COMPARISON OF SHOOT APEX DYNAMICS AND EARLY LEAF ONTOGENY IN TWO SPECIES OF SARACA (LEGUMINOSAE)

Shoot apices of Saraca indica produce adult leaves that have 4 to 6 pairs of leaflets, whereas those of S. bijuga usually have only 2 pairs. In both species one leaflet pair is found during the juvenile phase. Juvenility lasts many plastochrons in S. bijuga but is restricted to a few in S. indica. The shoot apical meristems of these two taxa are similar in structure, cell number, and cell size; however, the shoot apex of Saraca bijuga is slightly more stratified, having 2–3 tunica layers as opposed to 1–2 in S. indica. For most of the plastochron the apical meristem in both species is situated laterally at the base of the most recently formed leaf. A newly forming primordium and its internode shift the apical meristem upward unilaterally; the meristem passes through a brief apical dome stage and becomes positioned 180° from its origin at the beginning of the plastochron. Hence, there is a true pendulum meristem in both species. In S. bijuga the maximum length of the youngest leaf primordium, just prior to the formation of its successor, is twice that of S. indica. The internodes immediately below the shoot apex and the axillary buds develop more rapidly in S. bijuga than in S. indica. It is suggested that the bijugate leaf of S. bijuga represents a case of neoteny in plants.     

Effects of Lead on the Activities of Antioxidant Enzymes in Watercress, <Emphasis Type="Italic">Nasturtium officinale</Emphasis> R. Br.

The aim of the present study is to evaluate the oxidative effects of lead with increased concentrations by the determination of antioxidant enzyme activities (superoxide dismutase (SOD), catalase (CAT), glutathione reductase (GR), and ascorbate peroxidase (AP)) and lipid peroxidation levels in the stem and leaves of watercress (Nasturtium officinale R. Br.) which was exposed to lead acetate, Pb (CH₃COOH)₂ regime with concentrations of 0, 50, 100, 200, 250, and 500 mg/L Pb in a hydroponic culture. After 14 days, accumulation of lipid peroxidation in stems and leaves and changes in activity of antioxidant enzymes were determined spectrophotometrically. The maximum accumulation was observed in the highest concentration group. In this group, lipid peroxidation levels were three times higher than the control group in the stem and leaves. The highest induction in SOD and GR activities were determined at 200 mg/L Pb group in stem, whereas CAT and AP activities were higher than other groups at the concentration of 250 and 100 mg/L Pb, respectively. The increase in CAT activity was found to be greater than GR, SOD, and AP activities in stems of watercress under Pb treatment. Both lead accumulation and antioxidant enzyme responses were higher in stems than in leaves. The results of the present study suggested that the induction in antioxidant responses could be occurring as an adaptive mechanism to the oxidative potential of lead accumulation.     

Nephrotoxicity of simultaneous exposure to mercury and uranium in comparison to individual effects of these metals in rats

Both inorganic mercury and uranium are known nephrotoxicants in mammals. In this study, the renal toxicity of a concurrent exposure to inorganic mercury and uranium was compared with the nephrotoxic effects of the individual metals in a rat model. Eight groups of rats, 10 animals per group, were subcutaneously given a single administration of mercuric chloride (HgCl₂, 0.34 mg/kg and 0.68 mg/kg), uranyl acetate dihydrate (UAD, 2.5 mg/kg and 5 mg/kg), or combinations of both compounds at the same doses. A ninth group of rats received sc injections of 0.9% saline and was designated as the control group. Necrosis of proximal tubules, which was observed in all experimental groups, was the most relevant morphologic abnormality. Marked changes, which were remarkably greater than those induced by the individual elements, were noted in some urinary parameters in the groups concurrently exposed to HgCl₂ and UAD. It could be an indicator of a synergistic interaction between mercury and uranium. In contrast, compared with the urinary levels found after individual administration of the highest doses of mercury and uranium, significant reductions in the urinary concentrations of these elements were noted following simultaneous exposure to both metals. At these doses, the reduction in the urinary metal excretion was also accompanied by significant decreases in the renal content of mercury and uranium. Whereas the results of some parameters pointed out a possible synergistic interaction between mercury and uranium, other measures hinted that an antagonistic interaction between these elements is also present.     

