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PubMed1981

Differential Light Responses of Photosynthesis by Triazine-resistant and Triazine-susceptible Senecio vulgaris Biotypes.

Studies were conducted to determine a physiological basis for competitive differences between Senecio vulgaris L. biotypes which are either resistant or susceptible to triazine herbicides. Net carbon fixation of intact leaves of mature plants was higher at all light intensities in the susceptible biotype than in the resistant biotype. Quantum yields measured under identical conditions for each biotype were 20% lower in the resistant than in the susceptible biotype. Oxygen evolution in continuous light measured in stroma-free chloroplasts was also higher at all light intensities in the susceptible biotype than in the resistant biotype. Oxygen evolution in response to flashing light was measured in stroma-free chloroplasts of both biotypes. The steady-state yield per flash of resistant chloroplasts was less than 20% that of susceptible chloroplasts. Susceptible chloroplasts displayed oscillations in oxygen yield per flash typically observed in normal chloroplasts, whereas the pattern of oscillations in resistant chloroplasts was noticeably damped. It is suggested that modification of the herbicide binding site which confers s-triazine resistance may also affect the oxidizing side of photosystem II, making photochemical electron transport much less efficient. This alteration has resulted in a lowered capacity for net carbon fixation and lower quantum yields in whole plants of the resistant type.

Journal Article↗
PubMed1985

Altered Leaf Structure and Function in Triazine-Resistant Common Groundsel (Senecio vulgaris).

Anatomical and physiological characteristics of leaves of triazinesusceptible and -resistant biotypes of common groundsel (Senecio vulgaris L.) were studied in order to explain the differences in light-saturated photosynthetic rates previously reported. Leaves were of uniform leaf plastochron index from greenhouse-grown plants. Susceptible plants had greater leaf fresh and dry weights and leaf areas, while resistant plants had greater specific leaf mass (mg fresh weight/cm(2)). Susceptible plants had greater amounts of total chlorophyll per unit leaf weight and a higher chlorophyll a/b ratio. Soluble protein in leaves was higher in susceptible chloroplasts on a weight and area basis, but similar to resistant chloroplasts on a unit chlorophyll basis. Activity of ribulose 1,5-bisphosphate carboxylase was higher in resistant plants on a fresh weight, leaf area, and milligram chlorophyll basis. Stomatal frequency, length, and arrangement were similar between biotypes, as were transpiration and conductance. Resistant leaves had less air space (v/v), more cells in palisade and spongy mesophyll, and a greater volume of palisade tissue than spongy, when compared to susceptible leaves. Differences in leaf structure and function between biotypes are probably due to a complex of developmental adaptations which may be only indirectly related to modified photosystem II in resistant plants. These results indicate that the consistently lower rates of net photosynthesis and yield in resistant plants cannot be explained solely on the basis of these leaf characteristics. Several possible mechanisms to account for reduced productivity are suggested.

Journal Article↗
PubMed1988

Ornithine decarboxylase, polyamines, and pyrrolizidine alkaloids in senecio and crotalaria.

When tested for ornithine and arginine decarboxylases, pyrrolizidine alkaloid-bearing Senecio riddellii, S. longilobus (Compositae), and Crotalaria retusa (Leguminosae) plants exhibited only ornithine decarboxylase activity. This contrasts with previous studies of four species of pyrrolizidine alkaloid-bearing Heliotropium (Boraginaceae) in which arginine decarboxylase activity was very high relative to that of ornithine decarboxylase. Unlike Heliotropium angiospermum and Heliotropium indicum, in which endogenous arginine was the only detectable precursor of putrescine channeled into pyrrolizidines, in the species studied here-using difluoromethylornithine and difluoromethylarginine as the enzyme inhibitors-endogenous ornithine was the main if not the only precursor of putrescine converted into the alkaloid aminoalcohol moiety. In S. riddellii and C. retusa at flowering, ornithine decarboxylase activity was present mainly in leaves, especially the young ones. However, other very young organs such as inflorescence and growing roots exhibited much lower or very low activities; the enzyme activity in stems was negligible. There was no correlation between the enzyme activity and polyamine or alkaloid content in either species. In both species only free polyamines were detected except for C. retusa roots and inflorescence-with relatively very high levels of these compounds-in which conjugated putrescine, spermidine, and spermine were also found; agmatine was not identified by HPLC in any plant organ except for C. retusa roots with rhizobial nodules. Organ- or age-dependent differences in the polyamine levels were small or insignificant. The highest alkaloid contents were found in young leaves and inflorescence.

