Catching profound optical flares in blazars

Flaring episodes in blazars represent one of the most violent processes observed in extra-galactic objects. Studies of such events shed light on the energetics of the physical processes occurring in the innermost regions of blazars, which cannot otherwise be resolved by any current instruments. In this work, we present some of the largest and most rapid flares captured in the optical band in the blazars 3C 279, OJ 49, S4 0954+658, TXS 1156+295 and PG 1553+113. The source flux was observed to increase by nearly ten times within a timescale of a few weeks. We applied several methods of time series analysis and symmetry analysis. Moreover, we also performed searches for periodicity in the light curves of 3C 279, OJ 49 and PG 1553+113 using the Lomb-Scargle method and found plausible indications of quasi-periodic oscillations (QPOs). In particular, the 33- and 22-day periods found in 3C 279, i.e. a 3:2 ratio, are intriguing. These violent events might originate from magnetohydrodynamical instabilities near the base of the jets, triggered by processes modulated by the magnetic field of the accretion disc. We present a qualitative treatment as the possible explanation for the observed large amplitude flux changes in both the source-intrinsic and source-extrinsic scenarios.Comment: 11 pages, 6 figures, MNRAS accepte

Profound optical flares from the relativistic jets of active galactic nuclei

Intense outbursts in blazars are among the most extreme phenomena seen in extragalactic objects. Studying these events can offer important information about the energetic physical processes taking place within the innermost regions of blazars, which are beyond the resolution of current instruments. This work presents some of the largest and most rapid flares detected in the optical band from the sources 3C 279, OJ 49, S4 0954+658, Ton 599, and PG 1553+113, which are mostly TeV blazars. The source flux increased by nearly ten times within a few weeks, indicating the violent nature of these events. Such energetic events might originate from magnetohydrodynamical instabilities near the base of the jets, triggered by processes modulated by the magnetic field of the accretion disc. We explain the emergence of flares owing to the injection of high-energy particles by the shock wave passing along the relativistic jets. Alternatively, the flares may have also arisen due to geometrical effects related to the jets. We discuss both source-intrinsic and source-extrinsic scenarios as possible explanations for the observed large amplitude flux changes.Comment: 8 pages, 2 figures, 38th International Cosmic Ray Conference (ICRC2023) proceeding

Reactive oxygen species in allelopathic interactions between plants

Allelopatia dotyczy oddziaływań pomiędzy roślinami za pośrednictwem związków chemicznych wydzielanych do środowiska. Efekty działania związków allelopatycznych w roślinach są najczęściej negatywne (zahamowanie kiełkowania nasion, ograniczenie wzrostu korzeni i/lub pędu), szczególnie gdy toksyny występują w wysokich stężeniach. Niekiedy obserwuje się też zjawisko hormezy (stymulacji kiełkowania nasion lub wzrostu organów), gdy zawartość allelozwiązków w otoczeniu jest bardzo niska. Obecność allelozwiązków wielokrotnie wywołuje w roślinach stres oksydacyjny, manifestujący się wzrostem stężenia reaktywnych form tlenu (ROS). Nie zawsze wzrost stężenia ROS w roślinach traktowanych związkami allelopatycznymi jest skorelowany ze wzrostem aktywności systemu oksydacyjnego, chociaż w ogromnej większości przypadków obserwowane są istotne zmiany aktywności podstawowych enzymów modulujących stężenie ROS (katalazy, dysmutazy ponadtlenkowej czy enzymów cyklu Halliwella-Asady), czemu towarzyszą też modyfikacje zawartości przeciwutleniaczy drobnocząsteczkowych (glutationu i askorbinianu). Z uwagi na różnorodną naturę, różne stężenia stosowanych allelozwiązków i różną wrażliwość roślin trudno jest jednoznacznie wyrokować, że zawsze i każdy związek allelopatyczny indukuje stres oksydacyjny, chociaż taka możliwość jest prawdopodobna i często spotykana. W pracy przedstawiono szereg przykładów indukcji stresu oksydacyjnego w roślinach poddanych działaniu związków allelopatycznych. Nagromadzanie ROS w komórkach i modyfikacje wzrostu roślin akceptorowych w odpowiedzi na allelozwiązki zostały porównane z tzw. reakcją SIMR (ang. stress induced morphogenic response), a także skorelowane z modyfikacją równowagi hormonalnej i czynnikami wpływającymi na strukturę ścian komórkowych. Podjęto także problem zależności pomiędzy oddziaływaniami allelopatycznymi a wrażliwością roślin na inne stresy biotyczne i abiotyczne.Allelopathy phenomenon describes mostly negative interactions between plants mediated by specific chemicals released into environment. Inhibition of growth of various organs, and delay or restriction of seed germination are most frequently observed effects of allelopathic interactions. At times, allelochemicals subjected in low concentration may also lead to hormesis (stimulation of seed germination or plant growth). Allelochemicals often induce oxidative stress, manifested as an increase in ROS production, which not always correlates with enhancement of cellular antioxidant systems, although in most cases there are observed significant changes in the activity of ROS modulating enzymes: catalase, superoxide dismutase and enzymes of Halliwell-Asada cycle, accompanied by modification in the level of low molecular antioxidants ascorbate and glutathione. In view of large differences in plant sensitivity to allelochemicals, and a wide range of concentration of already tested compounds, it is hardly to believe that induction of oxidative stress is an uniform response to allelopathy stress. In this work, there are described selected examples of various allelochamicals or extracts from allelopathic plants known to induce oxidative stress in acceptor organisms. Accumulation of ROS and modification of growth and/or development of organs of acceptor plants induced by allelochemicals are correlated with "stress induced morphogenic response" (SIMR), modification of phytohormonal balance and factors crucial for cell wall formation. Additionally, the relationship between allelopathic interaction and plant sensitivity to other biotic and abiotic stresses is discussed

