Characteristic thickened cell walls of the bracts of the 'eternal flower' Helichrysum bracteatum

Background and Aims

Helichrysum bracteatum is called an ‘eternal flower’ and has large, coloured, scarious bracts. These maintain their aesthetic value without wilting or discoloration for many years. There have been no research studies of cell death or cell morphology of the scarious bract, and hence the aim of this work was to elucidate these characteristics for the bract of H. bracteatum.

Methods

DAPI (4''6-diamidino-2-phenylindol dihydrochloride) staining and fluorescence microscopy were used for observation of cell nuclei. Light microscopy (LM), transmission electron microscopy (TEM) and polarized light microscopy were used for observation of cells, including cell wall morphology.

Key Results

Cell death occurred at the bract tip during the early stage of flower development. The cell wall was the most prominent characteristic of H. bracteatum bract cells. Characteristic thickened secondary cell walls on the inside of the primary cell walls were observed in both epidermal and inner cells. In addition, the walls of all cells exhibited birefringence. Characteristic thickened secondary cell walls have orientated cellulose microfibrils as well as general secondary cell walls of the tracheary elements. For comparison, these characters were not observed in the petal and bract tissues of Chrysanthemum morifolium.

Conclusions

Bracts at anthesis are composed of dead cells. Helichrysum bracteatum bracts have characteristic thickened secondary cell walls that have not been observed in the parenchyma of any other flowers or leaves. The cells of the H. bracteatum bract differ from other tissues with secondary cell walls, suggesting that they may be a new cell type.Key words: Helichrysum bracteatum, scarious bract, secondary cell wall, primary cell wall, cell morphology, birefringence, orientated cellulose microfibrils, cell death, DAPI, transmission electron microscopy, polarized light microscopy     

Morphinan alkaloids in Papaver bracteatum: Biosynthesis and fate

The known metabolic pathway for hydrophenanthrene alkaloids in Papaver somniferum has been examined for occurrence in P. bracteatum, a species reported to contain thebaine but no codeine or morphine. 1,2-Dehydro-reticulinium-[3-¹⁴C] chloride and (±)-reticuline-[3-¹⁴C] were fed to P. bracteatum plants and both were incorporated, the former into reticuline and thebaine and the latter into thebaine, suggesting that thebaine biosynthesis is the same in the two species. Studies of the natural abundance of morphinan alkaloids in P. bracteatum and the results from feeding codeinone-[16-³H] and codeine-[16-³H] indicate that this species can reduce codeinone to codeine but can not perform either of the demethylations to produce codeinone or morphine. Fed thebaine-[16-³H] was substantially metabolized but not by pathways that involved demethylations to either oripavine or northebaine.     

Alkaloids of Papaver bracteatum: 14-β-hydroxycodeinone, 14-β-hydroxycodeine and N-methylcorydaldine

Three new alkaloids have been identified from Papaver bracteatum, 14-β-hydroxycodeinone, 14-β-hydroxycodeine and N-methylcorydaldine. The presence of alpinigenine was also confirmed.     

Orientalidine and isothebaine from cell cultures of Papaver bracteatum

Orientalidine, isothebaine and sanguinarine were isolated from callus cultures of Papaver bracteatum when grown on M & S medium with various horm     

Enzymic reduction of codeinone in vitro cell-free systems from Papaver somniferum and P. Bracteatum

Cell-free extracts have been prepared from Papaver somniferum which catalyze the reduction of codeinone-[16-³H] to codeine. The methodology for examining this conversion has pointed to conditions for exploring the preparation of suitable enzyme extracts. P. bracteatum also yielded a cell-free system which reduced codeinone to codeine, both of which are foreign to this species.     

Alpinine,epialpinine and other alkaloids from Papaver bracteatum

Alpinine, epialpinine, muramine and protopine were identified as alkaloids of Papaver bracteatum. The earlier reported presence of alpinine is revised. The structures of codeine and neopine, earlier reported for this species, are assessed. Screening for the presence of O-methylflavinantine was negative.     

Neodihydrothebaine and bractazonine,two dibenz[d,f]azonine alkaloids of Papaver bracteatum

Two new dibenz[d,f]azonine alkaloids, neodihydrothebaine and bractazonine were isolated from Papaver bracteatum. Their possible biosynthesis from thebaine is discussed. The structures of both new alkaloids are proven by synthesis. An isomeric dibenz[d,f]azonine compound was also prepared.     