Journal Article↗
PubMed1988

Comparison of Triazine-Resistant and -Susceptible Biotypes of Senecio vulgaris and Their F(1) Hybrids.

The relationship of triazine resistance to decreased plant productivity was investigated in Senecio vulgaris L. F(1) reciprocal hybrids were developed from pure-breeding susceptible (S) and resistant (R) lines. The four biotypes (S, S x R, R, R x S) were compared in terms of atrazine response, electron transport, carbon fixation, and biomass production. Atrazine response, carbon fixation rate, and PSII and whole-chain electron transport rates of hybrids were nearly identical to those of their respective maternal parents. Significant differences occurred between the two susceptible (S, S x R) and two resistant (R, R x S) biotypes in atrazine response (I(50)), carbon fixation rate, and PSII and whole-chain electron transport rates; PSI rates were identical in all four biotypes. Coupled and uncoupled, whole-chain electron transport rates of thylakoids of the two susceptible biotypes were approximately 50% greater than those of the two resistant biotypes at photon flux densities greater than 215 micromoles per square meter per second. Carbon exchange rates of the two susceptible biotypes were 23% greater than those of the two resistant biotypes. Hybrid biotypes (S x R, R x S) were not identical to their maternal parents in biomass production. The S, S x R, and R x S plants all achieved greater biomass than R plants. These results suggest that while the resistance mutation influences thylakoid performance, reduced productivity of triazine-resistant plants cannot be ascribed solely to decreases in electron transport or carbon assimilation rates brought about by the altered binding protein. Since the F(1) hybrids differed from their maternal parents only in nuclear genes, it appears that the detrimental effects of the triazine resistance mutation on plant growth may be attenuated by interactions of the plastid and nuclear genomes.

Journal Article↗
PubMed1990

Triazine Resistance in Senecio vulgaris Parental and Nearly Isonuclear Backcrossed Biotypes Is Correlated with Reduced Productivity.

Isonuclear triazine-susceptible and triazine-resistant Senecio vulgaris L. biotypes were developed by making reciprocal crosses between susceptible and resistant biotypes to obtain F(1) hybrids and backcrossing the hybrids to the appropriate pollen parent. The electrophoretic isozyme patterns of the enzyme aconitase obtained from leaf extracts of triazine-susceptible parental (S) and backcrossed (SxR(BC6)) biotypes, and triazine-resistant parental (R) and backcrossed (RxS(BC6)) biotypes verified that the biotypes had the expected nuclear genomes. Atrazine inhibition of chloroplast whole chain electron transport from water to methyl viologen was measured to verify susceptibility or resistance to triazine herbicides. The photosynthetic rate and biomass accumulation of greenhouse grown susceptible and resistant S. vulgaris biotypes were measured 28, 35, 42, 50, 57, and 64 days after planting to determine the effect of altered chloroplast function. S and SxR(BC6) biotypes had CO(2) assimilation rates of 16.2 and 16.6 micromoles CO(2) per square meter per second, respectively, and I(50) values (herbicide concentration producing 50% inhibition) of about 0.49 micromolar atrazine. The corresponding values for the R and RxS(BC6) biotypes were 14.7 and 14.6 micromoles CO(2) per square meter per second with I(50) values of 65.0 micromolar atrazine. The S biotype was larger and more productive than the R biotype at all harvests. At the harvest 57 days after planting, mean shoot dry weight was 33.2 and 8.7 grams for the S and R biotypes, respectively. The growth effect associated with chloroplast differences was shown in comparisons of the S biotype with the RxS(BC6) biotype and of the SxR(BC6) biotype with the R biotype. The RxS(BC6) biotype had 72% of the shoot dry weight of the S biotype while the R biotype had 55% of the shoot dry weight of the SxR(BC6) biotype. The RxS(BC6) and R biotypes produced about 73 and 62% of the leaf area of the S and SxR(BC6) biotypes, respectively. Relative growth rate was similar in biotypes with the same nuclear genome; however, instantaneous unit leaf rate was higher in the S compared to the RxS(BC6) biotype and in the SxR(BC6) compared to the R biotype. At 57 days after planting, the cumulative leaf area duration (i.e. photosynthetic opportunity) of the RxS(BC6) and R biotypes was 86 and 66% of that of the S and SxR(BC6) biotypes, respectively. Our data indicate that impaired chloroplast function in triazine resistant S. vulgaris biotypes limits growth and productivity at the whole plant level.

