A Possible Role for Urease as a Storage Protein in Aspergillus tamarii

A marked decrease in mycelial urease activity during the endogenousphase of undifferentiated Aspergillus tamariicultures was foundto be independent of preparative procedures but related to thedepletion of external nutrients. The enzyme, which was synthesizedduring the active growth stage, was produced in similar quantitieswith ammonium or urea as sole nitrogen source and at its peakrepresented c. 8·5 per cent of the total soluble proteinpool of the mycelium. It was found to show maximum activityat pH 8·20–8·65 when measured in cell-free,phosphate-buffered extracts. Isolation of urease from differentstages of the endogenous phase by affinity chromatography hasshown that the observed decrease in activity was due to breakdownof the enzyme protein in mature cultures, followed by the progressivedeactivation of residual enzyme during the autolytic stage.Since selective inhibition of 80–90 per cent of activityby acetohydroxamic acid in media containing urea as the onlynitrogen source or total repression of urease synthesis by L-histidinein ammonium-grown cultures did not interfere with normal growth,it was concluded that in A. tamarii urease fulfils the functionof a storage protein with a measure of catalytic activity. Aspergillus tamarii, urease, storage protein, nitrogen metabolism     

Immunization of mice with gamma-irradiated intramuscularly injected schistosomula of Schistosoma mansoni

The parameters involved in the induction of resistance against Schistosoma mansoni by injection of irradiated, artificially transformed schistosomula were studied in mice. Single intramuscular injections of 500 schistosomula exposed to radiation doses in the range 2.3 to 160 krad. resulted in significant protection (in the range 20 to 50% as assessed by reduced worm burdens) against a challenge infection administered at intervals from 3 to 24 weeks post-vaccination. However, schistosomula irradiated with 20 krad. consistently resulted in better protection than those exposed to either higher or lower radiation doses despite the persistence of stunted adults from the infections irradiated with 2.3 krad. Vaccination with 40 krad. schistosomula resulted in significant protection in terms of reduced worm and tissue egg burdens and increased survival following lethal challenge. Varying the number of irradiated schistosomula, the frequency and route of their administration, the site of challenge and the strain of host all failed to enhance the level of resistance. However, percutaneously applied, irradiated cercariae were found to be more effective in stimulating resistance (60%) than intramuscularly injected, irradiated schistosomula (40%).     

Effects of gamma radiation on spermatophore production and reception and subsequent fecundity and egg viability inAcarus siro L. (Acari: Acaridae)

Gamma radiation at doses higher than 10 krad significantly lowered the fecundity of the grain mite,Acarus siro. The fecundity of irradiated females was inversely correlated with dose, both when control or irradiated males were used in the pairing.Irradiation with ionizing radiation affected sexual activity of males. At doses above 10 krad the number of formed or observed spermatophores was lowered significantly.Sexual attractiveness of irradiated and control females to irradiated males was similar. However, non-irradiated males were observed mating more often with non-irradiated than with irradiated females.No correlation was found between the numbers of spermatophores present in the spermathecae of the female and the fecundity of the female. Irradiation had a greater effect on fecundity of the female than on sexual activity of the male; it did not affect the shape or behavior of spermatophores in the spermathecae of the female.Viability of eggs laid by females decreased by at least 50% when females or males were irradiated with doses above 20 krad. Irradiation also affected the survival of adults, but females were more sensitive than males. Net sterility index indicates that doses higher than 20 krad induce more than 90% sterility.     

Effect of irradiation on the protein profile,protein content,and quality of agar from <Emphasis Type="Italic">Gracilaria asiatica</Emphasis> Zhang et Xia (Rhodophyta)