Studies on the mercury volatilizing enzymes in nitrogen-fixing Beijerinckia mobilis

Beijerinckia mobilis KDr₂, a broad-spectrum, mercury-resistant nitrogen-fixing organism, possesses multiple metal-resistance properties. Mercuric reductase and organomercurial lyase activities of this bacterial strain were determined using different mercury compounds and heavy metal salts of copper, nickel, cobalt, cadmium, silver, zinc, lead and arsenate as inducers and substrates. Mercuric reductase was partially purified and the effect of some enzyme inhibitors and heavy metal ions on the enzyme activity was studied. The enzyme activity was completely inhibited by CdCl₂, Bi(NO₃)₃ and KCN at 10^-5 M and by AgNO₃, CoCl₂ and CuSO₄ at 10^-4 M.     

Acid phosphatase and invertase activities of <Emphasis Type="Italic">Aspergillus niger</Emphasis>

Aspergillus niger is widely used as an enzyme source in industries. Considering its enzymic potential, A. niger was studied for its acid phosphatase (EC 3.1.3.2, orthophosphoric monoester phosphohydrolase), and invertase (EC 3.2.1.26, β-fructofuranoside fructohydrolase) activity in defined media supplemented with 1%, 3%, or 5% sucrose concentrations. Both these enzymes play a key role in phosphate and carbon metabolism in plants, animals, and microorganisms and hence are interesting from the standpoint of biotechnological applications. Ontogenic changes in extracellular, cytoplasmic, and wall-bound enzyme activities of A. niger were studied. Growth in terms of fresh weight showed inverse correlation with pH. At higher pH values, both enzyme activities were higher in the medium supplemented with low sucrose concentration. It was observed that the more the fresh weight of fungi decreased, the greater was the enzyme activity observed. It is suggested that these enzymes may participate in autolysis of fungi and, on the other hand, could prove to be a potential source of industrial application and exploitation.     

The endoglucanase from <Emphasis Type="Italic">Bacillus</Emphasis><Emphasis Type="Italic">subtilis</Emphasis> BEC-1 bears halo-tolerant,acidophilic and dithiothreitol-stimulated enzyme activity

A Bacillus subtilis strain BEC-1 demonstrating high carboxymethylcellulose-degrading activity was isolated from the forest soil sample. In order to characterize the biochemical specialty of its cellulase, the endoglucanase gene egl173 was cloned from this strain and was expressed in Escherichia coli. The gene encoded a protein of 499 amino acids with a molecular weight of 64 kDa. The purified Egl173 could hydrolyze both soluble and insoluble celluloses with distinct activities. This enzyme showed the highest enzyme activity at pH 4, maintained at least 85% activity in the pH range of 3–7, displayed maximum activity at 60°C and was highly stable between 30 and 60°C. It was found that this endoglucanase was increasedly active and retained its high stability after incubation with 5 M NaCl or 3 M KCl for 24 h. Furthermore, after incubation with 10 mM of dithiothreitol, the enzyme activity was significantly enhanced (125% of the control level). In the presence of diverse metal ions (except mercury and manganese cations), organic solvents, surfactants (except SDS) and chelating agent, this enzyme kept more than 85% active. This halo-tolerant, acidophilic and highly stable endoglucanase is prospectively to be exploited as the advanced enzymatic product for diverse industrial applications.     

