Beitrag zur Ätiologie der Hexenbesenkrankheit der KakteeOpuntia tuna (=tuna monstrosa)

Summary Mycoplasma-like bodies, as well as virus-like particles, were observed in phloem elements ofOpuntia tuna monstrosa. The mycoplasma-like bodies, but not the virus-like particles, disappeared in tetracycline hydrochloride treated plants, which indicated a mycoplasma etiology of the witches' broom disease ofOpuntia tuna.

---

---

This investigation was supported, in part, by a grant from the National Science Foundation No. GB-11861, Washington, D.C.     

Toxic substances produced byFusarium. III. Production and screening of phytotoxic substances ofF. oxysporum f. sp.carthami responsible for the wilt disease of safflowerCarthamus tinctorius Linn.

Summary Fusarium oxysporum f. sp.carthami, a causative agent for the wilt disease of safflower (Carthamus tinctorius Linn.), has been shown to produce diacetoxyscirpenol, T-2 toxin, fusaric acid and lycomarasmin in artificial media. These substances produced disease syndromes, similar to those seen after the natural infection, when administered in healthy plants. Diacetoxyscirpenol and T-2 toxin have been detected in diseased safflower plants after inoculating with the wilt pathogen. This study is the first demonstration of vivotoxicity of diacetoxyscirpenol.     

Effects of feeding on healthy and diseased corn plants on a vector and on a non-vector insect

Insect-transmitted plant pathogens can have positive, negative or no effects on the vector insect. Effects could be direct (caused by the pathogen) or indirect (mediated by changes in the plant). Pathogen effects on non-vector insects are less well known.Peregrinus maidis (Ashmead) (Homoptera: Delphacidae), an insect that is not a vector of the corn stunt spiroplasma (CSS), weighed less 15 days after feeding on CSS-infected corn plants relative to insects feeding on healthy corn plants. Fecundity of non-vector insects that were removed from diseased plants was higher than for insects coming from healthy plants. ForDalbulus maidis (DeLong & Wolcott) (Homoptera: Cicadellidae), an insect that transmits CSS, there were no differences in weight, longevity, eggs per day, weekly or total fecundity after feeding on healthy or on CSS-infected corn plants. Significant differences in some phloem amino acids were detected between healthy and CSS-infected plants. Infected plants also showed an increased phloem acidity as disease symptoms progressed. Feeding on CSS-infected corn plants by an insect that does not vector the pathogen infecting the plant can have favorable consequences as evidenced by an increased fecundity.Scientific aritcle no. 8819, contribution no. A-6605 of the Maryland Agricultural Experiment Station.     

Einfluss der Wurzeln auf die Trigonellinsynthese beiCoffea arabica

Summary Young plants ofCoffea arabica were fed 200 µC C¹⁴O₂ each, the carbon dioxide being absorbed by photosynthesis. The specific activity of the alkaloid trigonelline contained in the leaves was shown to be strongly dependent of leaf age. Excised plants without root system or plants with an interrupted shoot-root connection as regards pholem transport (by girdling the stem below the cotyledons) incorporate more radioactive carbon into the molecule of trigonelline than intact plants.     

Ein Virus als Erreger der Rollkrankheit der Rebe

Summary A virus has been isolated from grape vines diseased with leaf roll which is the cause of this dangerous illness in vineyards. This was proved by means of electromicrographs of the virus particles in pressed juices of all the diseased vine crops examined. The virus is only transmissible by graft and not by juice.     

Cyclohexadienones-insect growth inhibitors from the foliar surface and tissue extracts ofSenecio cannabifolius

Dewaxed leaf surface extracts of 12 plants from Hokkaido, prepared by dipping fresh leaves in chloroform for 3 min, were used in a choice leaf-disk bioassay against larvae of the tobacco cutwormSpodoptera litura. Activity was found only in the extract ofSenecio cannabifolius, a very successful weed in Hokkaido. Individual fractions of the extract, however, were not active. Incorporation of the individual fractions of the surface extracts as well as fractions of the methanolic extracts of the leaf residue into an artificial diet fed to neonateS. litura led to the isolation of ethyl (1-hydroxy-4-oxocyclohexa-2,5-dien-1-yl) acetate, the major surface compound, as the active principle. This compound was also present in the methanolic extract of the leaf residue together with methyl (1-hydroxy-4-oxocyclohexa-2,5-dien-1-yl) acetate, which had the same growth inhibitory effect on the larvae. The presence of these compounds in the foliar surface and tissue suggests a defensive role against herbivores.     