There are about 15 species of Gracilaria reported in Vietnam. Of these, Gracilaria asiatica Zhang et Xia is being cultivated on a large scale in Northern Vietnam, which has a subtropical climate. During the rainy season, from May to October, the growth of G. asiatica is drastically reduced or even ceases due to very low salinity and high temperature. Therefore, it is important to improve the tolerance of G. asiatica to a wide range of salinity and temperatures. This paper presents the results of research on strain improvement of G. asiatica using irradiation and selection media. Three irradiation doses of 20, 60, and 100 krad were tested against the control (with no irradiation). Afterward, the seaweed biomass was cultivated on a selected medium, ESS-1, containing NaCl in concentrations of 23‰ (C1) and 0‰ (C2). The results showed that a higher survival rate of G. asiatica was observed with the 20- and 60-krad doses. The protein content and composition of selected seaweeds were analyzed and compared with the control. SDS-PAGE showed no remarkable difference in the protein composition between the control and irradiated samples. However, the 67-kDa protein band of seaweed treated with 20 and 60 krad, then grown on ESS-1 medium with 23% NaCl, had a higher density than other samples. This protein was reported to play an important role in G. asiatica, by enhancing its tolerance to variable salinity and temperature. Although the organic and inorganic content of all samples remained almost the same, the content and quality of agar extracted from irradiated seaweeds were higher than those of the controls. Due to the high amount of 3.6 anhydro-α-L-galactose combined with low amounts of sulfate found in irradiated seaweeds, the freezing and melting points of extracted agar were lower. Eventually, this resulted in higher condensation and better quality of agar, such as in its gel-forming ability. The quality of fluid agar extracted from selected seaweeds improved as shown in the remarkable decrease in Ca²⁺, Mg²⁺, and total Fe ion content, thus lowering its melting point compared with the control. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Inhibition of fibroblast proliferation in cardiac myocyte cultures by surface microtopography

Cardiac myocyte cultures usually require pharmacological intervention to prevent overproliferation of contaminating nonmyocytes. Our aim is to prevent excessive fibroblast cell proliferation without the use of cytostatins. We have produced a silicone surface with 10-µm vertical projections that we term "pegs," to which over 80% of rat neonatal cardiac fibroblasts attach within 48 h after plating. There was a 50% decrease in cell proliferation by 5 days of culture compared with flat membranes (P < 0.001) and a concomitant 60% decrease (P < 0.01) in cyclin D1 protein levels, suggesting a G₁/S₁ cell cycle arrest due to microtopography. Inhibition of Rho kinase with 5 or 20 µM Y-27632 reduced attachment of fibroblasts to the pegs by over 50% (P < 0.001), suggesting that this signaling pathway plays an important role in the process. Using mobile and immobile 10-µm polystyrene spheres, we show that reactive forces are important for inhibiting fibroblast cell proliferation, because mobile spheres failed to reduce cell proliferation. In primary myocyte cultures, pegs also inhibit fibroblast proliferation in the absence of cytostatins. The ratio of aminopropeptide of collagen protein from fibroblasts to myosin from myocytes was significantly reduced in cultures from pegged surfaces (P < 0.01), suggesting an increase in the proportion of myocytes on the pegged surfaces. Connexin43 protein expression was also increased, suggesting improved myocyte-myocyte interaction in the presence of pegs. We conclude that this microtextured culture system is useful for preventing proliferation of fibroblasts in myocyte cultures and may ultimately be useful for tissue engineering applications in vivo. tissue engineering; cell culture; cell cycle     

East coast fever: 60Co-irradiation of Theileria parva in its tick vector, Rhipicephalus appendiculatus

Three experiments were carried out in which Theileria parva was irradiated in its tick vector, Rhipicephalus appendiculatus. In the first experiment, infected unfed adult ticks were irradiated at doubling doses from 4 to 32 krad. Some of the ticks were then fed for 4, 5, 6, 7 and 8 days on rabbits, and the parasites in their salivary glands examined. Five male and 5 female ticks from each irradiation dose were put onto each of a pair of susceptible cattle, whose reactions were recorded. Increasing doses of irradiation resulted in progressive destruction of the parasites. All cattle receiving ticks irradiated at doses up to and including 16 krad died of East Coast fever (ECF), and one of the cattle receiving ticks irradiated at 32 krad died.In the second experiment, recently engorged nymphs were irradiated at 1, 2 or 4 krad, and moulting nymphs at doses of 2, 4, 8, 12, 16 or 32 krad. The salivary glands of the resultant adult ticks were examined after the ticks had fed for 4, 5, 6, 7 or 8 days on rabbits. Engorged nymphs irradiated at 4 krad failed to moult, whilst moulting nymphs irradiated at 32 krad moulted but failed to attach to rabbits. Doses of irradiation survived by the ticks had no apparent morphological effect on the parasites they contained.In the third experiment, infected unfed adult ticks were irradiated at 0, 5, 10, 15, 20 25 30, 35, 40, 45, 50 or 60 krad. The ticks were fed on rabbits for 5, 6 or 7 days. Some of them were then examined morphologically, whilst others were ground in MEM/BPA and aliquots of the supernatant used to inoculate groups of 5 cattle. The reaction of these cattle, together with the morphological examination of the parasites, suggested that increasing doses of irradiation destroyed increasing numbers of parasites.     

