Development and Evaluation of a Laboratory-Based Technique for Screening Somaclonal Regenerants of Watercress (Rorippanasturtium-aquatium) for Resistance to Crook Root Disease (Spongospora subterranea f. sp. nasturtii)

A laboratory based method has been developed for infecting watercress with the crook root fungus ( Spongospora subterranea f.sp. nasturtii ). This utilised plastic trays of nutrient solution on which watercress shoots, supported by floats, were grown for a pre-inoculation period of 14 days before an inoculum consisting of 1 g of crook roots was added. Seven watercress someclones derived from plantlets regenerated from callus of a parental commercial control line (clone A) were tested onthree separate occasions. No variation within the parental control plants was seen but significant variation both between and within the individual somaclones over successive tests was observed. Two somaclones showed increased resistance to crook root disease compared with parental control plants.     

Studies on watercress chlorotic leaf spot virus and on the control of the fungus vector (Spongospora subterranea) with zinc

Watercress chlorotic leaf spot virus (WCLV) caused a yellow leaf spot disease of watercress at Pickering, Yorkshire. The virus was mechanically transmitted to and maintained in Chenopodium quinoa, C. amaranticolor and Petunia hybrida in which it caused systemic symptoms. It could not be mechanically transmitted, however, from infected C. quinoa to Chrysanthemum, Gynura aurantia, potato, tomato, watercress or nine other species of Cruciferae. WCLV could be partially-purified after extraction in weak (0.05–0.1 M) but not strong (0.5 M) phosphate or tris/HCl buffer after clarification with diethyl ether and acidification to pH 3.9–4.0. Preparations were non-infective if treated with 5% (vlv) ethanol or n-butanol or if stored at — 12°C for 1 day or heated for 10 min at 54°C. Preparations were non-infective after treatment with RNase or proteinase K but not after treatment with DNase. The virus was present in roots of diseased watercress plants which also contained the watercress crook root disease fungus Spongospora subterranea f. sp. nasturtii. Tests showed that WCLV was transmitted by S. subterranea zoospores and that it persisted in the resting spores of the fungus. The crook root disease was controlled by adding 0.3–0.5 μg Zn/ml to the inlet water supply to the crop. The water that had flowed through the crop contained 0.05–0.10 μg Zn/ml. Although this increased the zinc content of the watercress from 8–9 in untreated beds to 16–48 μg Zn/g in treated beds, this was below the tolerance recommended by the Food Standards Committee. A method is described of obtaining accurate dilutions of solutions of zinc sulphate (20% w/v ZnSO₄.H₂O) in the water supplying the crop using solutions of the red dye Ariavit Amaranth.     

Unusual snail species involved in the transmission of Fasciola hepatica in watercress beds in central France

Four freshwater pulmonate species (Lymnaea ovata, L. stagnalis, Physa acuta, Planorbis leucostoma) were living in several watercress beds known for their relationships with human cases of fasciolosis, whereas L. truncatula was never found. The aims of these studies were to determine the prevalence of natural infections with Fasciola hepatica in snails and to verify if these species might ensure the full larval development of this trematode (with cercarial shedding) when they were experimentally subjected to F. hepatica only, or to co-infections with an other trematode species. Investigations were so carried out in six snail populations living in watercress beds (including three for P. acuta) and in four others originating from three brooks or a pond (as controls). Snails naturally infected with F. hepatica were found in two watercress beds inhabited by L. ovata (prevalence of infection: 1.4%) and P. leucostoma (0.1%), respectively. The L. ovata from the watercress bed could be infected at a higher size than those from the control population and the prevalence of this infection was greater in the bed population. Similar findings were noted for L. stagnalis. Despite single or dual infections, the results obtained with the four populations of P. acuta were unsuccessful. In contrast, the co-infections of young P. leucostoma with Paramphistomum daubneyi and F. hepatica resulted in the shedding of some F. hepatica cercariae. According to the authors, the occurrence of fasciolosis in these watercress beds would be the consequence of frequent natural encounters between parasite and snails (L. ovata, L. stagnalis), or of co-infections with P. daubneyi and F. hepatica (P. leucostoma). In watercress beds only colonized by P. acuta, a lymnaeid species would have ensured the larval development of F. hepatica but it would have been eliminated by P. acuta, as this last species was known to be invasive and could colonize open drainage ditches on siliceous soil.     

