Immature Segments Research Articles

Identification and expression analysis of a new small ubiquitin-like modifier from Taenia pisiformis

The small ubiquitin-like modifier (SUMO) plays important roles, with the SUMOylation pathway as one of its core components. In the present work, a single SUMO gene was initially identified from Taenia pisiformis and designated as TpSUMO. Bioinformatic analysis showed that the TpSUMO gene contained a 309 bp open reading frame (ORF), encoding 102 amino acids, and had a predicted molecular weight of ∼12 kDa. The amino acid sequence of TpSUMO was deduced and it shared 44.00% identity with human SUMO2 (HsSUMO2) and exhibited more than 97.78% identity with SUMOs from Taenia and Echinococcus. TpSUMO possessed a putative non-consensus site (FK11MG) within its N-terminus and a typical di-glycine (GG) motif at the C-terminus. Basic local alignment search tool (BLAST) analysis showed that only a single SUMO-related ortholog was present in each set of known genome data for fourteen tapeworm species. The precursor His-TpSUMO-FL, mature His-TpSUMO-GG and mutant His-TpSUMO-GGK11R proteins (∼18 kDa) were expressed in Escherichia coli Rosseta (DE3), and rabbit polyclonal anti-TpSUMO was generated with a high titer of 1.28 × 105. In vitro SUMOylation assay results showed that TpSUMO multimer formation in the His-TpSUMO-GG reaction could be catalyzed by the human SAE1/SAE2 and UBC9 conjugation system, but K11R mutation disrupted TpSUMO chain synthesis. Quantitative real-time PCR (qRT-PCR) further revealed that TpSUMO was ubiquitously expressed in different stages of T. pisiformis and in higher levels during an early development phase (day 14) of adult worms. Immunofluorescence localization showed that TpSUMO was detected in the bladder wall of cysticerci, in the testis in immature segment, and within eggs in the gravid proglottids. These findings indicated that TpSUMO is a new member of the SUMO protein family and may play a vital role in regulation of functions within proteins involved in worm growth and development.

First documentation of canine dipylidiasis by molecular detection in Baghdad City, Iraq

Canine dipylidiasis is a zoonotic intestinal cestode infects cands, fields and rarely human. The goal of this study was to determine morphological characteristics by traditional parasitological methods and molecular techniques among stray dogs in Baghdad, Iraq. Totally, thirty-two adults of D.caninum were isolated from 15 small intestines that were naturally infected obtained from 100 necropsied stray dogs (15%) and used for morphological description after using Semichon-acetocarmine stain, on the basis of morphological description of the scolex, immature, mature, and gravid segments of D.caninum The results revealed a significant difference (p> 0.01) in the dipylidiasis infection based on the dogs' sex, females had a higher infection rate (28%) than males (10.7%). In between aged groups, infection rates showed a relatively significant difference (P≤0.01) with a higher rate in puppies (20%) than in adults (13.8%). The records of D.caninum increased in March compared to the other months, with nil infection in August. By using the DC28SrRNA region at size (653bp) se, Polymerase Chain Reaction (PCR), DNA sequencing, and phylogeny were used for identification and genetic variation between thirty-two local D.caninum and NCBI.

CARBOHYDRATE PROFILE IN RELATION TO GROWTH AND DIFFERENTIATION OF PROGLOTTIDS OF CYCLOPHYLLIDEAN CESTODE, Raillietina tetragona (MOLIN, 1858) INFECTING DOMESTIC CHICK, Gallus gallus

Cestodes are endoparasites and exhibit a great degree of difference in morphology and physiology within the same body. Raillietina tetragona infects domestic chick, Gallus gallus. The present study investigated the transition in carbohydrate metabolites in relation to the differentiation of proglottids of Raillietina tetragona, infecting domestic chick. The glycogen content was estimated by Carroll et al (1956). It was 37.81±2.79, 44.71±1.78 and 34.05±4.02 mg glucose/g fresh weight of tissue in immature, mature and gravid regions; total carbohydrates in immature, mature and gravid regions were 23±3.94, 41.32±5.05 and 34.53± 3.58 mg glucose/g fresh weight respectively where as pyruvate levels were 4.78 ±0.40, 4.86 ±0.50 and 4.60±0.20 µg of pyruvate /gm fresh weight of parasite in immature, mature and gravid proglottids respectively. The data obtained from adult worm revealed that higher levels of activities were associated with mature and immature segments whereas the gravid segment was having low levels of all these metabolites. They respire by anaerobic and semi-aerobic modes that yield lesser amount of energy, and therefore they store higher levels of glycogen.