The effects of gamma-irradiation on migration and survival of Schistosoma mansoni schistosomula in mice

Infections with irradiated Schistosoma mansoni were established by intramuscular (i.m.) injection of mechanically transformed schistosomula. A dose of 2.3 krad. allowed persistence of a small proportion of worms to adulthood, and of these survivors the majority of the female worms were sexually sterile. However, a small proportion of 2.3 krad.-irradiated females and a larger proportion of similarly irradiated males were capable of pairing successfully with non-irradiated partners. Radiation in the range 2.3 to 10 krad. resulted in slightly reduced peak recoveries from the lungs while 20 krad. resulted in a much reduced and 40 krad. a virtual absence of survival to the lung stage. Increasing doses of radiation in the range 2.3 to 10 krad. resulted in successively fewer parasites reaching the liver. Thus, the major sites of the radiation-induced mortality appeared to be as follows: 2.3 krad., mainly in the liver; 4 krad., in the lungs and liver; 10 krad., mainly in the lungs; 20 krad., at the injection site and in the lungs and 40 krad., mainly at the injection site. The infections studied here showed reduced survival following exposure to high doses of radiation compared with the infections, established as percutaneously applied cercariae, which have been reported by other workers. Possible reasons for the disparity are discussed.     

Changes of adenine nucleotides content and release reaction of human blood platelets following gamma irradiation

The aim of this work was to examine the effect of gamma irradiation on the energy metabolism and physiological functions of blood platelets. Blood platelets were irradiated with a 60Co-source in the range of 0.5--8.0 krad. Before and after irradiation, the free nucleotide content of platelets and the ability of platelets to perform their hemostatic functions (the release reaction with thrombin) were determined. The obtained results demonstrated that: 1. ATP, ADP and AMP content reached minimum values at 1.5--2.0 krad. 2. The ability of platelets to perform the release reaction correlates with the ATP level at doses of 1.5--2.0 krad. At higher doses (6.0--8.0) disturbances of the release reaction, indicating damage to the platelet plasma membranes, were observed.     

Germination and Food Reserves in Bambarra Groundnut Seeds (Voandzeia subterranea Thouars) after Different Periods of Storage

Studies were made on bambarranut seeds (Voandzeia subterraneaThouars) after 0, 6, 12, 18 and 24 months of storage in gunnybags under laboratory conditions (25–35 °C). Seeddeterioration during storage was indicated by delayed germination,reduced germinability, reduced growth of seedlings and increasednumber of stunted seedlings culminating in a total failure ofgermination after two years. Slight depletion of food reserves occurred during seed storage.The loss in fat was higher than starch or protein. Total solublesugars decreased while the content of total fatty acids andamino acids and soluble protein increased. Total nitrogen (N)remained unaffected while soluble-N and amino-N increased. Allthese components showed a rapid change (increase or decrease)from 12 months to 18 months of storage which was associatedwith commencement of rapid decline in germinability of the seedsand growth of the seedlings. Initial rapid imbibition of water was observed in viable aswell as non-viable seeds, though at a higher rate in the latterand followed by a lag period in both. At the end of 24 h ofimbibition, water content in non-viable seeds was less thanthat in viable ones. Key words: Voandzeia subterranea, Seed germination, Seed storage     

Effects of Kinetin on Growth and Nucleic Acid Metabolism in Suspension Cultures of L. Cucumis melo

At 0.05 and 0.5 mg per 1 of kinetin growth of cucumber suspensioncultures were promoted and at a higher level (5.0 mg per 1)it was inhibited. Total nucleic acids and protein increasedduring the lag phase and declined during the phase of exponentialgrowth. The nucleotides increased before there was any appreciableincrease in the amount of supernatant ribonucleic acid. TheRNA, soluble protein and ribo-nuclease activity also rose duringthe early period of growth and subsequently fell. Higher amountsof nucleotides, RNA and soluble protein were present at growthpromoting kinetin concentrations, but these were in smalleramounts at supra-optimal kinetin levels. But the rate of declineduring the period of increase in dry weight was slower comparedto the rest. There was reduced activity of RNase, which alsofollowed RNA and soluble protein in the pattern of changes duringthe course of culture.     

