An Abandoned Copper Mining Site in Cyprus and Assessment of Metal Concentrations in Plants and Soil.

Mining is an important source of metal pollution in the environment and abandoned mines are extremely restricted habitats for plants. Some plant species growing on metalliferous soils around mine tailings and spoil-heaps are metal-tolerant and accumulate high concentrations of metals. In this investigation, we aimed to perform a research in the CMC-abandoned copper mining area in Lefke-North Cyprus to assess the recent metal pollution in soil and plant systems. We collected 16 soil samples and 25 plant species from 8 localities around the vicinity of tailing ponds. Some concentrations of metals in soil samples varied from 185 to 1023 mg kg(-1) Cu, 15.2 to 59.2 mg kg(-1) Ni, 2.3 to 73.6 mg kg(-1) Cd and metals for plants ranged from 0.135 to 283 mg kg(-1) Cu, 0.26 to 31.2 mg kg(-1) Ni, 0.143 to 277 mg kg(-1) Cd. Atriplex semibaccata, Acacia cyanophylla, Erodium spp., Inula viscosa, Juncus sp., Oxalis pes-caprea, Pistacia lentiscus, Senecio vulgaris and Tragopogon sinuatus accumulated higher concentrations. BCF for Atriplex semibaccata was found very high, for this reason this plant can tentatively be considered as a hyperaccumulator of Cu and Cd, but it needs further investigation for its potential in phytoremediation.

Regulation of Aspartate Kinase Isoenzymes in Barley Mutants Resistant to Lysine plus Threonine : Construction and Analysis of Combinations of the Lt1a, Lt1b, and Lt2 Mutant Genes.

Two homozygous mutant lines of barley (Hordeum vulgare L.) R3202 (Lt1b/Lt1b) and R3004 (Lt2/Lt2), are resistant to lysine plus threonine. They contain aspartate kinase isoenzymes with lost or decreased feedback sensitivity to lysine in either isoenzyme AKII (R3202) or isoenzyme AKIII (R3004). A homozygous double mutant line (Lt1b/Lt1b, Lt2/Lt2) has now been constructed that grows vigorously on 8 millimolar lysine, 8 millimolar threonine, and 1 millimolar arginine. Both AKII and AKIII from the double mutant have altered lysine sensitivities, identical to those previously observed in R3202 and R3004, respectively. Aspartate kinase activity in extracts of leaves, roots, and the maturing endosperm of the double mutant was much less sensitive to lysine inhibition than the enzyme in comparable extracts of the parent cv Bomi, suggesting that aspartate kinase is expressed in a similar manner in different tissues of barley.A further mutant, R2501, resistant to lysine plus threonine has now given rise to a homozygous line (Lt1a/Lt1a), which had previously not been possible. AKII isolated from the homozygous line was completely insensitive to 10 millimolar lysine; however, the combined action of 10 millimolar lysine and 0.8 millimolar S-adenosylmethionine inhibited it by 60%, demonstrating the retention of some of the regulatory characteristics of the wild type enzyme.

Lysine transport in two barley mutants with altered uptake of basic amino acids in the root.

Amino acid uptake was examined in two barley (Hordeum vulgare L.) mutants R906 and R4402 which had been selected as resistant to the lysine analog S-(2-aminoethyl)-cysteine. The mutants were found to be allelic by crossing and examination of F(1) and F(2) progeny. The mutant genes were designated aec1a and aec1b, respectively. The uptake of the basic amino acids lysine, arginine, and ornithine from 50 micromolar solutions was strongly decreased in roots of the mutants, whereas uptake of neutral and acidic amino acids was unaffected. The pattern of uptake of lysine over the range 10(-7) to 10(-2) molar was consistent with there being, principally, two uptake systems operating for basic amino acids in roots and that a low-concentration, high-affinity system is reduced or lacking in the mutants. The residual transport activity in the mutants had a different relative affinity for lysine and arginine to the wild-type system. Uptake of lysine by leaf slices was unimpaired in the mutants suggesting that the leaf uptake system is unaffected by the aec1 gene.

Feedback-insensitive aspartate kinase isoenzymes in barley mutants resistant to lysine plus threonine.