Journal Article↗
PubMed1990

Stereochemical studies on algal pheromone biosynthesis. A model study with the flowering plant Senecio isatideus (Asteraceae).

Unsaturated C8 and C11 hydrocarbons act as chemical signals (chemotaxis) during sexual reproduction of many marine brown algae. One of these compounds, namely (+)-(6S)-6-(1Z-butenyl)cyclohepta-1,4-diene (= ectocarpene) is also formed as a major hydrocarbon by the flowering plant Senecio isatideus (Asteraceae). On administration of enantiospecifically labelled (8R)- or (8S)-[7,8-2H2]trideca-3,6,9-trienoic acid instead of the natural precursor dodeca-3,6,9-trienoic acid to this plant, the artificial C12 analogue of ectocarpene is formed. Mass spectroscopic analysis of the metabolites revealed this process to be enantiospecific for the C(8)-HRe atom of the precursor acid. The stereochemical course of the overall reaction is in agreement with a precise, U-shaped embedding of the trienoic acid into the active center of the enzyme(s) and Re-attack onto a hydrogen at the C(8) methylene group of this precursor. The reactive intermediate cyclizes by pi-orbital interaction between C(4) and C(6) of the acid and is accompanied by decarboxylation. The first product is a thermally unstable (1S,2R)-cis-1-(1E,3Z-hexadienyl)-2-vinylcyclopropane, which immediately rearranges to (+)-(6S)-ectocarpene (homo-Cope rearrangement). The present work provides first experimental evidence for a homo-Cope rearrangement as a naturally occurring electrocyclic reaction.

Cyclization↗
PubMed1977

Pyrrolizidine alkaloids: their occurrence in honey from tansy ragwort (Senecio jacobaea L.)

The hepatotoxic alkaloids known to occur in tansy ragwort (Senecio jacobaea L.) are also present in honey produced from the nectar of this species. These alkaloids, which inclued senecionine, seneciphylline, jacoline, jaconine, jacobine, and jacozine, are potentially carcinogenic, mutagenic, and teratogenic and may pose health hazards to the human consumer.

Food Contamination↗
PubMedDate not supplied

Alkaloids from the roots of Senecio macedonicus Griseb.

The new alkaloids 7-,9-diangeloylplatynecine (1) and 8-episarracine N-oxide (2), were isolated and identified from the roots of Senecio macedonicus. Another one, 8-epineosarracine was detected by GC/MS analyses of the crude alkaloid mixture. The cytotoxicity and biological activity of the alkaloids were tested on normal murine spleen lymphocytes and P3U1 mouse myeloma.

Animals↗
PubMed1982

Absorption and excretion of pyrrolizidine (Senecio) alkaloids and their effects on mineral metabolism in rabbits.

A metabolism study was conducted with rabbits to determine the effect of consumption of 5% dietary Senecio jacobaea (SJ) on tissue mineral levels and mineral excretion. Gastro-intestinal (GIT) absorption of pyrrolizidine alkaloids (PA) from SJ was also studied by monitoring excretion into urine and feces and by the use of ligated gut segments in vitro. Inclusion of SJ into a diet containing added Cu (100 ug/g) and Zn (100 ug/g) caused a 2.6-fold increase in liver Cu concentration (P less than .05), decreased total liver Zn (P less than .05), and increased plasma Fe (P less than .05) when compared with rabbits consuming the same diet without SJ. Fecal and urinary excretion of Cu and Zn were not markedly affected by the addition of Cu, Zn and(or) SJ to rabbit diets. Excretion of PA from SJ in the diet was not affected (P greater than .05) by the addition of Cu and Zn to the diet. The PA elimination was much greater in urine than feces (P less than .001). Isolated PA from SJ were found to be readily transferred across the mucosa of isolated everted sacs of jejunum and ileum in vitro against a concentration gradient. These results suggest that the effects of dietary SJ on alterations in mineral metabolism are not due to changes in GIT mineral elimination. In addition, it appears that the resistance of rabbits to dietary SJ intoxication is not caused by low GIT absorption of PA, but rather by efficient urinary elimination.

