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Forage sorghum species, comprising grain and silage sorghum (S orghum bicolor) and sudangrass (Sorghum sudanense ), are considered the most drought-tolerant field crops in Hungary (Siklósiné Rajki, 1997). Several features, such as its tropical origin, deep voluminous roots, and thick waxy leaves and stem, enable the plants to survive periods with insufficient rainfall (Wall and Ross, 1970). Owing to its large roots, the crop shows wide adaptability to soils with moderate or low fertility. Though sorghum is used mainly for forage in Hungary, it is a very important source of bioenergy in other countries. Hungary lies in the northern part of the European sorghum belt, so the emphasis in the breeding programme is to develop early or mid-early forage sorghum hybrids adapted to Hungarian climatic conditions and soil properties, to introduce them into commercial production and to make them available for farmers.

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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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A field study conducted for two years at the Indian Agricultural Research Institute, New Delhi showed that intercropping potato with fenugreek is highly profitable and provides some in-season income to the potato growers. It also serves as an insurance against complete loss of income when the potato prices crash in the market.

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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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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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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 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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Summary  

The bioaccumulation of 198Au radionuclide, by Rhizoclonium riparium a member of Chlorophyceae has been studied. It has been observed that accumulation of gold on Rhizoclonium is almost pH independent and slightly higher at basic pH. Accumulation of gold was studied with 198Au radiotracer, 0.1, 1 and 5 ppm concentrations of gold. It has been concluded from the biochemical analysis that the gold accumulation is due to adsorption in the cellulose and not in protein, fat and carbohydrate. Accumulated gold was recovered when washed with conc. HNO3.

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