A planar microtubule-organizing zone in guard cells of Allium: experimental depolymerization and reassembly of microtubules

The generation of the unique radial array of microtubules (MTs) in stomatal guard cells raises questions about the location and activities of relevant MT-organizing centers. By using tubulin immunofluorescence microscopy, we studied the pattern of depolymerization and reassembly of MTs in guard cells of Allium cepa L. Chilling at 0°C reduces the MTs to small remnants that surround the nuclear surface of cells in the early postcytokinetic stage, or form a dense layer along the central portion of the ventral wall in older guard cells. A rapid reassembly on rewarming restores either MTs extending from the nuclear surface randomly throughout the cytoplasm in very young cells, or an array of MTs radiating from the dense layer at the ventral wall later in development. A similar pattern of depolymerization and reassembly is achieved by incubation with 100 M colchicine followed by a brief irradiation with ultraviolet (UV) light. Incubation with 200 M colchicine leads to a complete depolymerization that leaves only a uniform, diffuse cytoplasmic fluorescence. Nonetheless, UV irradiation of developing guard cells induces the regeneration of a dense layer of MTs at the ventral wall. The layer is again positioned centrally along the wall, even if the nucleus has been displaced by centrifugation in the presence of cytochalasin D. Neither the regenerated layer nor the perinuclear MTs seen earlier are related to the staining pattern of serum 5051, which reportedly binds to centrosomal material in animal and plant cells. The results support the view that, soon after cytokinesis, a planar MT-organizing zone is established in the cortex along the central portion of the ventral wall, which then generates the radial MT array.Abbreviations GC guard cell - MT microtubule - MTOC microtubule-organizing center - UV ultraviolet To whom correspondence should be addressed.     

Significance of myocardial eicosanoid production

Summary The precise role of eicosanoids in the development of myocardial injury during ischemia and reperfusion is still a matter of debate. Enhanced local production of these bioactive compounds appears to be a common response to tissue injury. Most likely, the cardiac tissue has the capacity to generate prostaglandins, thromboxanes as well as leukotrienes. Prostacyclin (PGI,) is the major eicosanoid produced by the jeopardized myocardium. In addition, at sites of tissue injury activation of platelets and infiltrating leukocytes results in the formation of considerable amounts of thromboxanes and leukotrienes. The production of eicosanoids requires prior release of arachidonic acid (AA) from phospholipids. Both ischemia and reperfusion are associated with a rise in the tissue level of AA. The absence of a proportional relationship between the tissue level of AA and the amounts of PGI, produced suggests that the sites of AA accumulation and PGI₂ formation are different. It is conceivable that AA accumulation is mainly confined to myocytes, whereas the capacity to synthesize PGI, mainly resides in vascular cells. Both beneficial and detrimental effects of eicosanoids on cardiac tissue have been described. Prostaglandins act as vasodilators. Besides, some of the prostaglandins, especially PGI,, are thought to possess cyto-protective properties. Thromboxanes and leukotrienes may impede blood supply by increasing smooth muscle tone. Besides, leukotrienes augment vascular permeability. Experimental studies, designed to evaluate the effect of pharmacological agents, like PGI₂-analogues and lipoxygenase and cyclo-oxygenase inhibitors, indicat that eicosanoids influence the outcome of myocardial injury. However, the delineation of the physiological significance of the locally produced eicosanoids is complicated by such factors as the wide variety of AA derivatives produced and the dose-dependency of their effects.     

The protein kinases tightly bound to DNA are present in normal tissues and in regenerating liver, but strongly decreased in hepatomas

We have previously described in rat liver two protein kinases tightly bound to DNA, one is serine-specific, the other arginine-specific. In this work we show that both enzymes are present in various rat tissues and in liver from various species. Both kinase specific activities are strongly decreased in methyl-DBA-induced hepatomas and in HTC cells but not in regenerating liver after hepatectomy. This decrease is then not related to cell proliferation.     

Interaction of allosteric effectors (ATP,CO2, H+) modulating oxygen affinity of the hemoglobin in the carp,Cyprinus carpio,in vitro

Summary The interaction of allosteric effectors (CO₂, ATP, H⁺) with respect to the oxygen affinity of carp hemoglobin was analyzed by determining oxygen binding curves spectrophotometrically in dilute solutions of stripped hemoglobin at 20°C. The pH range studied was 6.8–8.2.P _CO2 was 0, 10 and 70 mmHg (0, 1.33 and 9.3 kPa). ATP/Hb₄ was 0, 8 and 24. In the presence of either CO₂ or ATP, the effects of the cofactors onP ₅₀ were as expected over the whole pH range. In contrast to other published data, each cofactor also had a significant effect onP ₅₀ in the presence of the other cofactor. Evidence was obtained that oxylabile carbamate is formed by carp hemoglobin and that the formation of carbamate persists at a lower level in the presence of ATP. The results support the view that the binding of ATP to carp hemoglobin requires only one terminal amino group, leaving the other N-terminal of the -chain free to react with CO₂.     

Use of pheromone chemistry to identify Grapholita lobarzewskii as an occasional pest of apple and plum

As shown by chemical analysis and field trapping, the sex pheromone of Grapholita lobarzewskii consists of a blend of (E)-8-dodecenyl acetate and (Z)-8-dodecenyl acetate. Maximum attractiveness was found at 80–95%. Dodecyl acetate and tetradecyl acetate, both present in the female gland, did not affect trap catch. G. lobarzewskii has recently gained importance as a pest of apple and plum, but has so far been referred to as Grapholita janthinana. The latter is attracted to the same two compounds, but in reversed portions (20% E).

