Reassessing the role of phospholipase D in the Arabidopsis wounding response

Plants respond to wounding by means of a multitude of reactions, with the purpose of stifling herbivore assault. Phospholipase D (PLD) has previously been implicated in the wounding response. Arabidopsis ( Arabidopsis thaliana ) AtPLD α 1 has been proposed to be activated in intact cells, and the phosphatidic acid (PA) it produces to serve as a precursor for jasmonic acid (JA) synthesis and to be required for wounding-induced gene expression. Independently, PLD activity has been reported to have a bearing on wounding-induced MAPK activation. However, which PLD isoforms are activated, where this activity takes place (in the wounded or non-wounded cells) and what exactly the consequences are is a question that has not been comprehensively addressed. Here, we show that PLD activity during the wounding response is restricted to the ruptured cells using ³²P_i-labelled phospholipid analyses of Arabidopsis pld knock-out mutants and PLD -silenced tomato cell-suspension cultures. pldα1 knock-out lines have reduced wounding-induced PA production, and the remainder is completely eliminated in a pldα1 / δ double knock-out line. Surprisingly, wounding-induced protein kinase activation, AtLOX2 gene expression and JA biosynthesis were not affected in these knock-out lines. Moreover, larvae of the Cabbage White butterfly ( Pieris rapae ) grew equally well on wild-type and the pld knock-out mutants.     

Chimerism following fusion in a clonal ascidian (Urochordata)

Many marine invertebrates bud vegetatively to produce a modular colony of individuals derived from a single zygote. Fusion of different colonies to produce a genetically composite entity (a chimera) is known from experiments on sponges, hydroids, corals, bryozoans and ascidians – groups which together dominate sessile faunas on marine hard substrates. Random amplified polymorphic DNA–polymerase chain reaction (RAPD–PCR) analysis was applied to individual modules (zooids) dissected from colonies of a colonial ascidian, Diplosoma listerianum (Milne Edwards), to investigate the presence and extent of chimerism. The technique revealed chimerism in wild material. In total, 288 colonies from eight different natural populations were analysed. Chimeric colonies were present in all populations, at frequencies of up to 61%, with up to six different genotypes present in some colonies. Zooids of different genetic origin often intermingled within a chimeric colony to produce a zooidal mosaic. Although fusion of colonies has been observed directly in the laboratory, an unknown proportion of the chimerism detected in wild populations might have arisen through somatic mutation. To assess this possibility, tissue of 12 clones in culture was sampled repeatedly over a period of 3 years and subjected to RAPD–PCR analysis. RAPD banding patterns were generally very stable; the changes noted mostly involved minor bands that would not, on their own, have been taken as evidence for chimerism under the conservative criteria adopted for the study of wild populations. It was concluded that a large proportion of natural chimerism is attributable to colony fusion.  © 2003 The Linnean Society of London. Biological Journal of the Linnean Society , 2003, 79 , 183–192.     

Die Hemmung der lichtinduzierten Chlorophyll-, Carotinoid- und Anthocyansynthese durch Äthanol

The Inhibition of the Light Induced Chlorophyll, Carotenoid and Anthocyan Synthesis by Ethanol. It is shown that already low concentrations of ethanol inhibit the light induced formation of pigments (chlorophylls, carotenoids, anthocyanins) in Raphanus-seedlings. The degree of inhibition depends on the ethanol concentration and rises with increasing incubation period. The inhibition of pigment synthesis is reversible, and immediately ceases when ethanol is removed. The formation of chlorophylls and anthocyanin is more repressed than that of carotenoids, and the formation of β-carotene to a higher extent than that of xanthophylls. It is concluded that ethanol inhibits pigment formation by inhibition of protein synthesis. These results indicate that ethanol and other lower alcohols cannot be used for the solubilizing of organic compounds when these are applied to plant tissues.     

