Light‐induced changes in rabbit pineal gland n‐acetyltransferase activity

N‐acetyltransferase (NAT) activity was determined in different ages of New Zealand White rabbit pineal gland using 2‐aminofluorene and p‐aminobenzoic acid as substrates and it was assayed by high pressure liquid chromatography. Rabbits of different ages were either sacrificed during the light phase, exposed to darkness or light for 1 min during the dark phase of the lighting cycle, returned to their cages in darkness for 30 min and then sacrificed. Pineal gland NAT activity in animal nocturnally exposed to 1 min of light was inhibited in animals 1 ‐day‐old of age. Nocturnal light exposure did not inhibit enzyme activity in 1‐day‐old rabbit, even though these animal displayed clear light : dark differences in pineal gland NAT activity. Nocturnal light exposure also did not inhibit night time levels of NAT activity in 1‐day‐old animals who had been bilaterally enucleated. The result suggested that this effect is retinally mediated. Pre‐treatment of 1‐day‐old and 60‐day‐old animals with the isoproterenol (beta‐noradrenoreceptor agonist drug), prevented the nocturnal light‐induced inhibition of NAT activity. The different sensitivity of 60‐day‐old and 1‐day‐old animals to different illuminances or durations of nocturnal light exposure, was that the duration or intensity of light exposure was enable to inhibit nocturnal NAT activity. The NAT activity was at least 3.2‐ to 4.6‐fold greater in 1‐day‐old rabbits compared to 60‐day‐old rabbits. Kinetic constants for arylamine NAT activity in pineal gland from rabbits were determined. K_m and F_max values for 2‐aminofluorene were 2.6‐fold higher for light exposure than for no light exposure rabbits. This is the first demonstration of the retina‐pineal gland pathway appears light‐induced changes in pineal glands of animals in 1‐day‐old of ages or older; but this pathway does not function in 60‐day‐old rabbits like manner in 1‐day‐old rabbits.     

Paeonol promotes arylamine N‐acetyltransferase activity in human bladder tumor cells

Paeonol was used to determine effects of arylamine N‐acetyltransferase (NAT) activity in human bladder tumor cells. The NAT activity was measured by high performance liquid chromatography assaying for the amounts of N‐acetyl‐2‐aminofluorene (2‐AAF) and N‐acetyl‐p‐amino‐benzoic acid (N‐Ac‐PABA) and remaining 2‐aminofluorene (2‐AF) and p‐aminobenzoic acid (PABA). The NAT activity in human bladder tumor cells was promoted by paeonol in a dose‐dependent manner, i.e. the higher the concentration of paeonol, the higher the promotion of NAT activity. The data also indicated that paeonol increases the apparent values of K_m and K_max from human bladder tumor cells in cytosols and intact cells. This report is the first demonstration to show paeonol did promote human bladder tumor cell NAT activity.     

Kinetics of acetyl CoA: Arylamine N‐acetyltransferase from rapid and slow acetylator fish tissues

N‐acetyltransferase (NAT) activity was determined in 100 fish (Oreochromis mossambicus) livers using 2‐aminofluorene and p‐aminobenzoic acid as substrates. Overall, the liver NAT activity of the 50 females was higher than the liver NAT activity of the 50 males. The activities (mean ± SD) of NAT from kidney, blood, intestine, and liver of males was 0.42 ± 0.11, 0.12 ± 0.03, 0.12 ± 0.08, and 1.56 ± 0.54 nmol/min/mg protein for the acetylation of 2‐aminofluorene and 0.36 ± 0.09, 0.09 ± 0.01, 0.11 ± 0.04, and 0.46 ± 0.15 nmol/min/mg protein for the acetylation of p‐aminobenzoic acid. In kidney, blood, intestine, and liver from female fish, the activities obtained were 1.60 ± 0.12, 0.35 ± 0.07, 0.15 ± 0.09, and 1.89 ± 0.50 nmol/min/mg protein for 2‐aminofluorene and 0.95 ± 0.11, 0.27 ± 0.03, 0.13 ± 0.09, and 0.57 ± 0.12nmol/min/mg protein for p‐aminobenzoic acid. Kinetic constants for arylamine N‐acetyltransferase activity in kidney, blood, intestine, and liver from fish with rapid, intermediate, and slow acetylator activity were determined. Apparent K _m and V _max values for 2‐aminofluorene were 5.5 and 7‐fold higher for liver than for the other tissues. Apparent K _m and V _max values for p‐aminobenzoic acid were 3.5 and 4.7‐fold higher for liver than for the other tissues. Based on the 2‐aminofluorene NAT activity of liver, there appears to be a polymorphism in NAT activity with 16 rapid, 28 intermediate, and 56 slow acetylators among the 100 fish assayed. This is the first demonstration of acetyl CoA: arylamine N‐acetyltransferase activity in fresh water fish and could lead to the development of a fish model for monitoring the effect of pollution of water environments on native species.     