Somaclonal variation in watercress for resistance to crook root disease

Summary Watercress (Rorippa nasturtium-aquaticum) shoots were regenerated from callus initiated from petioles on a range of media. The best coefficient of regeneration was obtained when callus was induced on a medium containing 0.25 mgl^-1 thidiazuron and 0.05 mgl{si-1} 2,4-D, followed by regeneration on 0.25 mgl^-1 thidiazuron. Plants were then screened for resistance to crook root disease of watercress in a laboratory screening test which revealed significant somaclonal variation between the controls and some of the somaclones.     

Preliminary studies on the composition of major ions of some fish ponds of Malacca in Malaysia

Summary This paper presents data on the ionic composition of tropical pond waters. The discussion is on the major cations calcium (6.58 p.p.m.) and sodium (3.79 p.p.m.) and the anions bicarbonate (20.24 p.p.m.) and sulphate (21.69 p.p.m.). Some ponds have extremely low alkalinity (10 to 27 p.p.m.) and most of the ponds have poor dissolved calcium content (2.5 to 9.9 p.p.m.). Their pHs lie between 6.71 to 7.70 except the control pond F₁ which has a pH of 5.21. The chemical data show differences in the ionic composition between the various ponds of different sizes. The differences can be due to the accumulated organic matter, types of fish stocked and the supplementary feeds used in the ponds.     

SOME OBSERVATIONS ON THE BACTERIAL CONTENT OF WATER IN WATERCRESS BEDS

SUMMARY: Samples of water flowing into watercress beds had higher bacterial contents during the summer months although this was less marked among samples from deep underground sources. Outlet samples showed higher contents than inlet samples and the bacterial content varied markedly with season, being highest in summer.
The presumptive coli-aerogenes contents at 30°, 37° and 44° also showed a similar seasonal variation among samples from the outlets but the marked inferiority of samples other than from bores was no longer apparent after the water had flowed through the beds. The dominant types were Bact. aerogenes type I, pectate liquefiers, Bact. coli type I, and Intermediate type I.
The importance of the pectate liquefiers was confirmed by plating on pectate gel and by their isolation from these plates and from MacConkey's broth.     

STUDIES ON GLOEOSPORIUM MUSARUM CKE. AND MASSEE CAUSING STORAGE ROTS OF JAMAICAN BANANAS

Experimental inoculations indicate that several factors may influence the extent to which anthracnose, caused by Gloeosporium musarum , develops on bananas following wound-infection. Severity of disease increases with increasing 'grade' of maturity, 'full' fruit being more seriously affected than 'thin' fruit. The evidence suggests that Gros Michel fruit is less susceptible to this form of rot than fruit of the Lacatan or Robusta varieties. The amount of Gloeosporium -rot on fruit imported into the United Kingdom undergoes marked seasonal variation, being greatest during autumn and winter.
The presence of perforated 'Polythene' bags during cold storage (55° F.) appears to favour slightly the development of disease. Bagging had no significant effect on rotting during the subsequent ripening period. After wound-inoculation, disease incidence and severity decreased appreciably with increasing periods of storage at tropical temperatures (76–87° F.). Such a decrease was evident even when the humidity at the surface of the fruit was maintained at a high level (92–100%).
In several shipping trials, a post-harvest fruit-dip treatment with nystatin (200–400 p.p.m.) effected 40–70% control of anthracnose.     

FURTHER OBSERVATIONS ON THE BACTERIAL CONTENT OF WATER IN WATERCRESS BEDS

SUMMARY: Observations on two watercress beds in Kent have confirmed previous findings (Jones & Baker, 1955) that even in comparatively well-protected beds the coli-aerogenes content of the water may be high in summer. They have also shown that in spite of circumstances which would lead one to expect pollution, as in the case of one bed, the coli-aerogenes content can be low in winter. The season appears to influence the content in the water of coli-aerogenes bacteria, pectate liquefying bacteria and those capable of growing at 37°, but in the case of those growing at 22° other factors can play a more important part, as higher counts were not uncommon in winter. Seasonal effects were less marked with inlet samples; they were less influenced by atmospheric temperature, and little extraneous contamination occurred. Numbers increased as the sampling point moved from inlet to outlet.     

The influence of light on the growth of watercress (<Emphasis Type="Italic">Nasturtium officinale</Emphasis> R. Br.)