An evaluation of a somaclone ofDioscorea floribunda Mart & Gall

Summary 150 plants ofD. floribunda representing a single clone were regenerated from a stem tissue culture and regenerants were subjected to cytological, phenotypic and biochemical analysis from the pre-transfer stage to three vegetative growth cycles in the field. The plants could be subdivided into three cytological categories, namely, diploid, mosaic and tetraploid. Diploids, mosaics and the one tetraploid showed diversity amongst themselves with respect to internode length, content of chlorophyll and diosgenin. No marked difference in the length and nature of the leaf or in the type of stoma was recorded. Possible causes of the observed variation are discussed.     

Distribution of chlorophyllase activity and levels of chlorophylls a and b in sandal (Santalum album L.) affected by spike disease

Summary Compared to healthy specimens, the levels of chlorophylls a and b and the activity of chlorophyllase towards the two pigments remained lower in the leaves of spiked sandal at all stages of leaf development, except in the senescing diseased leaves where the chlorophyllase activity showed a steep rise.     

Reduction in bean common mosaic virus (BCMV) infectivity vis-a-vis crude leaf extract of some higher plants

Summary Crude leaf extracts of 17 plants were tested for their antiviral activity against BCMV. An extract ofAzadirachta indica A. Juss. was found to be most potent in reducing the infectivity of the virus.Authors are thankful to Dr R. D. Joshi for his valuable guidance and Prof. S. N. Mathur for providing lab facilities. Financial assistance by U. G. C. and C. S. I. R. is gratefully acknowledged.     

Tissue culture ofCynodon dactylon

Resumen Se indujo la formación de callos en nudos, entrenudos, vainas e inflorescencias deCynodon dactylon (L.) Pers. en un nutritivo que contenía 2 mg/l de 2,4-D. Los callos se subcultivan desde hace tres años en el mismo medio. Cuando se disminuyó la concentración de 2,4-D se produjo diferenciación de raíces pero los intentos para diferenciar yemas no tuvieron éxito. La adición de 6-bencil-adenina al medico indujo una pigmentación roja en los tejidos.

---

---

Publicación técnica Fis. No. 121, C.I.C.A.     

Gigantenone,a novel sesquiterpene phytohormone mimic

Summary Gigantenone, a new eremophilane diepoxide, was isolated from the fungal plant pathogenDrechslera gigantea. It displays unique biological activity on higher plants. On most graminaceous species, the application of 18 nanomoles to a leaf surface results in the formation of green islands — localized areas of chlorophyll retention. Gigantenone is structurally unrelated to the cytokinins, yet induces the green island effect associated with these phytohormones at comparable concentrations. However, on dicotyledonous species it generally causes necrotic lesions. On host plants ofD. gigantea, gigantenone induced lesions closely resembling those appearing in natural infections. Gigantenone also induces root formation in mung bean hypocotyls and shows a high level of activity in several plant tissue culture systems.We thank the US-National Science Foundation (Grant DMB-8607347) for partially supporting this work.     

Free amino acids of the haemolymph of the cotton leaf-worm,Spodoptera littoralis Boisduval full-grown larvae,infected with nuclear-polyhedrosis virus

Summary Free amino acids in the haemolymph ofSpodoptera littoralis full-grown larvae infected with a nuclearpolyhedrosis virus were compared with those in the haemolymph of normal insects. Amino acids were separated by 2-dimensional paper chromatography and quantified colorimetrically. Most of the amino acids in the haemolymph of diseased full-grown larvae decreased markedly in concentration but proline, lysine, aspartic acid and histidine occurred in greater concentration in the haemolymph of diseased full-grown larvae than in the haemolymph of healthy insects.     

Integrins and cardiovascular disease

Cardiovascular diseases involve abnormal cell-cell interactions leading to the development of atherosclerotic plaque, which when ruptured causes massive platelet activation and thrombus formation. Parts of a loose thrombus may detach to form an embolus, blocking circulation at a more distant point. The integrins are a family of adhesive cell receptors interacting with adhesive proteins or with counterreceptors on other cells. There is now solid evidence that the major integrin on platelets, the fibrinogen receptor α _IIb  β ₃ , has an important role in several aspects of cardiovascular diseases and that its regulated inhibition leads to a reduction in incidence and mortality due to these disorders. The development of α _IIb  β ₃ inhibitors is an important strategy of many pharmaceutical companies which foresee a large market for the treatment of acute conditions in surgery, the symptoms of chronic conditions and, it is hoped, maybe even the successful prophylaxis of these conditions. Although all the associated problems have not been solved, the undoubted improvements in patient care resulting from the first of these treatments in the clinic have stimulated further research on the role of integrins on other vascular cells in these processes and in the search for new inhibitors. Both the development of specific inhibitors and of mice with specific integrin subunit genes ablated have contributed to a better understanding of the function of integrins in development of the cardiovascular system.     