Effects of the Ellagic acid on the N‐Acetyltransferase activity and Acetylation of 2‐aminofluorene in the rat

The effects of the ellagic acid on the in vitro and in vivo acetylation of 2‐aminofluorene were investigated in male Sprague‐Dawley rats. For in vitro examination, cytosols with or without ellagic acid co‐treatment showed different percentage of 2‐aminofluorene acetylation. For in vivo examination, pre‐treatment of male rats with ellagic acid (10 mg/kg) 24h prior to the administration of 2‐aminofluorene (50 mg/kg) resulted in a 26% and 29%, respectively, decrease in the urinary and fecal recovery of N‐acetyl‐2‐aminofluorene, and a 37% decrease in the metabolic clearance of 2‐aminofluorene to N‐acetyl‐2‐aminofluorene. This is the first demonstration that ellagic acid decrease the N‐acetylation of carcinogens in vitro and in vivo.     

Effects of ellagic acid on arylamine N‐acetyltransferase activity in human colon tumor cells

The inhibition of arylamine N‐acetyltransferase (NAT) activity by ellagic acid was determined in a human colon tumor (adenocarcinoma) cell line. Two assay systems were performed, one with cellular cytosols (9000g supernatant), the other with intact colon tumor cell suspensions. The NAT activity in a human colon tumor cell line was inhibited by ellagic acid in a dose‐dependent manner in both types of examined systems: i.e. the greater the concentration of ellagic acid in the reaction, the greater the inhibition of NAT activities in both systems. The data also indicated that ellagic acid decreased the apparent K _m and V _max of NAT enzymes from human colon tumor cells in both the systems examined. This report is the first demonstration which showed ellagic acid affect human colon tumor cell NAT activity.     

Metsulfuron‐methyl soil persistence and mobility in winter wheat and following green manure crops

A procedure has been developed for the analysis of metsulfuron‐methyl in the soil of field crops. The soil extracts are cleaned by repeated TLC, and metsulfuron‐methyl is simultaneously separated from its soil metabolites. Metsulfuron‐methyl is transformed by diazomethane into its N,N ‘‐dimethyl derivative which in the GC (electron capture detection) and GC‐MS apparatus is transformed into a benzisothiazole compound which is measured with great sensitivity. The sensitivity limit is 0.3 μg metsulfuron‐methyl kg^‐1 dry soil. The results of the chemical analyses are confirmed by bioassays using sugar beet as test plant. Metsulfuron‐methyl was measured in the soil of two winter wheat crops after post‐emergence application in the spring of 6 g metsulfuron‐methyl ha^‐1. In the 0–8 cm surface soil layer, the metsulfuron‐methyl soil half‐life was 78 days in 1997, and 67 days in 1998. During crop, metsulfuron‐methyl remained in the 0–8 cm surface soil layer. There, it was at a maximum concentration and herbicide efficiency in a 2 cm‐thick soil layer. This maximum concentration soil layer progressively moved down during crop, attaining the 4–6 cm surface soil layer at crop end. After the winter wheat harvest at the end of July, and the rotary‐tilling of the 0–10 cm surface soil layer before sowing of the green manures, 27% of the metsulfuron‐methyl initial dose still remained in the 0–10 cm surface soil layer. This residue progressively disappeared, and was no more detected at the middle of November. It had no, or only very low inhibiting effect on the growth of the green manures. Thus there is no concern about the possible phytotoxicity of persistent metsulfuron‐methyl soil residues towards the following crops, when metsulfuron‐methyl is applied at the rate of 6 g a.i.ha^‐1.     