In stream ecosystems, the growth of aquatic primary producers is affected by spatial and temporal variations in the riparian canopy, which can influence the availability of light resources. Aquatic plants can acclimate to low light environments by employing a suite of morphological or physiological mechanisms to increase light capture or photosynthetic efficiency. Some species may also use alternate types of propagules to colonize environments with heterogeneous light environments. In a greenhouse experiment we examined the morphological and physiological response of watercress (Nasturtium officinale R. Br.) to a gradient of increasing light levels, which ranged from 7% ambient light to full sunlight. We also determined if watercress seedlings and vegetative fragments differed in their growth response to increasing light levels. Total biomass and root biomass of seedlings and vegetative fragments decreased with decreasing light levels. The difference in plant biomass across treatments was due to morphological changes in total canopy area and leaf area, both of which increased with decreasing light levels. Seedlings and vegetative fragments did not differ in their response to light availability, but vegetative fragments had higher final biomass as a result of higher initial biomass. Physiological acclimation to low light levels appears to be of secondary importance for watercress as the concentrations of total chlorophyll, chlorophyll a, chlorophyll b, and chlorophyll a:b did not differ among light levels or between seedlings and vegetative fragments. Seedlings and vegetative fragments grown under high light levels had a greater percentage of carbon and a lower percentage of nitrogen than plants grown under low light conditions. The results of this study indicate that watercress displays considerable morphological plasticity and acclimates to low light conditions primarily by increasing leaf area and canopy surface area. There is no evidence that the type of watercress propagule (seedling vs. vegetative fragment) imparts any growth advantage in low light environments and watercress grown from either type of propagule showed no differences in their morphological or physiological responses to varying light regimes. Handling editor: S. M. Thomaz     

Kinetics of the reactivation of the Hill reaction in CO2-depleted chloroplasts by addition of bicarbonate in the absence and in the presence of herbicides

In isolated broken chloroplasts photosynthetic electron transport requires the presence of CO₂ and/or bicarbonate. This bicarbonate effect on electron flow was measured in a medium containing 100 m M sodium formate. In this medium a dark incubation time with bicarbonate is required for the reactivation of the Hill reaction. We have measured the kinetics of the reactivation of electron flow by varying the dark incubation of CO₂-depIeted pea ( Pisum sativum L., cv. Rondo) chloroplasts with bicarbonate. The half-time of this reactivation appears to be 25 s when 2 m M bicarbonate is added.
The dinitrophenol herbicide, i -dinoseb, is shown to be a competitive inhibitor of the bicarbonate dependent Hill reaction with an inhibitor constant (K_i) of 31 n M . In the presence of 100 n M i-dinoseb or 100 n M DCMU the half-time of the reactivation by 2 m M bicarbonate appears to increase to about 58 s. We provide an explanation for these phenomena by analyzing the bicarbonate-thylakoid interaction on the basis of a simple reaction scheme. The binding of bicarbonate to the thylakoids appears to be a second order reaction with pseudo-first order kinetics. According to our analysis, any inhibitor, which is competitive with respect to the bicarbonate stimulation of the Hill reaction, should increase the half-time of the reactivation of the Hill reaction.     

Public Health Investigation of Two Outbreaks of Shiga Toxin-Producing Escherichia coli O157 Associated with Consumption of Watercress

An increase in the number of cases of Shiga toxin-producing Escherichia coli (STEC) O157 phage type 2 (PT2) in England in September 2013 was epidemiologically linked to watercress consumption. Whole-genome sequencing (WGS) identified a phylogenetically related cluster of 22 cases (outbreak 1). The isolates comprising this cluster were not closely related to any other United Kingdom strain in the Public Health England WGS database, suggesting a possible imported source. A second outbreak of STEC O157 PT2 (outbreak 2) was identified epidemiologically following the detection of outbreak 1. Isolates associated with outbreak 2 were phylogenetically distinct from those in outbreak 1. Epidemiologically unrelated isolates on the same branch as the outbreak 2 cluster included those from human cases in England with domestically acquired infection and United Kingdom domestic cattle. Environmental sampling using PCR resulted in the isolation of STEC O157 PT2 from irrigation water at one implicated watercress farm, and WGS showed this isolate belonged to the same phylogenetic cluster as outbreak 2 isolates. Cattle were in close proximity to the watercress bed and were potentially the source of the second outbreak. Transfer of STEC from the field to the watercress bed may have occurred through wildlife entering the watercress farm or via runoff water. During this complex outbreak investigation, epidemiological studies, comprehensive testing of environmental samples, and the use of novel molecular methods proved invaluable in demonstrating that two simultaneous outbreaks of STEC O157 PT2 were both linked to the consumption of watercress but were associated with different sources of contamination.     