Identification and Phytotoxicity Assessment of Phenolic Compounds in Chrysanthemoides monilifera subsp. monilifera (Boneseed)

Chrysanthemoides monilifera subsp. monilifera (boneseed), a weed of national significance in Australia, threatens indigenous species and crop production through allelopathy. We aimed to identify phenolic compounds produced by boneseed and to assess their phytotoxicity on native species. Phenolic compounds in water and methanol extracts, and in decomposed litter-mediated soil leachate were identified using HPLC, and phytotoxicity of identified phenolics was assessed (repeatedly) through a standard germination bioassay on native Isotoma axillaris. The impact of boneseed litter on native Xerochrysum bracteatum was evaluated using field soil in a greenhouse. Collectively, we found the highest quantity of phenolic compounds in boneseed litter followed by leaf, root and stem. Quantity varied with extraction media. The rank of phenolics concentration in boneseed was in the order of ferulic acid > phloridzin > catechin > p-coumaric acid and they inhibited germination of I. axillaris with the rank of ferulic acid > catechin > phloridzin > p-coumaric acid. Synergistic effects were more severe compared to individual phenolics. The litter-mediated soil leachate (collected after15 days) exhibited strong phytotoxicity to I. axillaris despite the level of phenolic compounds in the decomposed leachate being decreased significantly compared with their initial level. This suggests the presence of other unidentified allelochemicals that individually or synergistically contributed to the phytotoxicity. Further, the dose response phytotoxic impacts exhibited by the boneseed litter-mediated soil to native X. bracteatum in a more naturalistic greenhouse experiment might ensure the potential allelopathy of other chemical compounds in the boneseed invasion. The reduction of leaf relative water content and chlorophyll level in X. bracteatum suggest possible mechanisms underpinning plant growth inhibition caused by boneseed litter allelopathy. The presence of a substantial quantity of free proline in the target species also suggests that the plant was in a stressed condition due to litter allelopathy. These findings are important for better understanding the invasive potential of boneseed and in devising control strategies.     

Bound forms of alkaloids in Papaver somniferum and P. Bracteatum

The polysaccharide fraction of the pericarp and seed of Papaver somniferum were shown to contain bound forms of morphine which were derived from radioactive morphine fed to living plants. Bound forms of codeine, thebaine and some unidentified alkaloid-like compounds were also detected in the pericarp and bound thebaine occurred in the pericarp of Papaver bracteatum. The complexity and molecular weight of the bound alkaloids seemed to increase during ripening, and it is suggested that these substances represent transitional forms in the metabolism and transiocation of morphine from latex to seed.     

Constituents of Papaver bracteatum: O-methyl-α-thebaol and 10-n-nonacosanol. Lanthanide-induced chemical shifts in 1H NMR and 13C NMR

Two non-alkaloidal constituents were identified in Papaver bracteatum: O-methyl-α-thebaol and 10-n-nonacosanol. O-Methyl-α-thebaol is a new natural compound. The presence of isothebaine is confirmed. Lanthanide-induced chemical shifts can be used for the assignments of the ₁₃C NMR chemical shifts of isothebaine and phenanthrenes. The use of lanthanide-induced chemical shifts in the identification of methoxyl resonances in ₁H NMR is discussed.     

A rapid quantitative method for the determination of thebaine in Papaver bracteatum

A rapid method enabling a quantitative analysis of thebaine in capsules and latex of Papaver bracteatum has been devised, based on a TLC technique. This method was compared to the commonly used GLC procedure, and highly significant correlation coefficient (r = 0.90) and linear regression were found between the two methods. Values for concentrations to the nearest ±0.25% of the standard spots can be reached by this simple and rapid thebaine determination.     

Plasmopara invertifolia sp. nov. causing downy mildew on Helichrysum bracteatum (Asteraceae)

Plasmopara invertifolia sp. nov. causes severe leaf distortion and necrosis on Helichrysum bracteatum, a beautiful and important ornamental plant for trade in Brazil. This oomycete pathogen is distinguished from other species of Plasmopara on Asteraceae by its smaller sporangia and larger sporangiophores, which justifies the proposition of a new taxon in the genus Plasmopara to accommodate it. The phylogenetic analysis of cox2 gene sequence data supports such placement and also shows that P. invertifolia is close to the P. halstedii complex. Plasmopara invertifolia is then described, illustrated and discussed.     