Antagonistic potential of fluorescent pseudomonads and control of charcoal rot of chickpea caused by Macrophomina phaseolina

The effectiveness of plant growth promoting rhizobacteria especially Pseudomonas fluorescens isolates were tested against charcoal rot of chickpea both in green house as well as in field conditions. Most of the isolates reduced charcoal rot disease and promoted plant growth in green house. A marked increase in shoot and root length was observed in P. fluorescens treated plants. Among all the P. fluorescens isolates Pf4-99, was found most effective in the improvement of chickpea crop in green house as well as in field. Pf4-99 effectively promoted plant growth and produced indole acetic acid in culture medium. This isolate also inhibited the mycelial growth of the M. phaseolina under in vitro conditions and reduced the disease severity Potential isolate (Pf4-99) also significantly increased the biomass of the chickpea plants, shoot length, root length and protein content of the chickpea seeds. A part from these, the total number of seeds per plant and their weight were also enhanced. The colonization of Pf4-99 reduced the incidence of seed mycoflora by which indirectly enhanced the seed germination and vigour index of seedlings. The observations revealed that isolate Pf4-99 is quite effective to reduce the charcoal rot disease both in field and greenhouse, and also increases seed yields significantly Therefore, this isolate appears to be an efficient biocontrol agent against charcoal rot disease as well as yield increasing rhizobacterium.     

In vitro Methylation of Arsenite in Flemish giant rabbit Cytosol

The formation of ⁷⁴As‐monomethyIarsonic acid and ⁷⁴As‐dimethylarsinic acid from carrier‐free radiolabelled ⁷⁴As‐arsenite was evaluated in an assay mixture containing 17.6% liver cytosol from the Flemish Giant rabbit. The optimal incubation temperature and pH were respectively, 39°C and 7.6. After a 2h incubation about 90% of ⁷⁴As was protein bound. Protein bound ⁷⁴As was released by hot 2 M HNO₃ (1 min, 110°C). The treatment did not destroy methylated As‐species. Up to 70% of the carrier‐free ⁷⁴As‐arsenite was methylated. Liver cytosol was stored, without loss of activity, in liquid nitrogen in the presence of 2 mM glutathione. The optimal s‐adenosyl‐methionine concentration was 1.7mM. Formation of ⁷⁴As‐monomethylarsonic acid and ⁷⁴As‐dimethylarsinic acid increased up to a glutathione concentration of respectively 10 and 20 mM. Methylation also went through in the presence of other reducing agents and proved to be ATP dependent.     

Dry deposition and particle size distributions of nitrate and sulfate in ambient air