Molecular Characterization of Annexin B2, B3 and B12 in Taenia multiceps.

Coenurus cerebralis, the metacestode of Taenia multiceps, causes coenurosis, a disease severely affecting goat, sheep, cattle and yak farming and resulting in huge economic losses annually. Annexins bind calcium ions and play an important role in flatworm parasite development. To explore potential functions of annexins in T. multiceps, three homologous genes, namely, TmAnxB2, TmAnxB3 and TmAnxB12, were screened from the transcriptome dataset, amplified from C. cerebralis cDNA and subjected to bioinformatics analysis. Then, polyclonal antibodies recognizing the recombinant TmAnxB2 (rTmAnxB2) and rTmAnxB3 were prepared for localization of TmAnxB2 and TmAnxB3 in different tissues and developmental stages by immunofluorescence. The transcription of all three genes was also measured by relative fluorescent quantitative PCR. The sizes of rTmAnxB2, rTmAnxB3 and rTmAnxB12 were 58.00, 53.06 and 53.51 kDa, respectively, and rTmAnxB12 was unstable. Both rTmAnxB2 and rTmAnxB3 were recognized by goat-positive T. multiceps sera in Western blots. Immunofluorescence revealed that TmAnxB2 and TmAnxB3 were localized in the protoscolex and cyst wall and TmAnxB3 was also detected in adult cortex. TmAnxB2 and TmAnxB12 mRNA levels were determined to be highest in oncospheres and protoscolex, whereas transcription of TmAnxB3 was highest in scolex and immature segments. Taken together, these findings indicate that TmAnxB2 and TmAnxB12 may play critical roles in T. multiceps larvae, while TmAnxB3 may have important functions in adults. These results will lay the foundation for functional research of annexins in T. multiceps.

Hymenolepis diminuta: Experimental studies on the antioxidant system with short and long term infection periods in the rats

Many helminths cause long-lasting infections, living for several years in mammalian hosts reflecting a well balanced coexistence between host and parasite. There are many possible explanations as to how they can survive for lengthy periods. One possibility is their antioxidant systems, which can serve as defence mechanisms against host-generated oxygen radicals. Therefore, the aim of this experimental study was to examine the antioxidant system in Hymenolepisdiminuta during short (1.5months young tapeworms) and long (1.5years old tapeworms) term infection in the rat small intestine.The strobilae of H. diminuta tapeworms (14 young and three old) were divided into three pieces: the anterior part, containing the genital primordiae in the immature segments; the medial part, containing the early uterus in the mature, hermaphroditic proglottids and the terminal part with the mature gravid uterus in the gravid segments. Supernatants of these fragments were used for determination of markers of oxidative stress: concentration of thiobarbiturate reactive substances (TBARS) and of reduced glutathione (GSH), and the activity of antioxidant enzymes: superoxide dismutase (SOD1 and SOD2), catalase (CAT), glutathione peroxidases (GSHPxs), glutathione transferase (GST) and glutathione reductase (GSHR).The results indicated changes in levels of oxidative stress markers and antioxidant enzyme activity in both the young and old forms of H. diminuta. Relatively high activity of SOD (particularly in the anterior part of young tapeworms) was observed, as was increased activity of total GSHPx and a relatively high concentration of GSH in all parts of the tapeworms. These are caused by exposure to increased amount of ROS, which are produced during the inflammatory state. Due to the high activity of antioxidant enzymes, the anterior section of young and old tapeworms is equipped with a very effective antioxidant system. Old organisms also effectively resist oxidative stress due to reduced levels of lipid peroxidation and the high activity of GST, all of which suggest good adaptation to the hostile environment in the host’s intestine.

New Species in the Genus Monoecocestus (Cestoda: Anoplocephalidae) From Neotropical Rodents (Caviidae and Sigmodontinae)

Anoplocephalid cestodes have a worldwide distribution, but relatively few species are known from South American rodents. By examining the collections of the Harold W. Manter Laboratory of Parasitology and the United States National Parasite Collection, 6 new species of Monoecocestus Beddard, 1914, are described, along with a redescription of Monoecocestus mackiewiczi Schmidt and Martin, 1978, based on the type specimens. The discussion includes commentary about uterine development, an important taxonomic character of the family, the vaginal dilation in immature segments (a character of potential taxonomic importance), and the implication of host usage to the evolutionary history and biogeography of species in this genus.