ROS Metabolism Perturbation as an Element of Mode of Action of Allelochemicals

The allelopathic interaction between plants is one of the elements that influences plant communities. It has been commonly studied by applying tissue extracts onto the acceptors or by treating them with isolated allelotoxins. Despite descriptive observations useful for agricultural practice, data describing the molecular mode of action of allelotoxins cannot be found. Due to the development of -omic techniques, we have an opportunity to investigate specific reactive oxygen species (ROS)-dependent changes in proteome or transcriptome that are induced by allelochemicals. The aim of our review is to summarize data on the ROS-induced modification in acceptor plants in response to allelopathic plants or isolated allelochemicals. We present the idea of how ROS are involved in the hormesis and plant autotoxicity phenomena. As an example of an -omic approach in studies of the mode of action of allelopatic compounds, we describe the influence of meta-tyrosine, an allelochemical exudated from roots of fescues, on nitration—one of nitro-oxidative posttranslational protein modification in the roots of tomato plants. We conclude that ROS overproduction and an induction of oxidative stress are general plants’ responses to various allelochemicals, thus modification in ROS metabolisms is regarded as an indirect mode of action of allelochemicals

Canavanine Increases the Content of Phenolic Compounds in Tomato (Solanum lycopersicum L.) Roots

Canavanine (CAN) is a nonproteinogenic amino acid, and its toxicity comes from its utilization instead of arginine in many cellular processes. As presented in previous experiments, supplementation of tomato (Solanum lycopersicum L.) with CAN led to decreased nitric oxide (NO) level and induced secondary oxidative stress. CAN improved total antioxidant capacity in roots, with parallel inhibition of enzymatic antioxidants. The aim of this work was to determine how CAN-dependent limitation of NO emission and reactive oxygen species overproduction impact content, localization, and metabolism of phenolic compounds (PCs) in tomato roots. Tomato seedlings were fed with CAN (10 and 50 µM) for 24 or 72 h. Inhibition of root growth due to CAN supplementation correlated with increased concentration of total PCs; CAN (50 µM) led to the homogeneous accumulation of PCs all over the roots. CAN increased also flavonoids content in root tips. The activity of polyphenol oxidases and phenylalanine ammonia-lyase increased only after prolonged treatment with 50 µM CAN, while expressions of genes encoding these enzymes were modified variously, irrespectively of CAN dosage and duration of the culture. PCs act as the important elements of the cellular antioxidant system under oxidative stress induced by CAN