Approaches to improve stress tolerance using molecular genetics

Plant productivity is greatly affected by environmental stress factors. In this review, we give an overview of molecular approaches that have been taken to study stress tolerance; in particular, we consider drought, salt and cold stress. Strategies and perspectives in using molecular biology to improve stress tolerance are outlined describing specific examples. Osmotic stress is associated with the synthesis of novel polypeptides and/or osmolytes. The spectrum and action of these different metabolites are summarized. A number of stress-related genes have been characterized and several representatives are discussed. After transforming plants with these genes, the effect of the encoded proteins on altered stress behaviour is examined. If genes with enzymatic functions were chosen for these experiments, complete pathways may be altered and this can implement the production of novel metabolites conferring stress tolerance.     

Surface Charge of Trypanosoma cruzi. Binding of Cationized Ferritin and Measurement of Cellular Electrophoretic Mobility*

SYNOPSIS The surface charge of epimastigote and trypomastigote forms of Trypanosoma cruzi was evaluated by means of binding of cationized ferritin to the cell surface as visualized by electron microscopy, and by direct measurements of the cellular microelectrophoretic mobility (EPM). Epimastigote forms had a mean EPM of -0.52 μm^.s^-1.V^-1.cm and were lightly labeled with cationized ferritin. In contrast, bloodstream trypomastigotes had a much higher EPM (-1.14), and the surface was heavily labeled with cationized ferritin. When trypomastigotes from stationary phase cultures were isolated on DEAE cellulose columns, the mean EPM was found to be significantly lower (-0.63), and labeling with cationized ferritin decreased. With a mixed population containing epimastigote, trypomastigote, and intermediate forms, EPM values ranging between -0.70 to -1.14 were found. From these observations we conclude that there is a definite increase in negative surface charge during development from epi- to trypomastigote forms of T. cruzi.     

Identification of adult females of Tinodes in Britain (Trichoptera: Psychomyiidae)

Abstract A key is provided to the females of the eight species of Tinodes recorded from Britain: Tinodes assimilis, T.dives, T.maclachlani, T.maculicornis, T.pallidulus, T.rostocki, T.unicolor, T.waeneri . The genital segments are described and notes given on mating and egg-laying.     

Pathogenic and Non-pathogenic Entamoeba: Pore Formation and Hemolytic Activity1

Pore-forming activity in planar lipid bilayers and liposomes of extracts from differentially pathogenic Entamoeba and the-capacity of trophozoites and subcellular fractions to lyse human red blood cells (hrbc) were investigated. In all amebas studied, the two activities paralleled each other. They were high in E. histolytica irrespective of the virulence of the particular strain, but low in non-pathogenic E. histolytica-like amebas of human origin as well as in E. invadens, which is pathogenic for reptiles, and in E. moshkovskii isolated from sewage. We conclude that the capacities to insert pores and to lyse are not sufficient for virulence although they may be necessary. The subcellular distribution of the hemolytic activity of E. histolytica and its sensitivity to a variety of inhibitors and activators differ from those of other known amebic cytotoxic activities including pore formation. Therefore, there may be an additional constituent of E. histolytica involved in the cytotoxicity of the parasite.     

Physiology and Chemistry of Substances Accelerating Abscission in Senescent Petioles and Fruit Stalks

Senescent petioles of Coleus rehneltianus Berger. Phaseolus vulgaris L. cv. Saxa. Acer pseudoplatanus L., and senescent fruit stalks of Malus domestica Borkh. cv. Golden Delicious contain at least three abscission accelerating substances, which were isolated by extraction with methanol or with water and by diffusion into agar. They were purified by thin-layer chromatography and bioassayed in a special abscission test using Coleus explants. Two of these abscission accelerators could be conclusively identified by thin-layer chromatography and by gas chromatography as abscisic acid and xanthoxin. The third substance, which has acidic properties and is less polar than abscisic acid, could not be identified. The concentration and the absolute amount of abscisic acid in Coleus petioles were found to decrease during their development, young petioles having the highest concentration. No evidence was found that the three abscission accelerators or synthetic abscisic acid and xanthoxin affect the production of ethylene in Caleus explatns. The results obtained do not support the hypothesis that senescent petioles contain a specific “senescence factor”, which stimulates abscission via ethylene production.