The production of different morphs by alate viviparae of the aphid Myzus persicae temporarily exposed to long scotophases

The development of alatae of the green peach aphid, Myzus persicae, as gynoparae rather than as virginoparae was investigated with regard to the number of exposures to a long-night (LN) regime of 15 h darkness per diem which the aphids experienced before and/or after their birth. The minimum number of exposures to LN that resulted in all of the alatae developing into gynoparae was two prenatal plus one postnatal or one prenatal plus two postnatal, provided the scotophases in these treatments were at least 12 h long. A cumulative effect of several successive exposures to LN was also evident when the presumptive alatae were exposed to LN either from birth or not until several days after birth. Fewer exposures to LN were needed in the former case.

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Zusammenfassung Die Entwicklung von Alatae der grünen Pfirsichblattlaus, Myzus persicae, hauptsächlich zu Gynoparae, eher als zu Virginoparae, wurde im Hinblick auf den Einfluss der Anzahl an Langnächten (LN: 15 Studen Dunkelheit pro Tag), denen die Aphiden vor und/oder nach der Geburt ausgesetzt waren, untersucht. Zur ausschliesslichen Entwicklung aller Alatae zu Gynoparae waren mindestens 2 prenatale und eine postnatale LN-Exposition oder eine prenatale und 2 postnatale LN-Expositionen notwendig, vorausgesetzt die Dunkelphasen betrugen mindestens 12 Stunden. Ausserdem zeigte sich ein kumulativer Effect durch mehrere, aufeinanderfolgende LN-Expositionen, wenn die Alatae diesen von Geburt an, oder einige Tage nach der Geburt, ausgesetzt waren. Im ersten Fall waren weniger LN-Expositionen notwendig.

     

Oxidative stress responses and shock proteins in the unicellular cyanobacterium Synechococcus R2 (PCC-7942)

Oxidative stress responses were tested in the unicellular cyanobacterium Synechococcus PCC 7942 (R2). Cells were exposed to hydrogen peroxide, cumene hydroperoxide and high light intensities. Activities of ascorbate peroxidase and catalase were correlated with the extent and time-course of oxidative stresses. Ascorbate peroxidase was found to be the major enzyme involved in the removal of hydrogen peroxide under the tested oxidative stresses. Catalase activity was inhibited in cells treated with high H₂O₂ concentrations, and was not induced under photo-oxidative stress. Regeneration of ascorbate in peroxide-treated cells was found to involve mainly monodehydroascorbate reductase and to a lesser extent dehydroascorbate reductase. The induction of the antioxidative enzymes was dependent on light and was inhibited by chloramphenicol. Peroxide treatment was found to induce the synthesis of eight proteins, four of which were also induced by heat shock.Abbreviations ASC ascorbate - DHA dehydroascorbate - MDA monodehydroascorbate - GSH reduced glutathione - GSSG oxidized glutathione - ASC Per ascorbate peroxidase - DHA red. dehydroascorbate reductase - MDA red. monodehydroascorbate reductase - GSSG red. glutathione reductase - HSP heat shock proteins - PSP peroxide shock proteins - C_m chloramphenicol     

Precocene causes male determination in the aphid Myzus persicae

When adult apterous viviparous females of Myzus persicae, reared in short night conditions at 21–23°C, are treated with the precocene analogue 6-methoxy-7-ethoxy-2,2-dimethylchromene, they deposit males towards the end of their reproductive lives. The first-born normal daughters of the treated females also deposit some males at various times in their reproductive lives. Karyotypic analysis was used to investigate the sequence of male and female embryos in the ovarioles of precociously metamorphosed aphids. The experiments support the hypothesis (Mittler et al., 1979) that juvenile hormone level controls the sex determination process in aphids. Since male aphids have an XO sex chromosome constitution, this implies that juvenile hormone level influences the behaviour of the X-chromosomes at or before the single maturation division of the egg. At this division one X-chromosome is eliminated from eggs which will develop as males. Aphids provide the first example of a specific endocrine influence on chromosome behaviour in sex determination.     