Toxicity of meta-Tyrosine

L-Tyrosine (Tyr) is one of the twenty proteinogenic amino acids and also acts as a precursor for secondary metabolites. Tyr is prone to modifications, especially under conditions of cellular redox imbalance. The oxidation of Tyr precursor phenylalanine leads to the formation of Tyr non-proteinogenic isomers, including meta-Tyr (m-Tyr), a marker of oxidative stress. The aim of this review is to summarize the current knowledge on m-Tyr toxicity. The direct m-Tyr mode of action is linked to its incorporation into proteins, resulting in their improper conformation. Furthermore, m-Tyr produced by some plants as an allelochemical impacts the growth and development of neighboring organisms. In plants, the direct harmful effect of m-Tyr is due to its modification of the proteins structure, whereas its indirect action is linked to the disruption of reactive oxygen and nitrogen species metabolism. In humans, the elevated concentration of m-Tyr is characteristic of various diseases and ageing. Indeed, m-Tyr is believed to play an important role in cancer physiology. Thus, since, in animal cells, m-Tyr is formed directly in response to oxidative stress, whereas, in plants, m-Tyr is also synthesized enzymatically and serves as a chemical weapon in plant–plant competition, the general concept of m-Tyr role in living organisms should be specified

ROS and RNS Alterations in the Digestive Fluid of <i>Nepenthes</i> × <i>ventrata</i> Trap at Different Developmental Stages

The carnivorous pitcher plant, Nepenthes × ventrata (Hort. ex Fleming = N. ventricosa Blanco × N. alata Blanco), produces passive traps containing digestive fluid. Although reactive oxygen species (ROS) in the fluid were detected in some pitcher plants, the participation of reactive nitrogen species (RNS) in the digestion process has not yet been examined. The aim of this work was to investigate the production of superoxide anion (O2•−), nitric oxide (NO) and peroxynitrite (ONOO−) levels in the digestive fluid of traps throughout organ development. We revealed the ROS and RNS occurrence in the digestive fluid, linked to the ROS-scavenging capacity and total phenolics content. In digestive fluid from the fed traps, NO emission was higher than in the fluid from the developed unfed pitcher. The concentration of nitrite (NO2−) decreased in the fluid from the fed traps in comparison to the unfed ones, pointing at NO2− as the key source of NO. The enhanced emission of NO was associated with lowered content of ONOO− in the fluid, probably due to lower production of O2•−. At the same time, despite a decline in total phenolics, the maximum ROS scavenging capacity was detected. In addition, ROS and RNS were noted even in closed traps, suggesting their involvement not only in digestion per se but also their action as signaling agents in trap ontogeny

Is the Phytotoxic Effect of Digestive Fluid of <i>Nepenthes x ventrata</i> on Tomato Related to Reactive Oxygen Species?

The digestive fluid of pitcher plants is a rich source of enzymes and secondary metabolites, but its impact on higher plant growth and development remains unknown. The aim of the study was to determine the phytotoxicity of the digestive fluid of the pitcher plant (Nepenthes x ventrata) on the germination of tomato (Solanum lycopersicum L.) seeds, elongation growth and cell viability of roots of tomato seedlings. The digestive fluid was collected from pitchers before feeding and four days after feeding; the pH and electrical conductivity of the fluid were determined. Undiluted and 50% fluids were used in the study. An inhibition of germination of tomato seeds, by around 30% and 55%, was respectively observed in 50% and 100% digestive fluids collected before and after feeding. Digestive fluid did not affect the root growth of tomato seedlings; a slight (6%) inhibition was only observed after the application of 100% digestive fluid from an unfed trap. The roots of the tomato seedlings treated with undiluted fluid were characterized by reduced cell viability. Reactive oxygen species (H2O2 and O2•−) were mainly localized in the root apex regardless of the used phytotoxic cocktail, and did not differ in comparison to control plants

Nitric Oxide in Seed Biology

Nitric oxide (NO) has been recognized as a gasotransmitter in the mainstream of plant research since the beginning of the 21st century. It is produced in plant tissue and the environment. It influences plant physiology during every ontogenetic stage from seed germination to plant senescence. In this review, we demonstrate the increased interest in NO as a regulatory molecule in combination with other signalling molecules and phytohormones in the information network of plant cells. This work is a summary of the current knowledge on NO action in seeds, starting from seed pretreatment techniques applied to increase seed quality. We describe mode of action of NO in the regulation of seed dormancy, germination, and aging. During each stage of seed physiology, NO appears to act as a key agent with a predominantly beneficial effect