Effects of gamma radiation on development, sterility, fecundity, and sex ratio of Dermanyssus gallinae (DeGeer) (Acari: Dermanyssidae)

Protonymphal Dermanyssus gallinae were irradiated with 0.50, 0.75, 1.0, 3.0, and 6.0 krad of gamma radiation and subsequently monitored regarding their developmental, feeding, and mating success. Also, sex ratios of adults treated as protonymphs were recorded as were sex ratios of embryos and F1 adults produced by these adults. Doses up to 1.0 krad did not prevent development of treated protonymphs to the adult stage or stop mating. Three krad reduced the number of treated protonymphs attaining adulthood and 6.0-krad treatment prevented all mites from developing to the adult stage. Egg (embryo) production was normal for mites treated with 0.50 krad, but significantly curtailed by doses of 0.75 krad and greater. Radiation doses used in this study did not appear to affect the normal variable sex ratios observed in untreated mites.     

Early Developments in RNA, Protein, and Sugar Levels during Cold Stress in Winter Rye (Secale cereale) Leaves

Changes in freezing tolerance of winter rye (Secale cerealeL. cv. Voima) were determined for leaf tissues during a 1-weekcold stress, which was performed by transferring the 7-d-oldseedlings from a greenhouse (25°C, long day) to 3°Cand short day conditions. The development of cold hardeningwas shown by using an ion leakage test and by determining theamounts of carbohydrates, soluble proteins and RNA. The firstevidence of the development of freezing resistance was foundafter 1 d at low temperature, i.e. an LT₅₀ value increased from-5 to -7°C. Plants cold treated for 7 d reached an LT₅₀value of -9°C. This increase in freezing tolerance was foundto be associated with the increased levels of soluble carbohydrates,total RNA and soluble proteins. These metabolic changes indicatethe association with adjustment of growth and cell metabolismto low temperatures at the beginning of cold acclimation ofwinter rye.Copyright 1994, 1999 Academic Press Secale cereale L., winter rye, cold stress, proteins, RNA, sugars     

East Coast Fever of Cattle: 60Co Irradiation of Infective Particles of Theileria parva

SYNOPSIS. Infective particles (IPs) of Theileria parva , the causative organism of East Coast Fever of cattle, were harvested from the tick vector, Rhipicephalus appendiculatus , using an in vitro feeding technic. In a ranging experiment, pairs of cattle were inoculated with aliquots of suspensions of IPs irradiated at doses of 4–137.6 krad. Doses of irradiation in excess of 8 krad appeared to destroy the parasite. In the 2nd and 3rd experiments, groups of 5 cattle were inoculated with aliquots of suspensions containing low and high concentrations of IPs respectively, irradiated at doses of 4–32 krad. In the 2nd experiment, doses of irradiation in excess of 10 krad appeared to destroy the parasite. In the 3rd experiment, at least 1 animal became infected when inoculated with an aliquot of a suspension irradiated at 16 krad. In all experiments, it appeared that increasing doses of irradiation destroyed increasing numbers of IPs. There was no conclusive evidence that IPs which survived irradiation were attenuated, and it appears that vaccination of cattle against ECF is unlikely to be achieved by inoculation of irradiated IPs using the methods described.     

Physiological effects of glycinebetaine on gamma-irradiated stressed fenugreek plants

Irradiation stress adversely affects plant growth and development. The radio protective activity by glycinebetaine in plants has not been reported, and its mechanism has not been known. Gamma rays at doses 0.0, 25, 50, 100, and 150 Gray (Gy) when applied pre-sowingly to dry seeds of fenugreek from a cobalt source (⁶⁰Co) with strength of 500 Ci and the dose rate of 0.54 Gy/min significantly reduced chlorophyll content, total protein, photosynthetic efficiency (¹⁴CO₂-fixation), total dry weight, the accumulation of reducing, non-reducing and total soluble sugars in comparison with un-irradiated control. It also significantly repressed the activities of hydrolytic enzymes (α-amylase and invertase), the carboxylating enzyme (ribulose-1,5-bisphosphate-carboxylase/oxygenase) in the developed fenugreek plants. Soaking irradiated seeds with glycinebetaine (50 mM) for 24 h partially alleviated the depression effects of irradiation in these parameters. γ-irradiation treatment increased significantly H₂O₂ content. Presoaking irradiated seeds with GB decreased significantly the H₂O₂ level. The magnitude of the reversal decreased with increasing the irradiation dose. γ-irradiation induced a significant decrease in the level of nucleic acids (DNA and RNA) accompanied by a corresponding induction of hydrolytic activities of DNase and RNase in the developed plants in comparison with un-irradiated control. Those changes were more significant at higher γ-ray doses. Post-treatment of irradiated seeds with GB partially alleviated the adverse effects of radiation. It significantly increased nucleic acid levels and repressed the activities of DNase and RNase. The protective role played by glycinebetaine was more significant at lower γ-ray doses. Pretreatment of seeds with GB may play an effective role in the radio-repair mechanism.     