This study reports the dry deposition pollutants of anion species (NO₃ ^‐ and SO₄ ^‐2) in the Ping Tung City of Southern Taiwan. Several deposition properties are discussed in this paper. It included dry deposition flux, anion species size distribution and deposition velocities. Noll Rotary Impactor (NRI) and Microorifice Uniform Deposit Impactor (MOUDI) were used to collect ambient air coarse and fine particulate. Dry deposition plate was applied to collect particle deposition flux. Dionex 2000i/SP Ion Chromatography equipped with 4 mm AG4A‐SC and AS4A‐SC column was employed to analyze the anion species. The eluent solution is 1.8 mM sodium carbonate/1.7 mM sodium bicarbonate. The measured dry deposition flux of nitrate ranged from 0.63 to 3.96 mg/m²‐day and averaged 2.12 mg/m²‐day, while the measured dry deposition of sulfate ranged from 1.17 to 9.53 mg/m²‐day and averaged 3.92 mg/m²‐day. The particle size distribution of nitrate has bimodal particle size distributions. However, the sulfate displayed uniform particle size distribution for all four sampling sites. Mean cumulative fraction (F%) of nitrate in the particle size range below 1, 2.5, 10 and 25 μm, in sequence, were 34.6%, 60.9%, 91.0% and 97.6%, respectively. However, the mean F% of sulfate in the particle size range below 1, 2.5, 10 and 25 um, in sequence, were 57.3%, 82.6%, 90.3% and 98.0%, respectively. The sulfate has more F% in the submicron particles. The mean MMD _o of nitrate and sulfate are 2.35 and 0.87 μm, respectively. The mean dry deposition velocities of nitrate and sulfate are 0.45 and 0.38 cm/sec, respectively.     

Effects of lead and selected pyrethroids/piperonyl butoxide alone and in combination on Na,K‐ATPase

In vitro effects of Pb²⁺, the pyrethroid insecticides cypermethrin, fenvalerate and the syner‐gist piperonyl butoxide on sodium‐potassium‐activated adenosine triphosphatase (Na,K‐ATPase) from dog kidney were determined. Pb²⁺ with an estimated IC50 value of 5.2 μM was found to be a potent inhibitor of Na,K‐ATPase activity, whereas Na,K‐ATPase was less sensitive to the pyrethroids tested and piperonyl butoxide. Investigation with circular dichroism (CD) spec‐troscopy showed that inhibition occurs through conformational changes of the α‐subunit of the enzyme. The kinetic characteristics of inhibition of Na,K‐ATPase with varying substrate (ATP) concentrations as well as with varying Na⁺ concentrations exhibited a competitive type of inhibition with Pb²⁺ in the μM range. With Pb²⁺ alone in the enzyme assay no conformational changes of the protein could be observed which confirmed the assumption that Pb²⁺ can bind to the Na⁺ binding site of the α‐subunit. Uncompetitive type of inhibition occurred with varied K⁺ concentrations demonstrating that this cation binding site is not affected directly by Pb²⁺.

Complete reversal of Pb²⁺ by DTT confirms that a possible target for interaction of this heavy metal ion with Na, K‐ATPase are specific SH groups.

Synergistic effects could only be determined with higher Pb²⁺ concentrations of 3, 5 and 7 μM plus piperonyl butoxide while all other combinations with this heavy metal plus organic substances where of the additive type. With CD spectroscopy also only additive effects were observed. These results demonstrate that higher concentrations of piperonyl butoxide favor the binding of Pb²⁺ to the Na⁺ binding site by conformational changes of the protein.     

Soil organic matter chemistry. Part 1. Characterization of several humic preparations by proton and carbon‐13 nuclear magnetic resonance spectroscopy

Both laboratory and commercial preparations of humic substances (HSs) such as fulvic acids and humic acids along with HC1‐HF preparation of Manitoba peat soil organic matter were characterized using Fourier Transformation (FT) proton (¹H) and carbon‐13 (¹³C) nuclear magnetic resonance (NMR) spectroscopy. All the samples were dissolved in a solution of 0.4 N NaOD in D₂O. In the case of ‘H‐NMR spectroscopy, all the investigated humic samples displayed resonance absorption peaks in the region of 1–4 ppm indicating the likely presence of aliphatic protons in the preparations. However, with the exception of one fulvic acid preparation (extracted from Manitoba Carrol clay‐loam soil with 0.5 N NaOH), ¹H‐NMR spectra of all other samples provided evidence for strong aromatic character. The aliphatic and aromatic characteristics of such samples of HSs were further confirmed with the aid of ¹³C‐NMR spectra.     

