaf viability, being simple, fast, reliable and reproducible. The TTC reduction measurement proved the most useful for maize roots, while NBT reduction was the best method for detecting the viability of pea and wheat roots.

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The application of naturally occurring biologically active compounds could be an effective method to improve crop productivity under changing environmental conditions. In the present work the effects of priming maize seed with salicylic acid were tested on the grain yield under field conditions, and on the salicylic acid and polyamine metabolism under controlled environmental conditions. The field data suggested that the beneficial effects of pretreating maize seed with salicylic acid were mainly detectable in the yield in the case of early sowing dates. When young maize seedlings were exposed to low temperature stress, priming the seed with salicylic acid only modified the salicylic acid levels in the seed but not in the roots or leaves. The data suggested that salicylic acid was taken up by the seed and was then converted to bound forms. In contrast to salicylic acid, 5 days after sowing there was a substantial increase in the free form of ortho-hydroxy cinnamic acid in the seed, roots and leaves. Priming with salicylic acid also led to an increase in the putrescine content and a slight decrease in spermidine in the seed. The levels of putrescine, spermidine and spermine also increased in the roots of plants treated with salicylic acid under normal growth conditions. The results suggest that polyamines may also contribute to the stress tolerance of plants primed with salicylic acid.

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The research, carried out in the Martonvásár phytotron in 2007, was aimed at determining how the leaf water potential of maize hybrids produced in direct and reciprocal crosses, and thus possessing different levels of seed vigour, changed as the result of water withholding in the flowering phenophase. In the case of the silage maize hybrids Mv 290 and Lima it was found that seedling vigour influenced the plant height (measured at 30 days) of adult plants. Crosses produced on chilling-sensitive female genotypes (GL, AM, H29), such as the hybrids Káma, Maraton and Hunor, proved to be unambiguously stress-sensitive if water was withheld for more than six days. In all cases drought stress reduced the relative quantum efficiency, irrespective of the crossing combination.

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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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Phytotron experiments were conducted to examine the impact of elevated atmospheric CO2 level (750 μmol mol−1) on the drought tolerance of winter barley (Petra), durum wheat (Mv Makaroni) and spring oat (Mv Pehely) varieties. Under drought stress conditions, the durum wheat variety was found to be unaffected by CO2 enrichment, as neither the biomass or grain yield nor the antioxidant enzyme activities changed compared to those at ambient CO2. Despite the fact that the spring oat variety had similar grain yield loss due to drought at both CO2 levels, it exhibited reduced antioxidant enzyme activities under less severe drought, indicating a slightly increased tolerance to drought. Winter barley, which exhibited an extremely positive reaction to CO2 enrichment at the control water supply level, also showed increased drought tolerance in response to high CO2. It had low glutathione reductase, glutathione-S-transferase and ascorbate peroxidase activities even at the most severe drought stress levels, while it could also fully compensate for the negative effects of drought on biomass and grain yield parameters when grown at elevated CO2.

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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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Large numbers of wheat genotypes were grown under field conditions and screened for biotic stress tolerance and certain protective compounds. It was found that both the salicylic acid and polyamine contents of the investigated genotypes varied over a wide range, while the antioxidant enzyme activities showed a similar pattern in the different genotypes. In order to investigate stress-induced changes in salicylic acid and polyamine contents, samples were collected from plants artificially inoculated with leaf rust (Puccinia triticina), on which natural powdery mildew [Blumeria graminis (DC.) Speer f. sp. tritici Em. Marchal] infection also appeared. Biotic stress mostly resulted in elevated levels of total salicylic acid and polyamines in all the genotypes. The activities of various antioxidant enzymes showed similar changes after infection regardless of the genotype. The investigation was aimed at detecting a relationship between the level of stress tolerance and the contents of protective compounds, in particular salicylic acid and polyamines.

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The impacts of climate modification were examined in terms of changes in the stress tolerance of winter wheat varieties. The enzyme reactions of two winter wheat varieties to drought stress, simulated by water withholding in three different phenophases, were analysed in a phytotron experiment in the Centre for Agricultural Research, Hungarian Academy of Sciences. Plants were raised either at ambient CO2 level or at twice this concentration. The quantities of glutathione reductase (GR), glutathione-S-transferase (GST), catalase (CAT), guaiacol peroxidase (POD) and ascorbate peroxidase (APX) were determined from leaf samples collected at the end of the drought treatment.The results showed that antioxidant enzymes may help to counterbalance the reactive oxygen species induced by stress during various stages of the vegetation period. Although there were substantial differences in the changes induced in the activity of individual enzymes by modifications in environmental factors, this activity and its response to stress depended not only on these factors, but also on the developmental stage of the plant. Modifications in enzyme activity could indicate that enhanced CO2 concentration delayed the development of drought stress up to first node appearance, and stimulated antioxidant enzyme activity when drought occurred during ripening.

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