Influence of Gamma Radiation on the Transport of Indolyl-3-Acetic Acid in Bark Tissue from Apple Trees

The influence of gamma radiation on the polarity of IAA translocation was investigated. Pieces of apple tree shoots, taken from 3-year-old trees, were irradiated in a dark irradiation chamber BK-⁶⁰Co source, 10 kCi. Doses from 20 to 150 krad were given. Strips of bark were peeled off both irradiated and control shoots. The middle parts of the bark strips were placed on agar blocks loaded with IAA-1-¹⁴C. The radioactivity of basal and acropetal segments was determined after about 20 h and results expressed as polarity quotient. It has been shown that irradiation with 20 krad (200 Gy) decreases the polarity quotient remarkably (polarity quotient of control equals 7; for 20 krad—2.9; 100 krad—1.6). The decrease in polarity results from inhibition of the basipetal translocation of IAA. Irradiated tissue shows a decrease in IAA uptake. Possible mechanisms of gamma irradiation effects on polar translocation of IAA are discussed.     

The influence of60Co γ-irradiation of pea seeds on the thiamine biosýnthesis in 10-daý plants

Pea seeds were subjected to 1; 5 and 20 krad doses of⁶⁰Co γ-raýs. The irradiated seeds were planted in damp sand and in Petri vessels. After 10-daý vegetation at room temperature and under natural light conditions the content of the following components was determined in ýoung plants: free thiamine and thiamine pýrophosphate and drý substance. It was found that 1 krad dose stimulates the growth of the plant and increases the crop of its green parts. The doses within the range of 1–5 krads do not affect the production of thiamine. The content of the latter, particularlý in its free form, increases markedlý for the dose of 20 krads. However, such doses hamper the vegetation. In conclusion it seems that doses of the order of 1 krad lead to positive results in respect to the growth of the plants, however, neither thiamine biosýnthesis nor its phosphorýlation is stimulated under these conditions.     

Types of Rot, Rate of Rotting, and Analysis of Pectic Substances in Apples Rotted by Fungi

The rate at which the fungi grew through apples was determinedin various ways and used to estimate their rate of linear advance.Five fungi were studied;they were Sclerotinia fructigena (firm-browncoloured rot, rapid growth through apples), Botrytis cinerea(soft, light-brown coloured rot, rapid growth through apples),Psyrenochaeta furfuracea (firm to soft rot, variable in colourbut generaly dark, slow growth through apples), Penicilliumexpansion A (soft, white rot, slow growth through apples) andPenicillium expansum B (soft, white rot, medium rate of growththrough apples). S. fructigena which had the highest rate oflinear advance which was about three times that of P. furfuraceawhich had the lowest. Methods for extracting different types of pectic substancesfrom sound and rotted tissues are described, and details aregiven of a rapid and reasonably accurate colorimetric methodof determining the anhydrogalacturonic acid content of theseextracts. The firm-rot fungi reduced the water-insoluble pecticsubstances by 10–20 per cent., but the soft-rot fungicaused much larger changes, up to 70 per cent. being degraded,The firm-rot and soft-rot fungi had different effects on thepectic substances insoluble in dilute acid but soluble in dilutealkali. The soft-rot fungi had little effect on these substances,or reduced their concentration, whereas the firm-rot fungi causedsubstantial increases compared with sound tissue. These resultsare considered in terms of pectic enzyme activity. Analysisof extracts by paper chromatography showed that galacturonicacid, absent from sound tissue, was present in each type ofrotted tissue. Di- and tri-galacturonic acids were present inrots caused by P. expansum, and these rots probably also containedproducts from the break-down of other polysaccharides.     