Animals↗
PubMed1983

Effect of sheep rumen fermentation and methane inhibition on the toxicity of Senecio jacobaea.

Senecio jacobaea (SJ) was incubated in sheep rumen fluid-buffer mixtures to determine if metabolism and(or) detoxication of pyrrolizidine alkaloids (PA) was occurring. The nontoxic reduction metabolite, 7 beta-hydroxy-l-methylene-8 alpha-pyrrolizidine, was not detected when SJ-rumen fluid incubation extracts were subjected to high performance liquid chromatography and mass spectrographic analysis. Rats were used as assay animals in another experiment to assess the toxicity of SJ incubated in rumen fluid. Incubation treatments were: Rumen fluid (RF) from a sheep not fed SJ (RF-0); RF autoclaved before incubation (RF-0A); RF from sheep fed 50% SJ for 1 wk (RF-1); RF from a sheep fed 50% SJ for 5 wk (RF-5), and RF-5 with 5 microM iodoform in the incubation medium (RF-5I). The SJ treatments were included in rat diets at the 10% level. Dietary treatment and mean rat survival times (days) were: control, no mortality; 10% untreated SJ, 43; RF-0, 53; RF-0A, 55; RF-1, 44; RF-5, 56; RF-5I, 44, There were no significant differences in survival time. This indicates that SJ was not detoxified as a result of incubation in sheep RF in vitro, and suggests that rumen detoxification does not account for resistance of sheep to SJ. The pH and volatile fatty acid concentrations of the incubation mixtures were measured before and after incubation. Acetate/propionate and pH following incubation were respectively: RF-0A, 7.3, 4.3; RF-0, 4.2, 4.4; RF-1, 2.7, 4.5; RF-5, 2.6, 4.5; RF-5I, 2.4, 4.5. These data show that although pretreatment of the rumen fluid donor with dietary SJ and addition of iodoform to the incubation mixture favor reductive rumen metabolism, detoxification of PA from SJ does not occur during in vitro sheep rumen fermentation.

Animals↗
PubMed1983

Effect of phenobarbital on toxicity of pyrrolizidine (Senecio) alkaloids in sheep.

The effect of prolonged phenobarbital (PB) administration on the toxicity of Senecio jacobaea (SJ) was studied in sheep. Hepatic microsomal mixed function oxidase (MFO) activity was monitored. Pentobarbital sleeping times were decreased after 17 d of treatment, indicating initial induction of MFO. At 105 d of treatment, hepatic microsomal aminopyrine N-demethylase activity and cytochrome P-450 levels were increased (P less than .05) as a result of PB administration. No differences (P greater than .05) were observed in activity of microsomal epoxide hydrolase, glutathione S-transferase or liver glutathione as a result of SJ and (or) PB. Epoxide hydrolase activity in control sheep was about fivefold higher than values previously reported for rats. Liver Cu concentration was increased (P less than .05) in sheep receiving PB and SJ when compared with controls, but no differences (P greater than .05) were observed in the hepatic intracellular distribution of Cu as a result of PB and(or) SJ. Histopathological examination of liver revealed greater incidence and severity of lesions in animals receiving SJ, but PB did not appear to potentiate SJ intoxication. The results suggest that MFO induction by PB does not increase the susceptibility of sheep to SJ intoxication. Sheep possess a high activity of hepatic microsomal epoxide hydrolase which could account for their resistance to SJ intoxication.

Aminopyrine N-Demethylase↗
PubMed2000

Routes of origin of two recently evolved hybrid taxa: Senecio vulgaris var. hibernicus and York radiate groundsel (Asteraceae).