Impact of phosphorous on biochemical changes in Hordeum vulgare L. in mixed cropping with chickpea

Multiple cropping (i.e. intercropping or mixed cropping) plays an important role in agriculture because of the effective utilization of resources, significantly enhancing crop productivity compared with that of monocultured crops. The study was planed to assess the effect of various concentrations (00, 30, 60, 90 kg ha(-1)) of phosphorous on the biochemical composition of grains of Hordeum vulgare L. (NDB-1050) in mixed cropping system with Chickpea. Phosphorous is an essential ingredient for plants to convert atmospheric N (N2) into an ammonium (NH4) as a useable form. The available nitrogen content was found more in the year 2006 (131 kg ha(-1)) than year 2005 (105 kg ha(-1)). The results of available nitrogen content were showed that the mixed cropping system enhances N fixation process because phosphorous also influences nodule development through its basic functions in plants as an energy source. Reducing, non reducing and total sugar content of H. vulgare L. were influenced by changes in the phosphorous doses. Maximum protein (13.43%) was obtained at 60 kg P2O5 ha(-1) during the year 2006. Lysine, tryptophan and methionine content were found maximum in year 2006, respectively. Total mineral content of grains of plant (0.99 g 100g(-1)) was found maximum by the application of 60 kg P2O5 ha(-1). It is possible that there was an increase in the soil N made available by the leguminous chickpea species, and this could be another reason why there was an increase in Hordeum vulgare L. shoot mass per plant with intercropping with chickpea.     

Persistence of chlorpyriphos in okra (Abelmoschus Esculentus) fruits and soil

Persistence of cypermethrin and chlorpyriphos in okra and soil were studied following the application of pre-mix formulation of insecticides Action 505EC (chlorpyriphos 50%?+?cypermethrin 5%) at single (275?g a.i.?ha^?1) and double dose (550?g a.i.?ha^?1). The average initial deposits of chlorpyriphos in okra were observed to be 0.07 and 0.15?mg?kg^?1 in single and double dose, respectively, which dissipated to 92% after 10 days for both the dosages. Residues of soil under okra crop were found to be 0.15?mg?kg^?1 at the single and 0.36?mg?kg^?1 at the double doses. These residues persisted up to 3 days at single and 5 days at double dose. The half-life (t _1/2) periods of chlorpyriphos on okra and soil were observed to be 0.6 days and 1.9 days for single and double dose, respectively. Residues of chlorpyriphos reached below detectable level (BDL) of 0.01?mg?kg^?1 in okra fruits after 7 days at single dose and in 15 days in double dose. In soil, residues of chlopyriphos persisted up to 5 and 7 days in single and double dose, respectively. Following foliar applications of a insecticide formulation (Action 505EC, (chlorpyriphos 50%?+?cypermethrin 5%) on okra at @ 275 and 550?g active ingredient (a.i.)?ha^?1 resulting in active applications of chlorpyriphos at the rate of 250 and 500?g a.i.?ha^?1 the average initial deposits of chlorpyriphos in okra were observed to be 0.07 and 0.15?mg?kg^?1, respectively. These residue levels dissipated to 92% after 10 days at both the dosages. Residues of soil under the okra crop were found to be 15?mg?kg^?1 at the single and 36?mg?kg^?1 at the double dose. The residues persisted up to 3 days at the single and 5 days at the double dose. The half-life (t _1/2) periods of chlorpyriphos on okra were observed to be 0.6 days for application rates, and 1.9 days for soil. Okra fruits and soil samples collected on the 7th and 15th day after application did not show any chlorpyriphos residues above their determination limits of 0.01 and 0.005?mg?kg^?1, respectively.     