Efficiency of using green algae as biological controllers against toxic algal taxa in cultured Nile tilapia Oreochromis niloticus,based on histopathological examinations

The incidence of harmful cyanobacterial blooms in surface waters has increased in frequency and outbreaks have become more severe. This research aimed at studying the effect of a culture of two green algal species as biological control of the growth of toxic blue-green algae. Nile tilapia of an initial mean weight of 55 g fish^?1 (SE 5) were used for each of four treatments in triplicate. All algal seedings were done at 4 × 10³ cells ml^?1. Treatment I (untreated) served as a control, Treatment II was seeded with Microcystis aeruginosa, Treatment III was seeded with green algae Chlorella ellipsoidea and Scenedesmus bijuga, and Treatment IV was seeded with a mixture of M. aeruginosa and C. ellipsoidea and S. bijuga. After 10 days, Treatment IV showed 3.4% viable cell survival, compared to 35% and 55% in Treatments II and III, respectively. Histopathological examination revealed mild degenerative changes and focal necrosis, as well as a depletion of haematopoietic tissues in Treatment IV compared to Treatment II. These findings suggest the efficacy of C. ellipsoidea and S. bijuga in controlling the growth of M. aeruginosa and minimising its side effects on cultured Nile tilapia.     

Purification and properties of glutamine synthetase from the archaebacterium Halobacterium salinarium

Glutamine synthetase (GS) was purified to electrophoretic homogeneity from the halophilic archaebacterium Halobacterium salinarium. The enzyme was purified 300-fold to homogeneity with 30% yield. By gel filtration and SDS gel electrophoresis, it was shown that the enzyme has a native molecular weight of 495,000 and a subunit molecular weight of 62,000. This indicates an octameric quaternary structure. The amino acid composition and the isoelectric point of 4.9 are similar to other GSs. The enzyme shows highest stability in 4 M NaCl or KCl and at temperatures up to 45°C. Lower salt concentrations or higher temperatures lead to rapid and irreversible denaturation. By low concentrations of Mg²⁺ or Mn²⁺, the salt dependence was decreased and the thermostability increased. Mg²⁺ or Mn²⁺ are essential cofactors. The two resulting activities show differences in pH and salt concentrations required for optimal activity, different K _m-values and different sensitivity to inhibition by amino acids. The enzyme is not adenylylated like the GS from some eubacteria but cytidylylated. The covalently bound CMP increases Mn²⁺-and Mg²⁺-dependent activities at a different extent.     

Ectomycorrhizas of <Emphasis Type="Italic">Coltricia</Emphasis> and <Emphasis Type="Italic">Coltriciella</Emphasis> (Hymenochaetales,Basidiomycota) on Caesalpiniaceae,Dipterocarpaceae and Myrtaceae in Seychelles

Ectomycorrhizal fungi, especially basidiomycetes, have repeatedly evolved from saprotrophic ancestors. Using rDNA internal transcribed spacer and large subunit sequences, we demonstrate that four species of Coltricia and Coltriciella form ectomycorrhiza with the native Vateriopsis seychellarum (Dipterocarpaceae) and Intsia bijuga (Caesalpiniaceae) as well as the introduced Eucalyptus robusta (Myrtaceae) in Seychelles. Coltricia and Coltriciella species share a thin, orange-brown to dark brown mantle and extremely thick, clampless hyphae. Phylogenetic analyses placed Coltriciella monophyletic within Coltricia. This study provides further evidence that fruiting habit on dead wood does not indicate saprotrophic lifestyle.     

Effect of mercury nitrate on the histochemical activity of some dehydrogenases in primary cultures of rat kidney tubular cells

Direct effect of sublethal and lethal doses of mercury nitrate on histochemical activity of G6PDH, LDH and SDH was investigated in primary cultures of rat tubular cells. Enzyme activities were studied histochemically after administration of mercury nitrate for periods extending from 5 min. to 24 hrs and also after 2,3,4 and 5 following days. The sublethal doses of mercury nitrate containing 1 microgram and 5 microgram of mercury were found to decrease histochemical activity of the studied dehydrogenases as early as 10 and 15 minutes. Their inhibitory effect was much stronger after 24 h and depended on the dose of mercury compound. The lethal doses of mercury nitrate containing 15 microgram and 20 microgram of mercury depressed the activity of dehydrogenases within 5 min. after administration. The loss of enzyme activities usually preceded the appearance of necrotic signs in the cultured cells. It was also found that the cultured cells of kidney tubules treated with sublethal doses of mercury nitrate were usually able to regain the normal level of the enzymic activity within 2-5 days.     