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Zusammenfassung Chemische Analysen und Feldversuche zeigen, dass das Sexualpheromon des Kleinen Fruchtwicklers, G. lobarzewskii aus (E)-8-Dodecenylacetat (Z8-12:Ac) und (Z)-8-Dodecenylacetat (Z8-12:Ac) besteht. Die grösste Lockwirkung wurde mit einem Gemisch der beiden Substanzen bei einem E-Anteil von 80–95% erzielt. Dodecylacetat (12:Ac) und Tetradecylacetat (14:Ac) wurden ebenfalls in den weiblichen Pheromondrüsen nachgewiesen, hatten aber im Freiland keinen Einfluss auf die Lockwirkung. G. lobarzewskii tritt seit einiger Zeit in der Schweiz als Schädling von Apfel und Zwetschge auf und ist an ihrem charakteristischem Frassgang leicht erkennbar. Die Art wurde bisher irrtümlich als G. janthinana bezeichnet. G. janthinana lebt auf Rosaceen, und wird vom gleichen Substanzpaar angelockt, allerdings bei umgekehrtem Mischungsverhältnis (20% E).

     

Extracellular ATP stimulates poly(inositol phospholipid) hydrolysis and eicosanoid synthesis in mouse peritoneal macrophages in culture

The effects of extracellular ATP on inositol phospholipid breakdown and synthesis of eicosanoids were studied in mouse peritoneal macrophages. Addition of ATP to intact cells labelled with [3H]inositol stimulated a rapid (within 10 s) formation of inositol 1,4,5-trisphosphate and inositol 1,3,4,5-tetrakisphosphate. In parallel there was also a substantial accumulation of inositol 1,3,4-trisphosphate and the monophosphate and bisphosphate derivatives of inositol. Within 10 s after the addition of 30 microM ATP there was a twofold increase in inositol trisphosphate (InsP3), which declined over 2 min. The ED50 for ATP-stimulated generation of InsP3 was approximately 12 microM. ADP and GTP showed only weak effects on InsP3 formation, while AMP and adenosine were completely ineffective at 30 microM. Furthermore, the rank order of potency of ATP analogues was ATP greater than ATP[S] greater than AdoPP[NH]P = AdoPP[CH2]P greater than AdoP[CH2]PP thus, indicating the presence of a P2y-purinergic receptor. Cells labelled with [3H]arachidonic acid showed a 50% increase of label in 1,2-diacylglycerol after 15 s upon stimulation with ATP. In parallel to the stimulation of inositol phospholipid hydrolysis, ATP also caused a marked synthesis of prostaglandin E2 (PGE2) and leukotriene C4 (LTC4) in mouse peritoneal macrophages. The rank order of potency of ATP analogues was identical with that of InsP3 generation. The effect on eicosanoid synthesis could be mimicked by the calcium ionophore A23187 and the phorbol ester 12-O-tetradecanoylphorbol 13-acetate. These results suggest that ATP-induced activation of P2y-purinergic receptors in mouse peritoneal macrophages triggers inositol phospholipid breakdown and eicosanoid synthesis.     

Evidence for a novel growth factor in Xenopus oocytes

Xenopus oocytes contain a novel growth factor, as determined by its effect on the anchorage-dependent and -independent growth of various rat cells and on a Xenopus cell line; it is destroyed by trypsin, acidification (pH 2.0), heating (100 degrees C, 3 min), 8 M urea but not by dithiothreitol. Gel filtration of this activity in nondissociating conditions suggests the existence of aggregates and the presence of a very high (approximately 2000 Kd) and a much lower (approximately 30 Kd) form.     

Chlamydosporol,a new metabolite from Fusarium chlamydosporum

Extracts of rice on which an isolate of Fusarium chlamydosporum had been cultured were toxic to brine shrimps. The toxic fraction was purified by flash chromatography to give two compounds which were identified by UV, IR, NMR and mass spectroscopy at the 6 and 6 isomers of 5-hydroxy-4-methoxy-6, 8a-dimethyl-6,7-dihydro-2H,8aH-pyrano[2,3-b]pyran-2-one. These lactones for which the name chlamydosporol is proposed have not been reported previously. When tested in brine shrimp and HeLa cell assays, the LC₅₀ concentration for a mixture of the isomers was approximately 400 g/ml in both systems.     

On the evolutionary ecology of marking pheromones

Summary Many parasitic insects mark hosts with a pheromone after oviposition. The evolutionary ecology of such marking pheromones was studied to determine (i) under what ecological and behavioral conditions such pheromones could evolve and (ii) why so many of these marking pheromones are water-soluble and thus short-lived. We used a number of different techniques. First, the fitness values of individual normal (nonmarking) and mutant (marking) insects foraging for hosts were computed using dynamic state-variable models. Second, population level models were used to study when a population of non-marking individuals can be invaded by marking individuals. Third, behavior-rich simulations (developed originally for apple maggot,Rhagoletis pomonella) were used to test experimentally some of the hypotheses generated using the individual and population-level models. Finally, we developed a model for the benefit over time to an individual by marking. This model shows that when benefit is measured in terms of larval survival, nearly all of the benefit to a mother is obtained from short-lived marks. Genetical theories of pheromone evolution and the connection between our results and existing theories of altruistic behavior are discussed.