Aniline removal by Photocatalytic reaction of iron(iii) mediated with dissolved organic matter

When light (> 370 nm) was allowed to interact with an aqueous solution containing dissolved organic matter (DOM) and Fe(III), removal of aniline (AN) was observed. This was due to the photocatalytic reaction of Fe(III) mediated by DOM. Syringic acid (SYA) and humic acid (HA) were used as DOM in the present study. The ¹⁵N‐NMR spectrum of the product mixture from the light irradiation of the SYA/Fe(III) system demonstrated that AN was covalently bound to SYA. The kinetics of AN removal were, therefore, interpreted by assuming covalent binding between DOM and AN. The amounts of covalent binding sites and the apparent second‐order rate constants could be evaluated, and the amounts of covalent binding sites decreased with the increases of the concentration of DOM. This is attributed that the polymerization of DOM by the photo‐oxidation competed with the covalent binding between AN and DOM.     

Ground water pollution by pesticides at the watershed‐soil catena scale: Lindane at the lower Colorado river basin (Argentina)

The movement of Lindane from application points at the surface soil towards the underground water and further transport within this compartment at the watershed‐soil catena scale, was inspected by measurements of the pesticide concentration in soil water at a controlled experiment where it was applied at a usual label dose. The concentrations of Lindane in soil water and the upper phreatic level were also measured at successive dates in samples obtained from a net of phreatimeter probes distributed over the area (1,500 km²) of the lower Colorado River basin (Bs. Aires, Argentina). The location of cultivated‐irrigated areas within the watershed was inferred from NDVI (Normalized Difference Vegetation Index)‐1 km‐10 day AVHRR images obtained at successive dates during the irrigation season. Feasible paths of underground gravitational water flows were computed by means of a GIS‐simulation model on the basis of local terrain slopes and aspects. The pattern of Lindane distribution over the basin was explained on the basis of the distribution of diffuse sources, the patterns of percolation and groundwater flows and the thermodynamic characteristics of the pesticide.     

Investigation of the hemolytic effects of various organophosphoric acid triesters (OPEs) and their structure‐activity relationship

The hemolytic effects of various organophosphonc acid triesters (OPEs) were investigated and they showed strong hemolyic toxicity except triethyl phosphate and tris(chloroethyl)phosphate. 2‐Ethylhexyl diphenyl phosphate (EHDP) showed the strongest toxicity. By quantitative structure‐activity relationship (QSAR) study, one‐parameter regression equation to estimate hemolysis was not obtained. But, two‐parameter regression equations were obtained which were enought to estimate EC₅₀ and EC₂₀. The correlation coefficients with the two‐parameter regression equations were 0.939 for log(l/EC₅₀) and 0.946 for log(l/EC₂₀).     

Allelopathic effects of weeds extracts against seed germination of some plants

This study investigated the allelopathic effects of various weeds extracts on seed germination of 11 crop species. Most of the weed extracts tested had inhibitory effects on seed germination of common bean, tomato, pepper, squash, onion, barley, wheat, and corn at different application rates as compared with the 10% acetone control. Chickpea seed germination was inhibited by extracts of Solanum nigrum L., Chenopodium album L., and Matricaria chamomilla L. (10%, 20% and 22.5%, respectively) at the end of 21 day incubation period. However, Glycyrrhiza glabra L., Sorghum halepense (L.) Pers., and Reseda lutea L. extracts stimulated chickpea seed germination at the rates of 95%, 94%, and 93%, respectively, compared to control. It was concluded that some of the weed extracts tested in this study could be used as inhibitor while others could be used as stimulator for the crops.     

Enzymatic and cellular level effects of chromium∗

Exposure of Cr to four hepatic enzymes activities of tilapia, viz. acid‐ and alkaline phosphatases, catalase and glucose‐6‐phosphatase, was contrary to the results obtained for Cd and Ni. This is the only heavy metal investigated thus far that dramatically augmented glucose‐6‐phosphatase by approximately 83% at a concentration of 12 mg L^‐1 in vivo in lieu of the fact of an initial inhibition of approximately 45 % at a lower concentration of Cr; 6 mg L^‐1. In the case of acid phosphatase and catalase activities progressive increment was observed up to 50 and 217% respectively at a concentration of 12 mg L^‐1 Cr. On the other hand, in contrast to all the investigated enzymes interestingly alkaline phosphatase was inhibited continuously at all concentrations up to 46% at 12 mgL^‐1 Cr. In vitro experiments were contrary to the above mentioned results, whereby all hepatic enzymes were inhibited with major inhibition observed for acid phosphatase of approximately 60% from 5 mgL^‐1 Cr onwards in the system.