Cellular and subcellular compartmentation of Ni in the Eurasian serpentine plants Alyssum bracteatum, Alyssum murale (Brassicaceae) and Cleome heratensis (Capparaceae)

This study investigated the cellular and subcellular compartmentation of Ni in the Eurasian serpentine species Alyssum murale, Alyssum bracteatum and Cleome heratensis and a non-serpentine population of A. murale (as a control) grown in hydroponic culture. Plant growth responses and Ni uptake clearly revealed the higher Ni tolerance of serpentine plants than the non-serpentine plants. Serpentine A. murale and A. bracteatum grew better at elevated (0.01 mM) Ni in the nutrient solution, supporting the view that the Ni hyperaccumulators have a higher requirement for Ni than normal plants. Low shoot Ni content of C. heratensis in response to the high Ni treatments indicated that this species employs an avoidance strategy for Ni tolerance. Energy-dispersive X-ray microanalysis showed that Ni was highly concentrated in the cell walls and cell lumen, most likely the vacuoles, of leaf epidermis of A. murale and A. bracteatum rather than in the mesophyll cells. EDX spectra from leaves of the non-serpentine A. murale suggested that Ni accumulated in both epidermal and mesophyll cells but not in the epidermal cell walls. Growth reduction and Ni toxicity in plants of the non-serpentine A. murale could be due to accumulation of Ni in the lumen of leaf mesophyll cells. Our data suggest that cellular and subcellular compartmentation are both possible mechanisms for Ni tolerance employed by the serpentine A. murale and A. bracteatum.     

Plant regeneration and thebaine content of plants derived from callus culture of Papaver bracteatum

Plants have been regenerated from embryogenic callus cultures of two varieties of Papaver bracteatum and successfully transplanted to soil. Regeneration occurred in good yield, around 40 plants to soil within 5 months per 0.4g piece of original callus. Thebaine concentrations comparable to those in seed-grown plants were obtained in callus-derived plants. It is suggested that there is potential for mass micropropagation of P. bracteatum, which may be useful in developing agriculturally-improved lines.Abbreviations MS Murashige and Skoog (1962) basal medium     

Papaver bracteatum,potential commercial source of codeine

Papaver bracteatum, native to Iran and southern Russia, has been grown successfully in many countries. Research in the northwest United States has confirmed the potential for its commercial production as a source of the alkaloid thebaine. Potential for the chemical conversion of thebaine into codeine, one of man’s most widely used alkaloidal medicinal agents, is reviewed. Economic and social advantages of growing this species over opium poppy (Papaver somniferum) are discussed. The value of the seed oil for cooking and industrial use is considered.     

Pohlia integra (Card.) Shaw a neglected species,recorded from southern Africa and South America

Abstract

Mniobryum bracteatum Bartr. from Ecuador is reduced to a synonym of Pohlia integra (Card.) Shaw, previously known only from Mexico. The species, characterized by the occurrence of rhizoidal tubers, is also recorded from Bolivia and southern Africa.     

LATICIFER ULTRASTRUCTURE AND DIFFERENTIATION IN SEEDLINGS OF PAPAVER BRACTEATUM LINDL., POPULATION ARYA II (PAPAVERACEAE)

Laticifers of Papaver bracteatum Lindl., population Arya II, seedlings were examined by electron microscopy. Laticifers were first differentiated in procambium of the radicle associated with phloem about 72 hr after seeds were sown. Proliferation of membrane-bound vesicles of apparent endoplasmic reticulum origin distinguished laticifers from adjacent cells. Vesicles developed electron-dense caps from the internal condensation of small particles. Laticifer initials possessed the usual complement of organelles that became obscured in mature cells by the large, closely packed vesicles. Plastids contained an electron-dense, membrane-bound inclusion, but never developed lamellae or starch grains. Articulation and anastomoses between laticifer elements resulted from gradual removal of wall materials by both cells on opposite sides of the common walls at a perforation site. Differentiation of the laticifer initials and the micromorphology of the protoplast of P. bracteatum is similar to that reported for P. somniferum.