The influence of torsion on disc herniation when combined with flexion

The role of torsion in the mechanical derangement of intervertebral discs remains largely undefined. The current study sought to investigate if torsion, when applied in combination with flexion, affects the internal failure mechanics of the disc wall when exposed to high nuclear pressure. Thirty ovine lumbar motion segments were each positioned in 2 degrees axial rotation plus 7 degrees flexion. Whilst maintained in this posture, the nucleus of each segment was gradually injected with a viscous radio-opaque gel, via an injection screw placed longitudinally within the inferior vertebra, until failure occurred. Segments were then inspected using micro-CT and optical microscopy in tandem. Five motion segments failed to pressurize correctly. Of the remaining 25 successfully tested motion segments, 17 suffered vertebral endplate rupture and 8 suffered disc failure. Disc failure occurred in mature motion segments significantly more often than immature segments. The most common mode of disc failure was a central posterior radial tear involving a systematic annulus-endplate-annulus failure pattern. The endplate portion of these radial tears often propagated contralateral to the direction of applied axial rotation, and, at the lateral margin, only those fibres inclined in the direction of the applied torque were affected. Apart from the 2 degrees of applied axial rotation, the methods employed in this study replicated those used in a previously published study. Consequently, the different outcome obtained in this study can be directly attributed to the applied axial rotation. These inter-study differences show that when combined with flexion, torsion markedly reduces the nuclear pressure required to form clinically relevant radial tears that involve cartilaginous endplate failure. Conversely, torsion appears to increase the disc wall's resistance to radial tears that do not involve cartilaginous endplate failure, effectively halving the disc wall's overall risk of rupture.

Factors influencing somatic embryogenesis and regeneration ability in somatic tissue culture of spring and winter rye

Rye is an important crop in Northern and Eastern Europe. However, the application of various biotechnologies in rye breeding has been limited duo to its recalcitrant in tissue culture. In order to improve somatic tissue effi ciency, key factors affecting somatic embryogenesis and reproducible green plant regeneration of rye (Secale cereale L.) were evaluated and optimised. In this study, a total 27 rye genotypes including 10 spring and 17 winter genotypes were involved in the investigation. Genotype, culture medium, sugar, gel agent and auxin infl uenced somatic embryogenesis of immature embryo signifi cantly. One-two weeks cold pretreatment of young embryo enhanced somatic embryogenesis and green plant regeneration. In culture of immature embryos, infl orescences and leaf segments of the seedlings, explants signifi cantly infl uenced the culture effi ciency. Highest embryogenic callus yield resulted from rye immature embryo as explant compared to young infl orescence and leaf segment of seedling. Developmental stage of embryo played an important role in somatic embryogenesis. Late spherical coleoptile stage (embryo size 0.5–1mm in length) was optimal developmental stage of immature embryo for culture. Morphogenetic potential of embryogenic callus decreased with an increasing number of subcultures, and this ability could be maintained in vitro for a maximum of 8 months of culturing.;

Changes in physicochemical properties and morphology of canna starches during rhizomal development

Canna rhizomes aged seven months were harvested, and their segments were classified into four groups: mother, immature, premature and mature segments, according to the sequence of development. Based on weight of the segments, the mature segment was the greatest part (70%), whereas the immature and premature were of comparable amounts (14% and 15%, respectively). The average weight of one rhizome was 5324 g. Starch content increased from the immature segment (13.7%) to the premature segment (19.5%), and slightly decreased in the mature segment (18.6%), while the mother segment had the lowest starch content (7.9%). The size of the starch granules increased with progressive development of segments from immature to premature and mature stages. Starch from the mother segment contained a higher proportion of small size granules than the other segments and unusual features were observed on the surface of some granules. The appearance of granules from the different samples subjected to the same period of hydrolysis by porcine pancreatic α-amylase was similar, although differences in the degree of hydrolysis were found. Signs of degradation were more readily seen as the period of hydrolysis was extended. The mode of attack by α-amylase on canna starch was principally digestion through surface corrosion. Starches from different segments showed similar crystalline structures, and thermal and pasting properties; however, some aspects of the chemical composition of starch from the mother segment were different from the others.

Production of cotyledon-type somatic embryos directly from immature cotyledonary explants of Camellia sinensis (L.)