At cellular level, Cr exposure at a lethal dose of 12 mgL^‐1 demonstrated similar effects to that of Cd. In general, the glycogen and fat reserves were depleted while lysosomal activity is increased. As compared to the effects of Cd, the mitochondria did not indicate any prominent reflection in the formation of intramitochondrial bodies. Further, similar to Cd, the cell membrane as well as nucleus were not affected.     

In vitro degradation of the herbicide atrazine by soil and wood decay fungi controlled through Elisa technique

The interaction between atrazine, a triazine herbicide, and a series of decay fungi was characterized in terms of biodegradation of the herbicide and its influence on fungal growth. The following fungi were studied: thermophilic cellulolytic (Penicillium sp. 13) and noncellulolytic (Humicola lanuginosa sp. 5 and 12) strains isolated from self‐heated plant composts, mesophilic diphenol oxidase producing strain Mycelia sterilia INBI 2–26, white‐rot fungi Cerrena maxima, Coriolopsis fulvocinerea and Coriolus hirsutus. Competitive enzyme immunoassay was elaborated for detection of atrazine in cultural liquid. During agar plate cultivation the growth of Humicola sp. 5 was promoted by atrazine whereas the growth of Humicola sp. 12 and Penicillium sp. 13 was suppressed whereas M. sterilia INBI 2–26 was not affected by the herbicide. Neither atrazine‐accelerated nor atrazine‐depressed thermophilic strains decomposed atrazine during 21‐day cultivation according to ELISA data. In contrast, white‐rot fungi Coriolus hirsutus, Coriolopsis fuhocinerea and Cerrena maxima degraded nearly 50% of the herbicide in 5‐day submerged cultivation and 80–92% of the herbicide up to the 40th day. The soil strain M. sterilia INBI 2–26 decomposed 70% of atrazine in 17‐day cultivation. The degradation level depended of the time of atrazine introduction to the growing media. The relationships between the degree of atrazine decomposition and laccase and Mn‐peroxidase production were shown.     

Fish Responses to Experimental Fragmentation of Seagrass Habitat

Abstract: Understanding the consequences of habitat fragmentation has come mostly from comparisons of patchy and continuous habitats. Because fragmentation is a process, it is most accurately studied by actively fragmenting large patches into multiple smaller patches. We fragmented artificial seagrass habitats and evaluated the impacts of fragmentation on fish abundance and species richness over time (1 day, 1 week, 1 month). Fish assemblages were compared among 4 treatments: control (single, continuous 9‐m² patches); fragmented (single, continuous 9‐m² patches fragmented to 4 discrete 1‐m² patches); prefragmented/patchy (4 discrete 1‐m² patches with the same arrangement as fragmented); and disturbance control (fragmented then immediately restored to continuous 9‐m² patches). Patchy seagrass had lower species richness than actively fragmented seagrass (up to 39% fewer species after 1 week), but species richness in fragmented treatments was similar to controls. Total fish abundance did not vary among treatments and therefore was unaffected by fragmentation, patchiness, or disturbance caused during fragmentation. Patterns in species richness and abundance were consistent 1 day, 1 week, and 1 month after fragmentation. The expected decrease in fish abundance from reduced total seagrass area in fragmented and patchy seagrass appeared to be offset by greater fish density per unit area of seagrass. If fish prefer to live at edges, then the effects of seagrass habitat loss on fish abundance may have been offset by the increase (25%) in seagrass perimeter in fragmented and patchy treatments. Possibly there is some threshold of seagrass patch connectivity below which fish abundances cannot be maintained. The immediate responses of fish to experimental habitat fragmentation provided insights beyond those possible from comparisons of continuous and historically patchy habitat.