The possible pathways of origin of two recently arisen introgressant forms of Senecio vulgaris (i.e., var. hibernicus and York radiate groundsel) were investigated in experimental crosses between tetraploid S. vulgaris var. vulgaris and the normally diploid S. squalidus. Comparison of the morphology of synthesized hybrid progeny with established taxa, by discriminant function analysis, revealed that fertile hybrid offspring similar in morphology to S. vulgaris var. hibernicus and York radiate groundsel could be synthesized: (1) following formation of genomically stable diploid gametes by the triploid hybrid; (2) through the production of unreduced gametes by diploid S. squalidus; and (3) when a tetraploid form of S. squalidus acted as one of the parents. It was evident that hybrid offspring similar in morphology to the two introgressant taxa were more often produced in backcrosses to S. vulgaris than in segregating F2 or F3 generations (53% as opposed to 36%), and that fertile hybrid progeny were formed within two generations. Because hybridization between S. vulgaris and S. squalidus occurs regularly, although at very low frequency, in natural mixed populations in the British Isles, there is the potential for multiple origins to occur in the wild of both S. vulgaris var. hibernicus and York radiate groundsel.

Journal Article↗
PubMed1986

Clinicopathologic study of horses surviving pyrrolizidine alkaloid (Senecio vulgaris) toxicosis.

Twenty horses of various ages had inadvertently ingested alfalfa hay contaminated with Senecio vulgaris. Among them, 4 died of liver disease. Blood was collected from affected horses at monthly intervals for 7 months and at the 9th and 14th months. The following serum enzymes and chemical items were assayed: aspartate aminotransferase, lactate dehydrogenase, alkaline phosphatase, gamma-glutamyl transferase, sorbitol dehydrogenase, total bilirubin, BUN, glucose, cholesterol, inorganic phosphate, calcium, total protein, and albumin. Amino acid profiles, conjugated bile acids, sulfobromophthalein clearance times, and liver histopathologic changes via serial biopsies were also monitored. Liver histopathologic changes revealed lesions progressively increasing in severity. Aspartate aminotransferase and plasma amino acid ratios indicated chronic liver degeneration (0.05 level of significance). gamma-Glutamyl transferase and lactate dehydrogenase as well as BUN values fluctuated, but returned to within reference values. Horses appeared clinically normal 14 months after intoxication, but were unable to tolerate stress of exercise.

Amino Acids↗
PubMedDate not supplied

Microsomal metabolism of pyrrolizidine alkaloids from Senecio jacobaea. Isolation and quantification of 6,7-dihydro-7-hydroxy-1-hydroxymethyl-5H-pyrrolizine and N-oxides by high performance liquid chromatography.

The metabolism in vitro of four pyrrolizidine alkaloids from the poisonous plant Senecio jacobaea was studied. The pyrrolizidine alkaloids jacobine, jacoline, senecionine, and seneciphylline, all macrocyclic diesters of retronecine, were incubated with rat liver microsomes. Analysis of incubation extracts by HPLC with a PRP-1 reverse phase styrene-divinylbenzene resin column revealed the presence of two major metabolites, 6,7-dihydro-7-hydroxy-l-hydroxymethyl-5H-pyrrolizine and an N-oxide derivative. Mass spectrometry was used to confirm the structure of metabolites isolated by preparative HPLC using the PRP-1 column and a C-8 reverse phase column. Quantitative HPLC analysis using the PRP-1 column allowed the comparison of the rates of formation of the dihydropyrrolizine derivative and N-oxides from the four alkaloids.

Animals↗
PubMed1988

Delayed manifestation of Senecio-induced pyrrolizidine alkaloidosis in cattle: case reports.

Selected case reports from closely controlled experimental feedings of Senecio jacobaea (tansy ragwort), S longilobus (threadleaf groundsel) and S riddellii (Riddell's groundsel) to cattle are presented to show that all 3 of these pyrrolizidine alkaloid-containing plants may not necessarily induce proximate toxicity, but may cause typical signs and death many months after the plants are ingested. Results of the experimental intoxications indicate that if the daily dosage is of sufficient size to insult hepatocytes, a chronic lethal dose of plant may be eaten in only a few days. Early signs of intoxication may be absent, or mild and transitory, and serum enzyme changes that reflect liver injury may not always be detectable. Latent pyrrolizidine alkaloidosis signs can develop many months after the plants are eaten, and death imminent soon thereafter. The prepatent period and eventual time of death appears to be dependent on the time-dose relationship that determines the rate of progressive hepatocellular injury.

Animals↗