Oesophageal and stomach inclusions of aphids feeding on various cruciferae

When Myzus persicae, and a few other aphid species tested, feed on broad leaf mustard (Brassica juncea) or on one of several other Cruciferae, there regularly occur in their stomachs rod-or sausage-like structures with a diameter of about 5–15 µ. On other host plants, in particular on Solanaceae and Chenopodiaceae, or on tulip and on an artificial diet, these structures do not occur. The material passes through the oesophagus into the stomach and accumulates there throughout the life of an aphid. The material is stainable with neutral red. In killed aphids the material gradually darkens. The material already begins to appear in some individuals one hour after transferring them from noncruciferous host plants or from the diet to mustard. In the lumen of the oesophagus the material may occur as short or long fragments, or as a strand extending through its entire length. The oesophagus is cleared of this material in nearly all aphids within 4 hours of feeding on tulip and within about 24 hours on an artificial diet, whereas this occurs in only half the aphids within a 24-hour period of starvation. It is assumed that the material consists of swallowed saliva which has been changed by the cruciferous sap.

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Feste partikel in oesophagus und magen bei aphiden an cruciferen

Zusammenfassung Wenn Myzus persicae (Sulzer) und andere Aphidenarten an broad leaf mustard (Brassica juncea Coss., Rutensenf) und an einigen anderen Cruciferen saugen, finden sich im Magen regelmäßig stäbchen- oder würstchenförmige oder auch klumpige, feste Partikel mit einem Durchmesser von etwa 5–15 und mehr µ vor. Diese lassen leicht mit Neutralrot färben, sind in 1 N HCl auch in der Hitze beständig und färben sich in getöteten Tieren von selbst braun oder schwarz. In Läusen, die an anderen Wirtspflanzen, insbesondere an Solanaceen und Chenopodiaceen, an Tulpe oder an einer künstlichen Diät aufwuchsen, fehlen diese Partikel.Das Material gelangt durch den ösophagus in den Magen, wo es sich während des ganzen Lebens ansammelt. Im Lumen des Ösophagus kann es in Form kürzerer oder längerer Stücke oder als langer Strang vorliegen, der vom Cibarium durch den Ösophagus und das Magenventil in den Magen reicht und diesen in mehrfachen Windungen durchzieht. Bei Übertragung von Nichtcruciferen auf broad leaf mustard erscheint das Material manchmal schon nach einstündigem, meist erst nach 2–6 stündigem Saugen oder später. Die Aufnahme des Materials erfolgt nicht oder zum mindesten nicht bevorzugt während des Einstichvorganges. Es wird diskutiert, ob es sich um aufgenommenen Speichel, der durch eine Pflanzensaftkomponente verändert ist, handelt.Im Magen von vielen Blattlausarten finden sich bei adulten Tieren vier fädige, an einem Ende angeschwollene Gebilde (bei Larven entsprechend weniger), die als die Intima von Ösophagus und Valvula cardiaca identifiziert wurden. Sie müssen nach den Häutungen in den Magen gelangen und hier verbleiben (abb. 2).

     

Coordinated Activation of Programmed Cell Death and Defense Mechanisms in Transgenic Tobacco Plants Expressing a Bacterial Proton Pump

In plants, programmed cell death is thought to be activated during the hypersensitive response to certain avirulent pathogens and in the course of several differentiation processes. We describe a transgenic model system that mimics the activation of programmed cell death in higher plants. In this system, expression of a bacterial proton pump in transgenic tobacco plants activates a cell death pathway that may be similar to that triggered by recognition of an incompatible pathogen. Thus, spontaneous lesions that resemble hypersensitive response lesions are formed, multiple defense mechanisms are apparently activated, and systemic resistance is induced in the absence of a pathogen. Interestingly, mutation of a single amino acid in the putative channel of this proton pump renders it inactive with respect to lesion formation and induction of resistance to pathogen challenge. This transgenic model system may provide insights into the mechanisms involved in mediating cell death in higher plants. In addition, it may also be used as a general agronomic tool to enhance disease protection.     

In Situ Detection of nDNA Fragmentation during the Differentiation of Tracheary Elements in Higher Plants

Programmed cell death (pcd) is thought to occur during the autolysis of xylem vessels. Although several ultrastructural aspects of this differentiation process have been characterized, certain key aspects of this process remain unsolved. Here we demonstrate in pea (Pisum sativum) that nuclei of vessel elements undergoing pcd contain fragmented nDNA. This finding may provide evidence for the activation of a DNA degradation mechanism prior to the final disruption of the nucleus that occurs during the autolysis stage of this differentiation process. In situ detection of DNA fragmentation in nuclei of vessel elements undergoing pcd may therefore suggest that this death process involves the activation of a mechanism for DNA degradation, similar to that activated during apoptosis in animal cells. In addition, this differentiation process may serve as a useful positive control for the in situ detection of pcd in other developmental pathways and during the hypersensitive response of plants to avirulent pathogens.     