SummaryAttempts were made to produce cotyledon-type somatic embryos from immature cotyledonary explants of Camellia sinensis (tea). Seeds of the tea cultivar ‘TRI 2043’ were collected at successive developmental stages, and separated into groups depending on the morphological complexity of the seed coat. Further separation was based mainly on the size (diameter) of the cotyledons in each seed (early, mid and late immature: stages 1–3; intermediate: stage 4; mature: stage 5). To determine the most suitable stage for direct somatic embryogenesis, sterilised cotyledons at various developmental stages were placed on MS basal medium containing 2 mg l–1 6-benzyl aminopurine (BAP) and 0.2 mg l–1 naphthalene acetic acid (NAA). The results indicated that immature cotyledons, 10 mm in diameter (stage 3), were most responsive for the production of typical (cotyledon-type) somatic embryos. Cytological examination revealed that typical somatic embryos exhibited gradual tissue differentiation. Immature (stage 3) cotyledon segments were placed on different media containing 0 – 3 mg l–1 NAA, in combination with 2 mg l–1 BAP, to select a suitable NAA concentration for efficient production of typical somatic embryos. The optimum concentration of NAA was in the range 0.2 – 1 mg l–1. Cotyledon-type and seed-like somatic embryos were developed in 0.2 and 1 mg l–1 NAA, respectively.

GALAXITAENIA TOLOI N. GEN., N. SP. (EUCESTODA: PSEUDOPHYLLIDEA) FROM GALAXIAS PLATEI (PISCES: OSMERIFORMES, GALAXIIDAE), IN THE PATAGONIAN REGION OF ARGENTINA

Galaxitaenia n. gen. (Eucestoda: Pseudophyllidea) is proposed to accommodate Galaxitaenia toloi n. gen., n. sp. from Galaxias platei, a freshwater fish inhabiting Andean lakes in Argentine Patagonia. Galaxitaenia belongs to the Triaenophoridae because it possesses a marginal genital pore, a ventral uterine pore, and a follicular vitelline gland. The new genus can be distinguished from other triaenophorids by the following combination of characters: a scolex with a prominent rectangular apical disc without hooks, grooves, or indentations; neck present; segments wider than long to quadrangular; testes in 2 lateral fields, often connected anteriorly; cirrus unarmed; an ovary situated posteriorly; a vagina posterior to the cirrus sac; vitelline follicles medullary, in 2 ventral fields forming 2 wings interrupted medially; a uterus saccate to branched; and eggs without operculum. The types, distribution, and density of microtriches were analyzed on the surface of the tegument of scolex, neck, and immature segments. The presence of tumuli were observed on the apical disc of the scolex. Galaxitaenia toloi n. sp. is the first triaenophorid species recorded in a South American freshwater fish and the fourth helminth parasitizing the intestine of G. platei.

Light-dependent developmental control of rbcS gene expression in epidermal cells of maize leaves.

Regulatory elements of the maize rbcS-m3 gene (a member of the family of genes encoding the small subunit of ribulose bisphosphate carboxylase) that are sufficient for expression of the beta-glucuronidase (gusA) gene in photosynthetic tissue lead to relatively weak expression of the reporter gene in epidermal cells of green maize leaves when delivered by ballistic gene transfer methods. However, epidermal cells of white, immature segments of maize leaf bases express the same reporter gene strongly. Morphologically, these epidermal cells look undifferentiated and are uniform in size and shape. When cultured for seven days on Murashige-Skoog medium [18], exised leaf base segments expand two-to threefold, and epidermal and guard cells differentiate and mature, regardless of whether or not the tissue is illuminated. Epidermal cells that differentiate in darkness continue to have the capacity to express the rbcS-m3::gusA reporter gene strongly. However, if the leaf base segments are illuminated after four to five days of expansion in darkness, but not before, these more mature epidermal cells are largely unable to express the same gene. That is, they acquire the characteristics of epidermal cells of green maize leaves with regard to expressing the rbcS-m3 reporter gene after undergoing a developmental program (in light or darkness) in vitro and after being exposed to light. White light but not red is effective. Suppression of expression in maize epidermal cells requires different rbcS-m3 sequences than in mesophyll cells [31].