Fijiensin,the first phytotoxin fromMycosphaerella fijiensis,the causative agent of Black Sigatoka disease

Summary Fijiensin, a novel phytotoxic metabolite, was isolated from a culture of the fungusMycosphaerella fijiensis, the causal agent of Black Sigatoka disease of banana. Fijiensin is phytotoxic on various banana cultivars, but not toward non-host plants. The structure of fijiensin was determined by X-ray analysis.     

Cardenolide biosynthesis in chrysomelid beetles

Summary Labeling experiments have shown that the chrysomelid beetleChrysolina coerulans is able to biosynthesize its own defensive cardenolides from cholesterol, via a pathway involving a C₂₁ intermediate, as in plants.     

Pyrrolizidine alkaloids inDanaus plexippus L. andDanaus chrysippus L.

Summary Danaus plexippus L. andDanaus chrysippus L. have been found to store pyrrolizidine alkaloids obtained from adult food plants and it is suggested that the alkaloids contribute to the unpalatability of the butterflies to potential predators.Acknowledgment. We thank Dr.C. C. J. Culvenor for rearing some of the butterflies andJ. M. Smith for plant collection. The plants were identified by the national Herbarium, Melbourne.     

Zum Vorkommen von Maltose in vegetativen Pflanzenteilen

Summary Some older results on the occurrence of maltose in higher plants have been verified; semiquantitative estimations were made. Also maltose is detected inAconitum lycoctonum and inEquisetum arvense.     

New phytotoxic butenolides produced bySeiridium cardinale,the pathogen of cypress canker disease

Summary Two new butenolides, seiridin andiso-seiridin, were isolated from culture filtrates ofSeiridium cardinale, the pathogen of cypress canker, a destructive disease ofCupressus and relatedConiferae These metabolites were characterized as 3-methyl-4-(2-hydroxyheptyl)-2(5H)-furanone and its 4-(3-hydroxyheptyl) isomer, respectively. Chlorotic, and necrotic symptoms were produced on leaves of either host or non-host test plants by absorption of 0.3 mg/ml solutions of either compound. These also showed antibacterial activity.This study was supported in part by the National Research Council, Rome (special ad hoc project Chimica fine e secondaria) and in part by the Ministry of Education, Rome.     

Role of fungal statling growth products in inter-specific competition among phylloplane fungi

Summary The effect of fungal staling growth products on leaf-inhabiting microfungi, with special reference to a leaf spot pathogenPestalotiopsis funerea Desm. ofEucalyptus globulus Labill. was studied. Results depict that antibiotics produced by competing microfungi caused the phenomenon of mycostasis on the leaf surfaces.Acknowledgments. I would like to express my thanks to Professor R.S. Dwivedi for his encouragement and to CSIR (Indian Govt.) for financial assistance.     

Mechanisms of self-incompatibility in flowering plants

Self-incompatibility is a widespread mechanism in flowering plants that prevents inbreeding and promotes outcrossing. The self-incompatibility response is genetically controlled by one or more multi-allelic loci, and relies on a series of complex cellular interactions between the self-incompatible pollen and pistil. Although self-incompatibility functions ultimately to prevent self-fertilization, flowering plants have evolved several unique mechanisms for rejecting the self-incompatible pollen. The self-incompatibility system in the Solanaceae makes use of a multi-allelic RNase in the pistil to block incompatible pollen tube growth. In contrast, the Papaveraceae system appears to have complex cellular responses such as calcium fluxes, actin rearrangements, and programmed cell death occurring in the incompatible pollen tube. Finally, the Brassicaceae system has a receptor kinase signalling pathway activated in the pistil leading to pollen rejection. This review highlights the recent advances made towards understanding the cellular mechanisms involved in these self-incompatibility systems and discusses the striking differences between these systems. Received 10 May 2001; received after revision 20 June 2001; accepted 20 June 2001