Mass rearing history negatively affects mating success of male Anastrepha ludens (Diptera: Tephritidae) reared for sterile insect technique programs

Mating competitiveness and sterility induction into cohorts of wild Anastrepha ludens (Loew) (Diptera: Tephritidae) was compared among wild and laboratory flies reared for use in the sterile insect technique Mexican program. Laboratory flies stemming from an 11-yr-old bisexual strain were either not irradiated, irradiated at 3 krad (low dose), or irradiated at 8 krad. In 30 by 30 by 30-cm Plexiglas cages, where a cohort of laboratory flies (male and female) irradiated at different doses (0, 3, and 8 krad) was introduced with a cohort of wild flies, males and females of each type mated randomly among themselves. Compared with nonirradiated laboratory and wild males, irradiated males, irrespective of dose (3 or 8 krad), induced shorter refractory periods and greater mating frequency in wild females. Nevertheless, laboratory flies irradiated at a low dose induced greater sterility into cohorts of wild flies than laboratory flies irradiated at a high dose. In a 3 by 3 by 3-m walk-in cage, wild males gained significantly more matings with wild females than nonirradiated and irradiated laboratory males a finding that revealed a strong effect of strain on mating performance. Mating incompatibility of the laboratory strain might have obscured the effect of reduced irradiation doses on male mating performance in the walk-in cage. Our results highlight an urgent need to replace the A. ludens strain currently used by the Mexican fruit fly eradication campaign and at least suggest that reducing irradiation doses result in an increase in sterility induction in wild populations.     

Inhibition of Somatic Embryogenesis in Tissue 2Medicago sativa by Aminoethoxyvinylglycine, Amino-oxyacetic acid, 2, 4-Dinitrophenol and Salicylic Acid at Concentrations which do not Inhibit Ethylene Biosynthesis and Growth

Meijer, E. G. M. and Brown, D. C. W. 1988. Inhibition of somaticembryogenesis in tissue cultures of Medicago sativa by aminoethoxyvinylglycine,amino-oxyacetic acid, 2, 4-dinitrophenol and salicylic acidat concentrations which do not inhibit ethylene biosynthesisand growth. J. exp. Bot. 39: 263–270. The effects of aminoethoxyvinyglycine (AVG), amino-oxyaceticacid (AOA), 2, 4-dinitrophenol (DNP) and salicylic acid (SA)on ethylene production, tissue proliferation and somatic embryo-genesisin a recently developed rapid in vitro regeneration system ofMedicago sativa L. were examined. Contrary to numerous publications,AVG, AOA and DNP did not affect the rate of ethylene biosynthesis,while SA even caused an increase in ethylene production. Allfour compounds were, however, potent inhibitors of somatic embryoformation in the M. sativa tissue cultures, even at concentrationswhich did not affect tissue growth. Generally, a 5-d exposureto the inhibitors reduced the number and quality of somaticembryos obtained. It is suggested that the inhibitors may notreach the site of action of enzymes involved in ethylene biosynthesisand may possibly block other biosynthetic pathways which areof crucial importance to somatic embryo development. The resultsindicate that a delicate differentiation process like somaticembryogenesis is very sensitive to metabolic perturbances. Theresults are also discussed in the light of other known effectsof these four compounds on higher plants. Key words: Ethylene, Medicago sativa, somatic embryogenesis, tissue culture     

Effect of low doses of ionizing radiation on cells cultured from the hematopoietic tissue of the Dublin Bay prawn, Nephrops norvegicus

Explant cultures from the hematopoietic tissue of the Dublin Bay prawn, Nephrops norvegicus, were exposed to low doses of (60)Co gamma radiation. Cells growing from the explants were examined 7 days after irradiation using light and transmission electron microscopy and were also tested for their ability to produce signals indicative of a bystander effect. The exposed cultures displayed pronounced damage and were orders of magnitude more sensitive than the data in the literature would suggest for arthropod cells. The cultures were also more sensitive than mammalian cells that were exposed to similar doses. Cellular abnormalities included damage to cytoplasmic organelles, particularly the cytoskeleton. Abnormal mitochondria were also prominent. At low doses (0.5 Gy), nuclear damage was not apparent in the cultures, but there was evidence of a dose-dependent increase in apoptosis. The irradiated cultures released a factor into the medium that was capable of inducing apoptosis and cell death in unirradiated fish and human cells. This bystander effect was of a similar magnitude to that reported for mammalian cell systems. It is suggested that these crustaceans may be highly sensitive to radiation, unlike terrestrial arthropods and certain other invertebrates, which are generally considered to be radioresistant.