Immature renal tubules are resistant to prolonged anoxia

ABSTRACT: Very few data are available regarding the decreased susceptibility of the developing kidney to anoxia. Therefore, the purpose of this study was to develop an experimental system that would allow comparison of an anoxic insult in immature and mature proximal tubule segments and to investigate the hypothesis that the developing kidney is resistant to anoxia as compared with the mature kidney. Suspensions of proximal tubules from immature (age 8–10 d) and mature (8–10 wk) rats were obtained. The purity of the tubule suspension from the immature rats was documented by villin staining. A common buffer solution was developed to compare results from the immature and mature tubules. To study the response of the tubules to anoxia, we subjected the tubule suspension from both the immature and mature rats to 15, 30, 45, and 60 min of anoxia. Lactate dehydrogenase release was measured to assess plasma membrane damage, and ATP levels were determined as an index of cellular energy. After a short anoxic insult (15 or 30 min), the percentage of lactate dehydrogenase release was not significantly different from mature tubules. After prolonged anoxia (45 and 60 min) lactate dehydrogenase release continued to increase, whereas membrane integrity stabilized in the immature tubules. ATP levels decreased in both immature and mature tubules after anoxia, but the decline of ATP was greater in the mature tubules, with a plateau at 20% of basal ATP levels as compared with 40% in the immature tubules. Therefore, the developing kidney is resistant to prolonged anoxia.

Gibberellic Acid Regulates Cell Wall Extensibility in Wheat (Triticum aestivum L.)

Mutations (Rht genes) blocking sensitivity to gibberellic acid (GA) were used to examine phytohormone mediated cell wall expansion in wheat (Triticum aestivum L.). Irreversible extensibility of immature leaf segments, as determined by stress/strain (instron) measurements, declined with Rht gene dose. Exogenous GA(3) significantly increased wall extensibility in the nonmutant controls but had no effect on the near-isogenic GA-insensitive genotypes. Furthermore, ancymidol, an inhibitor of gibberellin biosynthesis, diminished wall extensibility in the nonmutant control. Extensibility of immature segments was highly correlated with mature leaf sheath length (R = +0.95). The results indicate that wall yielding properties of expanding wheat leaves are associated with leaf cell expansion potential and that GA is involved in the determination of those properties.

Stage-specific antigens of Hymenolepsis microstoma recognized in BALB/c mice.

Antigenicity of eggs (oncospheres), cysticercoids and adults (with immature segments only) of the bile duct tapeworm Hymenolepsis microstoma was analysed using immunoblotting techniques and indirect immunofluorescent antibody (IFA) techniques with immune sera of BALB/c mice (i) infected with different doses of cysticercoids, (ii) during patent or prepatent infection with the lumen phase of the parasite or (iii) sensitized with live or dead eggs. Antibody responses detected by IFA test and immunoblotting showed that antigenicity of eggs (oncospheres) differed from that of cysticercoids and adults. Single worm infections were sufficient to stimulate antibody responses. Mice which had patent infection showed strong antibody responses to all three (egg (oncosphere), cysticercoid, adult) antigens, while mice given two prepatent infections showed some antibody responses to cysticercoid and adult antigens only. Although the normal intermediate hosts of this parasite are arthropods, antibodies to some major egg (oncosphere) antigens were produced in mice given eggs of this parasite orally, either through inoculation of eggs or ingestion of faeces contaminated with eggs. Antibodies were not produced in mice dosed with non-viable eggs. The results are consistent with the hypothesis that cestode parasites express phase- (or stage-) specific antigens.

International Travel by U.S. Conservation Groups and Professional Societies

The U.S. conservation organizations, together with the U.S. scientific and professional societies most closely allied to natural resources, are termed the “conservation sector.” This sector was surveyed to determine the volumes, destinations, objectives, and decisionmaking criteria for international travel. The resulting profile indicates a small, high-cost, and immature market segment driven mainly by the desire to provide educational and professional experiences.

The appearance of photosynthetic proteins in developing maize leaves

The appearance of photosynthetic proteins was directly measured in developing maize (Zea mays L.) leaves. Third leaves of 10-14-d-old seedlings were dissected into six successive sections from the basal meristem to the tip of the leaf. The membrane and soluble proteins were separated by polyacrylamide gel electrophoresis and then transferred onto cyanogen bromide paper. After transfer of membrane proteins the paper was reacted with antisera raised against the light-harvesting chlorophyll a/b protein of photosystem II, the chlorophyll a-binding protein of reaction center P-700 of photosystem I and the α-subunit of chloroplast-coupling factor 1. The blots of soluble proteins were reacted with antisera raised against the electron-transport proteins plastocyanin and Fe-NADP reductase (EC 1.6.7.1), the carbon-fixing enzymes ribulose-1,5-bisphosphate carboxylase (EC 4.1.1.39) and phosphoenolpyruvate carboxylase (EC 4.1.1.31), as well as pyruvate orthophosphate dikinase (EC 2.7.9.1). The schedule of appearance of proteins shows that the light-harvesting and ATP-generating proteins are present in the most immature segments at the leaf base and accumulate rapidly as the cells mature. The carbon-reducing enzymes, however, appear only in tissue that has differentiated into mesophyll and bundle-sheath cells.