Cell shape and microtubules in zoospores of the green algaChlorosarcinopsis gelatinosa (Chlorosarcinales): Effects of low temperature

Summary The effect of low temperature (2 °C) on cell shape and microtubules in zoospores of the green algaChlorosarcinopsis gelatinosa has been investigated. The zoospores are 4–6 times longer than wide with a mean length of 12,5 m and can be kept in the dark for several hours without changes in cell shape. Cell shape changes have been evaluated quantitatively by measuring changes in cell length. Low temperature induces a decrease in cell length which exhibits a two-step kinetic: during the first 30 minutes a rapid rate of decrease in cell length was measured, while during the next 4 hours a slow rate of decrease in cell length was observed. Complete regeneration of zoospore length occurs when cold-treated cells are subjected to the original zoospore induction temperature (30 °C) for two hours. Observation of numbers, disposition and types of microtubules in the zoospore during decrease in cell length has shown that within 30 minutes after cold application the secondary cytoskeletal microtubules (scmt) disappear, while flagellar root microtubules are unaffected. During this period most cells develop a prominent posterior appendage (tail). Sections demonstrate the presence of several microtubules in these tails. Flagellar root microtubules probably extend into the tails and disappearance of scmt starts at the posterior pole of the cell. Regeneration of zoospores to original cell length is coupled with reappearance of scmt starting at the anterior pole of the cell. It is concluded that secondary cytoskeletal microtubules constitute the main cytoskeleton inChlorosarcinopsis zoospores and that flagellar root microtubules contribute to only a minor extent to the cytoskeleton, because they cannot retain the cell shape. The results are discussed with respect to the functional significance of flagellar root microtubules in green algae.     

Predation of incubator birds (Megapodius freycinet) by Komodo dragons (Varanus komodoensis)

A short study was made of the nesting habits of a species of megapode, Megapodius freycinet on the island of Komodo. The birds were found to build giant nesting mounds (0.95 × 7.15 m) in scrub and woodland close to the seashore or alongside river beds; 23 active and 19 abandoned mounds were located in an area of 250 ha.
The mounds were apparently added to from year to year, and consisted of dry sand and soil, plus leaves and sticks in most cases. The upper parts of the mounds were invariably exposed to the direct rays of the sun; the temperature within the active mounds was 33–37° C and slightly less in mounds not in use by the birds. According to the local people the nesting season of the megapodes extended from late August to November, and the chicks were hatched before the arrival of the rains in December. Up to four eggs had been recovered from a single mound.
The active mounds were all spaced apart by at least a 100 m, and the closest ones were usually separated by a river bed. This pattern suggested the species was territorial. One or two birds were often seen scraping at a mound or feeding close by, and their behaviour was recorded.
The Komodo dragon, Varanus komodoensis , was a frequent visitor to the nesting mounds of the megapodes, and was able to burrow into them and steal the eggs.     

Response to mowing of coastal brackish meadow plant communities along an elevational gradient

Over a six year period, 1979–1985, eight stands of till then ungrazed and unmown brackish meadow plant communities were treated by mowing once a year (August), in order to detect the response of the vegetation. The stands were distributed along a local elevation gradient, which was found to influence the composition of the vegetation through a complex-gradient, composed by unidirectional gradients in inundation, in ground water level and in Na as per cent of Ca+Mg+Na+K.
The mowing was carried out within 5 ×5 m treatment plots and the effect was indicated by quantitative analysis of the vegetation. A natural succession progressing at the locality, most distinctly manifested by expansion of Phragmites australis , was traced during the study period by means of unmown control plots.
The mowing caused increase in species diversity in all stands, mainly due to increase in evenness among the species.
The resistance of the stands to the mowing was found to differ in relation to elevation and to the initial composition of the vegetation. In upper geolittoral Festuca rubra stands the resistance was high and the mowing did not affect presence or colonisation of Phragmites . In upper-middle Festuca rubra stands resistance was lower, mainly indicated by suppression of Phragmites . Low elevation Scirpus maritimus reed beds on waterlogged soil was rather resistant, but four additional years of mowing led to a change into Agrostis stolonifera-Puccinellia maritima meadow. The resistance of low elevation Phragmites reed bed was low, as the mowing within a few years changed the reed bed into Agrostis stolonifera meadow.
The results were discussed in relation to the use of mowing as a nature conservation management tool in salt meadows.     