The regulatory properties of aspartate kinase (EC 2.7.2.4) and homoserine dehydrogenase (EC 1.1.1.3) in two barley (Hordeum vulgare L.) mutants resistant to growth inhibition by lysine plus threonine, Rothamsted (R) 3004 and R3202, were compared with those in the normal, sensitive parent line cv. Bomi. Three forms of aspartate kinase (AKI, AKII, AKIII) were chromatographically separated and were considered to represent at least three independently regulated isoenzymes. Aspartate kinase I was inhibited by threonine; AKII and AKIII by lysine or lysine plus S-adenosylmethionine. The characteristics of AKI were unchanged in the mutants. Aspartate kinase II and AKIII from Bomi were both inhibited by lysine and by lysine plus S-adenosylmethionine. Aspartate kinase II from mutant R3202 was altered in its properties such that it was insensitive to lysine or lysine plus S-adenosylmethionine; AKII from mutant R3004 did not differ in its properties from AKII of Bomi. The concentration of lysine required to give half maximal inhibition of AKIII from R3004 was ten times that required for AKIII of Bomi; AKIII from R3202 did not differ from that of Bomi in this regard. There was no change in the properties of homoserine dehydrogenase of the mutants as compared with that of Bomi. We conclude that the lt1 and lt2 loci code for structural genes for lysine- and lysine plus S-adenosylmethionine-sensitive aspartate kinase isoenzymes. The mutant genes Lt1b and Lt2 in R3202 and R3004 respectively code for feedback-desensitized isoenzymes. The presence of one of these is sufficient to allow the synthesis of methionine to overcome the growth inhibition by lysine plus threonine.

Threonine accumulation in the seeds of a barley mutant with an altered aspartate kinase.

Barley (Hordeum vulgare L.) mutants altered in the regulation of synthesis of aspartate-derived amino acids were sought by screening embryos for growth on a medium containing lysine plus threonine. One mutant, Rothamsted 2501, was selected with good growth. From the segregation of resistance in the following generations, it was concluded that the resistance was conferred by a dominant gene, Lt1. No homozygous Lt1/Lt1 fertile plants have been recovered. Partially purified aspartate kinase preparations from resistant and sensitive plants were separated on DEAE-cellulose chromatography into three peaks of activity (I, II, III) and the feedback regulatory properties of these peaks determined. These peaks are considered to be three isozymic forms of aspartate kinase, one predominantly sensitive to threonine and two sensitive to lysine or lysine plus S-adenosyl methionine. The feedback characteristics of one of the peaks of aspartate kinase activity from resistant plants were changed such that lysine was half-maximally inhibitory at 10 rather than 0.4 mM. Increases in te concentrations of the free pools of threonine (4x) and methionine (2x) were measured in young plants grown on a basal medium. Threonine in the soluble fraction of mature seeds from resistant plants was increased from 0.8 to 9.6% of the total threonine content. The total content of both threonine and methionine of the seeds was increased by 6% compared with grain of similar nitrogen content.

S-adenosylmethionine--a novel regulator of aspartate kinase.

Man derives 70% of his dietary requirements of protein directly from the grains of cereals and legumes. These sources are respectively deficient in lysine (and secondarily threonine) and methionine and much effort is being devoted to their improvement. All three amino acids are derived from aspartate via a common metabolic pathway (Fig. 1) in which the first reaction catalysed by aspartate kinase is a key regulatory step limiting their production. In microorganisms, regulation of aspartate kinase occurs by a variety of mechanisms, commonly involving feedback inhibition of one or more isoenzymes by Lys plus Thr, Lys alone or Thr alone. On the other hand, Met control of this step does not seem to conform to a general pattern. Met represses, but does not inhibit aspartate kinase II of Escherichia coli; in other species Met can enhance or modify the effects of Lys or Thr. Similarly, varied controls involving Lys and Thr have been reported for the enzymes from higher plants with only one report of an effect of Met. In contrast to these previous results, we suggest here that the methionine derivative (S)-S-adenosyl-L-methionine (AdoMet) is an important regulator of the Lys-sensitive aspartate kinase of higher plants, and that this regulatory mechanism is highly conserved. There is thus a major synergistic interaction of the two nutritionally deficient amino acids Lys and Met to inhibit their own syntheses at the primary regulatory step in the pathway.