Soft-tissue accumulation of lead in the blue tilapia,Oreochromis aureus (steindachner), and the modifying effects of cadmium and mercury

The interaction of mercury and cadmium with lead was investigated by exposingOreochromis aureus to two heavy metals simulataneously. The chronic accumulation prolife of lead was determined by analyzing the liver, brain, gill filaments, intestine, caudal muscle, spleen, trunk kidney, and gonads following exposure to lead alone and in mixtures with mercury and cadmium. Nominal exposure concentrations of lead were 0.05, 0.10, 0.50, and 1.00 mg/L. Mixtures of lead (0.50 or 0.05 mg/L) with cadmium (0.05 mg/L) and lead (0.50 or 0.05 mg/L) with mercury (0.05 mg/L) were also used. Following 140 d of exposure to lead, the highest concentrations of lead consistently accumulated in the trunk kidney. The concentration of lead in the kidney was decreased by coexposure to mercury or cadmium, but increased in the muscle and liver. Under all exposure regimes, the median concentration of lead in the muscle exceeded safety levels recommended for human consumption. In a food fish, such asO. aureus, a knowledge of toxic metal accumulation patterns is of great importance.     

Phycobiliproteins from <Emphasis Type="Italic">Pseudanabaena tenuis</Emphasis> rich in c-phycoerythrin protect against HgCl<Subscript>2</Subscript>-caused oxidative stress and cellular damage in the kidney

Our objective was to study if the phycobiliproteins of the cyanobacterium Pseudanabanea tenuis rich in phycoerythrin protect renal cells against mercury-caused oxidative stress and cellular damage in the kidney. We used 40 male mice that were assigned into five groups: a control group that received phosphate buffer (PB) and saline and four treatment groups which received either PB+HgCl₂, PB+phycobiliproteins, or HgCl₂+phycobiliproteins. The kidneys of the mice were used to determine lipid peroxidation and quantification of reactive oxygen species, oxidized glutathione, and peroxidase activities (catalase and glutathione peroxidase) and were also examined histologically. Our results demonstrated that HgCl₂ causes oxidative stress and cellular damage and that all doses of phycobiliproteins prevented the increase of oxidative markers and partially protected against HgCl₂-caused cell damage. This is the first report which applied phycobiliproteins of P. tenuis rich in c-phycoerythrin, like antioxidants against mercury chloride-caused oxidative stress and renal damage.     

Lead,mercury, and certain nutrient elements in ulva lactuca (linnaeus) from Ras Beirut,Lebanon

Collections of Ulva lactuca (Linnaeus) at nine locations along the coast of Ras Beirut, Lebanon were analysed for lead, mercury, phosphate, calcium, magnesium, iron, copper, and zinc. Low lead concentrations, the same in all samples, could possibly indicate that U. lactuca has some means by which lead uptake and toxicity can be controlled. Phosphate levels may be a contributing factor to this process.Concentrations of all other elements seemed relatively uniform with few exceptions. This suggests that U. lactuca is subject to similar environmental conditions and element exposure at each of the collecting sites and might be capable of maintaining biochemical stability under high levels of stress.Further studies of toxic and nutrient elements as to their individual and combined effects in U. lactuca are needed.c/o Sturdy Memorial Hospital, Attleboro, Massachusetts U.S.A.     