Monoecocestus thomasi sp. n. (Cestoda: Anoplocephalidae) from the Northern Flying Squirrel, Glaucomys sabrinus (Shaw), in Oregon

Monoecocestus thomasi sp. n. (Cestoda: Anoplocephalidae), from the northern flying squirrel, Glaucomys sabrinus (Shaw), in Oregon, is described and distinguished from its congeners. Monoecocestus thomasi is the sixth species of Monoecocestus to be described from nearctic rodents, and the first from a member of the family Sciuridae. Our comparisons of taxonomic characters of the nominal species of Monoecocestus in North American rodents have shown that M. giganticus Buhler 1970 is a synonym of M. americanus (Stiles 1895), both from the porcupine, Erethizon dorsatum (Linnaeus). Insemination in Monoecocestus ssp. is discussed, with the conclusion that it takes place only by way of the vagina in early immature segments.

Methionine Metabolism and Ethylene Biosynthesis in Senescent Flower Tissue of Morning-Glory

In immature rib segments prepared from morning-glory (Ipomoea tricolor) flower buds, the major soluble metabolite formed from tracer amounts of l-methionine-U-(14)C was S-methylmethionine (SMM). In segments of senescing ribs, (14)C was progressively lost from SMM and appeared in free methionine. Immature segments contained about 4 nmoles of free methionine and about 16 nmoles of SMM per 30 segments. As the segments senesced, the methionine content increased about 10-fold while the SMM content remained unchanged; during this time about 0.8 nmole of ethylene was produced per 30 segments. Tracer experiments with l-methionine-U-(14)C, l-methionine-methyl-(3)H, and l-homocysteine thiolactone-(35)S indicated that SMM was capable of acting as a methyl donor, and that in senescent segments the methyl group was utilized for methionine production with homocysteine serving as methyl acceptor. Of the 2 molecules of methionine produced in this reaction, 1 was re-methylated to SMM, and the other contributed to the observed rise in the content of free methionine.Internal pools of methionine and SMM were prelabeled (but not significantly expanded) by overnight incubation on 10 mum l-methionine-U-(14)C. The specific radioactivity of the ethylene subsequently evolved during the senescence of the segments closely paralleled the specific radioactivity of carbon atoms 3 plus 4 of free methionine extracted from the tissue, demonstrating that methionine was the major precursor of ethylene in this system. The specific radioactivity of carbon atoms 3 plus 4 of extracted SMM was about twice that of the free methionine.Based on these results, a scheme for methionine biosynthesis in senescent rib tissue is presented. The operation of this pathway in the control of ethylene production is discussed.

Biosynthesis of Wound Ethylene in Morning-Glory Flower Tissue

Production of wound ethylene was investigated in rib segments excised from flower buds of morning-glory (Ipomoea tricolor). Segments of the ribs were cut from buds 2 days before flower opening, floated overnight on 5 mm KCl solution, and transferred to agar the following morning. These immature segments evolved only a small quantity of ethylene during incubation on agar, with most of the production occurring in the morning. When such segments were wounded mechanically early in the afternoon, the rate of ethylene production rose more than 10-fold within 1 hour and returned to a low rate after about 3 hours.Production of ethylene by both untreated and wounded rib segments was inhibited more than 95% by overnight pretreatment with the ethoxy analog of rhizobitoxine (3 x 10(-5) and 10(-4)m). After overnight exposure of segments to 9 muml-methionine-U-(14)C, the specific radioactivity of the ethylene evolved by untreated and wounded tissue was determined and compared to the specific radioactivities of carbon atoms 3 plus 4 of methionine and S-methylmethionine (SMM) extracted from the segments. The specific radioactivity of methionine was about one-half that of SMM; neither value was significantly affected by wounding. The specific radioactivity of ethylene evolved by untreated tissue was close to that of SMM. In wounded tissue the specific radioactivity of the ethylene evolved was lower, but still above that of methionine. These results are consistent with the interpretations that wound ethylene is synthesized from carbon atoms 3 plus 4 of either SMM or methionine. On the basis of earlier experiments with senescing rib segments, it is suggested that methionine serves as the precursor of the wound ethylene.