INFLUENCE OF DAYLENGTH ON THE PRODUCTION OF PARTHENOGENETIC AND SEXUAL FEMALES OF APHIS FABAE AT 17.5°

When apterous virginoparae of Aphis fabae and their progenies were raised at 17.5^o on leaf discs of Vicia faba under photoperiods of 12 h or less per day, more alatae occurred among the progenies than under longer photoperiods. The alatae developed exclusively into gynoparae at 4, 10 and 12 h light per day and almost all did so at 2 h. At 13 h 45 min, 14 h, 16 h, and 24 h all the alatae developed into virginoparae. At transitional photoperiods ranging from 13 h 6 min to 13 h 28 min, both alate morphs occurred. They could both be deposited by a single apterous virginopara and produce intermorphs containing eggs and embryos. Under most light regimes, a proportion of the gynoparae (generally < 10%) produced some apterous virginoparae, gynoparae, and males after producing a number of oviparae. Alate virginoparae produced almost three times as many larvae as did the gynoparae.By transferring alatiform larvae produced by apterae raised at short day (SD: 10 h light) to long day (LD: 16 h light) or vice versa, a strong prenatal influence of SD on gynopara production was demonstrated. SD also had a postnatal influence on presumptive virginoparous alatiforms, if they were transferred to SD already in the 1 st instar. Alatiform larvae could be influenced by SD or LD as late as in the 3d instar if they and their mothers had been maintained under a weak short (13 h 6 min) or a weak long day (13 h 45 min).The results are discussed in relation to possible hormonal mechanisms of morph determination.

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Zusammenfassung Wenn ungeflügelte, virginopare Aphis fabae und ihre Nachkommen gehalten wurden bei 17,5^o auf Blattscheiben von Vicia faba bei Fotoperioden von 12 oder weniger Stunden je Tag, so entstanden mehr Geflügelte unter den Nachkommen als unter längeren Fotoperioden. Die Geflügelten entwickelten sich ausschliesslich zu Gynoparen bei 4, 10 und 12 h Licht je Tag und fast alle bei 2 h. Bei 13 h 45 min, 14, 16 und 24 h entwickelten sich alle Geflügelten zu Virginoparen. Bei Übergangsfotoperioden zwischen 13 h 6 min und 13 h 28 min kamen beide geflügelte Morphen vor. Diese konnten beide von einer einzigen ungeflügelten Virginopara abgesetzt werden und Zwischenformen mit Eiern und Embryonen erzeugen. Bei den meisten Fotoperioden erzeugte ein Teil der Gynoparen (meist < 10%) einige ungeflügelte Virginopare, Gynopare und Männchen, nachdem sie eine Anzahl von Oviparen erzeugt hatten. Geflügelte Virginopare erzeugten fast dreimal so viele Larven als wie Gynopare es tun.Wenn man alatiforme Larven, deren ungeflügelte Mütter bei Kurztag (KT: 10 h Licht) gehalten waren, in Langtag (LT: 16 h Licht) übertrug oder umgekehrt, so zeigte sich ein starker pränataler Einfluss des KT auf die Gynoparenerzeugung. KT hatte auch einen postnatalen Einfluss auf präsumptive virginopare geflügelte Formen, wenn diese schon im 1. Larvenstadium übertragen wurden. Alatiforme Larven konnten selbst noch im 3. Stadium durch KT oder LT beeinflusst werden, wenn sie und ihre Mütter bei schwachem Kurz- (13 h 6 min) oder schwachem Lang- (13 h 45 min) Tag gehalten waren.Die Ergebnisse werden in Hinsicht auf mögliche hormonale Mechanismen der Morphenbestimmung diskutiert.

     

Macrophage factor controlling differentiation of B cells.

Peritoneal macrophages of the mouse produce, in response to cell wall components of Gram-negative bacteria (lipopolysaccharide and lipoproteins), a factor that causes antigen-stimulated B cells of differentiate into antibody-producing cells. Unlike lipopolysaccharide, this factor is not mitogenic for B cells. Production of the macrophage factor does not depend on participation of T cells or other accessory cells since it is readily produced by several cloned macrophage cell lines as well as by peritoneal macrophages of athymic nude mice. The factor is active only in conjunction with antigen. T cells, although apparently not necessary, amplify its effect. The factor induces phenotypic differentiation of B cell precursors as selectively as thymopoietin induces differentiation of prothymocytes.