Changes in germinability,lipid peroxidation,and antioxidant enzyme activities in pear stock (<Emphasis Type="Italic">Pyrus betulaefolia</Emphasis> Bge.) seeds during room- and low-temperature storage

The aim of this study was to determine if loss of germinability in Pyrus betulaefolia seeds stored at 4°C and at room temperature is associated with a loss of membrane lipid peroxidation or changes in antioxidant enzyme activities. The results indicated that germination percentage clearly decreased when seeds were stored at room temperature rather than at 4°C from 6 to 12 months. Room-temperature storage of the pear stock seed for 12 months decreased germination to 15.52%, but germination percentage was not changed when seed was stored at 4°C for 12 months. MDA, a marker for membrane lipid peroxidation, increased significantly under room-temperature storage conditions. Antioxidant enzyme (SOD, POD, and CAT) activities were a good indicator of germination percentage in pear stock seeds. Antioxidant enzyme activities of pear stock seeds at 4°C were higher than antioxidant enzyme activities in seeds stored at room temperature from 6 to 12 months. Antioxidant enzyme activities of the pear stock seed decreased markedly under conditions of room-temperature storage from 6 to 12 months. The results of this study showed that long-term room-temperature storage was detrimental for maintaining the vigor of P. betulaefolia seeds. The mechanisms responsible for this outcome are a higher level of membrane lipid peroxidation and a lower level of activity of antioxidant enzymes.     

Porphyrin metabolism in lead and mercury treated bajra (Pennisetum typhoideum) seedlings

Lead and mercury inhibited porphyrin biosynthesis significantly in the germinating seeds of bajra (Pennisetum typhoideum). Both 5-aminolevulinic acid dehydratase and porphobilinogen deaminase activities were inhibited by these metals. A comparative study of the inhibition of these two enzymes under invivo andin vitro conditions showed that 5-aminolevulinic acid dehydratase is the major site of action of heavy metals in porphyrin biosynthesis. Further, over-all production of porphyrinsviz., protoporphyrin-IX, Mg-protoporphyrin (ester) and protochlorophyllide was repressed by lead and mercury in both light and dark grown seedlings. Similarly, chlorophylla and chlorophyllb and total chlorophyll contents in dark-grown seedlings were also significantly decreased, suggesting the impairment of chlorophyll biosynthesis by lead and mercury in germinating seedlings.     

Induction of micronuclei and sister chromatid exchange in bone-marrow cells and abnormalities in sperm of Algerian mice (Mus spretus) exposed to cadmium, lead and zinc

As a consequence of human activities, large amounts of cadmium, lead and zinc are released in the environment, often simultaneously. The aim of this study was to investigate under experimental conditions the DNA damage induced in Algerian mice (Mus spretus) exposed to cadmium (Cd), lead (Pb) and zinc (Zn) separately, or in selected combinations. Three cytogenetic end points were considered: the frequencies of micronucleated cells (MN) and sister chromatid exchange (SCE) in the bone marrow and the frequency of sperm abnormalities. Mice were treated by intraperitoneal (i.p.) injections with 5 or 10 doses of aqueous solutions of cadmium acetate, lead acetate and zinc acetate in concentrations corresponding to 1/10 of the LD50, respectively, 21.5, 0.46 and 1.5 mg/kg bw. The control groups were injected in the same way with distilled water.With only one exception (Cd + Zn group treated with 5 doses), the results show a significant increase of MN in all groups for both treatments (5 and 10 doses). Similarly, the results concerning the SCE revealed a statistically significant increase in all treated animals, with the exception of the Zn group treated with 5 doses. The number of sperm abnormalities was significantly higher in animals treated with 5 doses, except in the group Pb + Zn. In animals treated with 10 doses the number of sperm abnormalities was always statistically higher compared with controls.This study indicates that cadmium, lead and zinc can induce MN, SCEs and sperm abnormalities in Algerian mice and that the clastogenic potential is dependent on the time of exposure and the interaction between the three elements, confirming the environmental damage that may result from the simultaneous action of several metals. Most relevant is the toxic potential for Zn, related with the dose, which may compromise its protective effect against other metal contaminations, such as cadmium.     