Effects of light and acetate on the liberation of zoospores by a mutant strain ofChlamydomonas reinhardtii

In light-dark-synchronized cultures of the unicellular green algaChlamydomonas reinhardtii, release of zoospores from the wall of the mother cell normally takes place during the second half of the dark period. The recently isolated mutant ls, however, needs light for the liberation of zoospores when grown photoautotrophically under a 12 h light-12 h dark regime. The light-induced release of zoospores was found to be prevented by addition of the photosystem-II inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Furthermore, light dependence of this process was shown to be abolished when the mutant ls was grown either photoautotrophically under a 14 h light-10 h dark regime or in the presence of acetate. Our findings indicate that the light-dependency of zoospore liberation observed in cultures of this particular mutant during photoautotrophic growth under a 12 h light-12 h dark regime might be attributed to an altered energy metabolism. The light-induced release of zoospores was found to be prevented by addition of cycloheximide or chloramphenicol, antibiotics which inhibit protein biosynthesis by cytoplasmic and organellar ribosomes, respectively. Actinomycin D, an inhibitor of RNA synthesis, however, did not affect the light-induced liberation of zoospores.Sporangia accumulate in stationary cultures of the mutant ls. Release of zoospores was observed when these sporangia were collected by centrifugation and incubated in the light after resuspension in fresh culture medium. Since liberation of zoospores was not observed after dilution of the stationary cultures with fresh culture medium, we suppose that components which interfere with the action of the sporangial autolysin are accumulated in the culture medium of the mutant ls.Abbreviation DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea     

PCR analysis of the presence and location of Mycobacterium avium in a constructed reed bed, with implications for avian tuberculosis control

The potential of reed beds to act as biofilters of pathogenic and environmental mycobacteria was investigated through examination of the fate of mycobacteria in a constructed reed bed filtering effluent from a large captive wildfowl collection. Particular emphasis was placed on the presence and location of Mycobacterium avium – the causal agent of avian tuberculosis (ATB) – in an effort to clarify the potential role of reed beds in the control of this disease. Water, sediment, and stems and roots of common reed ( Phragmites australis ) and greater reedmace ( Typha latifolia ) were taken from 15 locations within the reed bed plus sites upstream and downstream. Samples were analysed for mycobacteria using PCR and specifically for M. avium using nested PCR. Environmental mycobacteria were found throughout the entire reed bed but M. avium was not found downstream of the first vegetation growth. The reed bed was found to effectively remove M. avium from the water through a combination of sedimentation and adsorption onto vegetation stems. The results of this study show that constructed reed beds composed of a settlement lagoon and one or more vegetation beds can act as valuable and ecologically friendly tools in the environmental control of ATB.     

Inhibition of polar calcium movement and gravitropism in roots treated with auxin-transport inhibitors

Primary roots of maize (Zea mays L.) and pea (Pisum sativum L.) exhibit strong positive gravitropism. In both species, gravistimulation induces polar movement of calcium across the root tip from the upper side to the lower side. Roots of onion (Allium cepa L.) are not responsive to gravity and gravistimulation induces little or no polar movement of calcium across the root tip. Treatment of maize or pea roots with inhibitors of auxin transport (morphactin, naphthylphthalamic acid, 2,3,5-triiodobenzoic acid) prevents both gravitropism and gravity-induced polar movement of calcium across the root tip. The results indicate that calcium movement and auxin movement are closely linked in roots and that gravity-induced redistribution of calcium across the root cap may play an important role in the development of gravitropic curvature.Abbreviations 9-HFCA 9-hydroxyfluorenecarboxylic acid - NPA naphthylphthalamic acid - TIBA 2,3,5-triiodobenzoic acid - IAA indole-3-acetic acid     