Levels of toxic and essential elements in arctic fox in Svalbard

Concentrations of cadmium, mercury, lead, arsenic, selenium, copper, zinc, manganese and iron in liver, and cadmium in kidneys, were analysed in 95 carcasses of arctic fox (Alopex lagopus) caught in Svalbard during three winter seasons from 1984 through 1986. The hepatic concentration ranges of cadmium, mercury, lead and arsenic were 0.1–2.4, 0.01–2.2, < 0.5–2.9 and 0.01–1.3 g·g^–1 WW, respectively. The range of cadmium concentration in the kidneys was from 0.2 to 13 g·g^–1 WW. Cadmium and mercury concentrations were higher in adult animals than in juveniles. The average concentrations of cadmium and lead were similar to recently published levels in polar bear from Svalbard, but the mercury concentrations were lower. Significant geographical differences were observed between trapping areas. Foxes caught north of Isfjorden had lower levels of liver iron and higher levels of all other elements analysed than those caught south of Isfjorden. The recorded concentrations of heavy metals indicate a moderate degree of exposure, which most likely is of natural origin.Gunnar Norheim died January 9, 1991     

Effect of α-Naphthalene- and α-Naphthoxyacetic Acid on the Activity of Certain Enzymes of Atropa belladonna cv. lutea Cells in Suspension Culture

The growth of Atropa belladonna cv. lutea Döll cells and the activities of several enzymes were studied as a function of time in suspension cultures without added auxin, with α-naphthaleneacedc acid (NAA) and with α-naphthoxyacetic acid (NOA). The growth curves were rather similar and therefore easy to compare. The enzyme activities (per mg dry weight of culture) were distinctly higher in cultures grown with NAA than in the other two treatments, in which root formation was common. In some cases the enzyme activities were lower in cultures with NOA than in the control series but usually the curves were quite parallel. Promotion of enzyme activities by NAA (aldolase, aminopeptidase, gluta-mate: oxaloacetate transaminase) was clearest in the beginning of the phase of rapid cell division (6-day-old culture). These three enzymes reach their maxima at this stage of growth in the other series as well. Ribonuclease activity increased in the stationary phase cells (13 and 19 days) with NAA but with the other treatments the level of this activity was relatively stable. Peroxidase and phosphatase did not show any characteristic maxima, glutamate: pyruvate transaminase activity was low and no amylase activity could be demonstrated. The results indicate that synthetic plant growth substances can regulate the physiological state of a tissue by causing alterations in enzyme activities, but their action is clearly specific.     

Effects of heavy metals on growth and ultrastructure ofChara vulgaris

Summary The toxicity of some heavy metals to the common macrophytic freshwater algaChara vulgaris was studied under laboratory conditions. For experiments, apical tips of algae containing two internodes were cultivated for fourteen days in the presence of various concentrations of cadmium, mercury or lead (as triethyl lead or lead nitrate). Fifty percent growth inhibition occurred with concentrations of 8.5×10^–8 M (9.5 ppb) cadmium, 7.5×10^–7M (150ppb) mercury, 1.6×10^–6 M (330ppb) organic lead or 4× 10^–5 M (8000 ppb) inorganic lead. Sublethal concentrations of these metals caused alterations in the fine structure of internodal cells which turned out to be at least partly metal-specific or in the case of lead, the effects depended on whether the lead was ionic or organically bound. Cadmium and inorganic lead induced disorders of cell wall microfibrils which resulted in local wall protuberances. Mercury affected the chloroplasts which mostly showed considerably increased grana stacks. In addition, mercury caused a dilation of the endoplasmic reticulum and of the mitochondrial tubuli. Organic lead damaged the membrane system of chloroplasts; sheet- or tubule-like thylakoids were disarranged and showed whorl-like structures. At higher concentrations of organic lead, tubular invaginations of the plasmalemma (charasomes) disappeared. The fine structure of nuclei was not altered by any of the metals.