Root hairiness: effect on fluid flow and oxygen transfer in hairy root cultures

The effect of root hairiness on fluid flow and oxygen transfer in hairy root cultures was investigated using wild-type, transgenic and root-hair mutants of Arabidopsis thaliana. The root hair morphologies of the A. thaliana lines were hairless, short hairs, moderately hairy (wild-type) and excessively hairy, and these morphologies were maintained after transformation of seedlings with Agrobacterium rhizogenes. Filtration experiments were used to determine the permeability of packed beds of roots; permeability declined significantly with increasing root hairiness as well as with increasing biomass density. Hairy roots of wild-type A. thaliana grew fastest with a doubling time of 6.9 days, but the hairless roots exhibited the highest specific oxygen uptake rate. In experiments using a gradientless packed bed reactor with medium recirculation, the liquid velocity required to eliminate external mass transfer boundary layer effects increased with increasing root hairiness, reflecting the greater tendency towards liquid stagnation near the surface of roots covered with hairs. External critical oxygen tensions also increased with increasing root hairiness, ranging from 50% air saturation for hairless roots to ca. 150% air saturation for roots with excessive root hairs. These results are consistent with root hairs providing a significant additional resistance to oxygen transfer to the roots, indicating that very hairy roots are more likely than hairless roots to become oxygen-limited in culture. This investigation demonstrates that root hairiness is an important biological parameter affecting the performance of root cultures and suggests that control over root hair formation, either by use of genetically modified plant lines or manipulation of culture conditions, is desirable in large-scale hairy root systems.     

THE ECOLOGY OF ANISOPUS FENESTRALIS SCOP. (DIPTERA) IN SEWAGE BACTERIA BEDS

The assessment of populations of Anisopus fenestrate (Scopoli, 1763) in sewage bacteria beds by the trapping of adults at the surface has been previously proved to be unsatisfactory. Methods were therefore developed for determining the numbers of egg masses, larvae and pupae as well as the total organic matter in a unit volume of bed. The relative larval populations of three areas under investigation were related to the loading of the beds as measured by the sewage strength and rate of application. In the upper 2 ft. 6 in. the numbers of larvae and pupae per unit volume of bed decreased with depth. There was no evidence of any vertical migration of the larvae before pupation. The horizontal distribution of larvae was found to be affected by the method of distribution. In beds served with fixed spray jets larvae are more abundant nearer the jets than at some distance away. In beds served with travelling distributors the larvae are more abundant in the zones below the jets than in the drier intermediate zones. In both cases relatively higher percentages of pupae in the drier zones might indicate a horizontal migration of larvae before pupating or of the pupae themselves.
The incidence of the larvae throughout 1949 in all three beds showed recurring peaks. In the following year a more intensive investigation on one area showed that this was due to successive generations of the fly; the proximity of the peaks is determined mostly by temperature and their size by the amount of food available in the bed during the larval grazing phase.
In the area not treated with insecticide intraspecific competition during a period when food was limiting, due to depletion by the previous generation, resulted in a natural reduction in the population. In the area treated with insecticide the food was retained and this natural control was thereby delayed.     

Effect of chronic lithium administration on endothelium-dependent relaxation of rat mesenteric bed: role of nitric oxide

The mechanism of action of lithium, an effective treatment for bipolar disease, is still unknown. In this study, the mesenteric vascular beds of control rats and rats that were chronically treated with lithium were prepared by the McGregor method, and the mesenteric vascular bed vasorelaxation responses were examined. NADPH-diaphorase histochemistry was used to determine the activity of NOS (nitric oxide synthase) in mesenteric vascular beds. We demonstrated that ACh-induced vasorelaxation increased in the mesenteric vascular bed of rats treated with lithium. Acute No-nitro-L-arginine methyl ester (L-NAME) administration in the medium blocked ACh-induced vasorelaxation in the control group more effectively than in lithium-treated rats, while the vasorelaxant response to sodium nitroprusside, a NO donor, was not different between lithium-treated and control groups. Acute aminoguanidine administration blocked ACh-induced vasorelaxation of lithium-treated rats, but had no effect in the control rats. Furthermore, NOS activity, determined by NADPH-diaphorase staining, was significantly greater in the mesenteric vascular beds from chronic lithium-treated rats than in those from control rats. These data suggest that the enhanced ACh-induced endothelium-derived vasorelaxation in rat mesenteric bed from chronic lithium-treated rats might be associated with increased NOS activity, likely via iNOS. Simultaneous acute L-NAME and indomethacin administration suggests the possible upregulation of EDHF (endothelium-derived hyperpolarizing factor) in lithium-treated rats.