Rośliny narażone są na różnorodne biotyczne i abiotyczne czynniki stresowe, które mogą powodować zranienie organizmu roślinnego. Odpowiedź rośliny na uszkodzenie mechaniczne może mieć charakter lokalny i/lub systemowy i obejmuje m. in. transdukcję sygnału o zranieniu, która prowadzi do ekspresji wielu różnych genów. W odpowiedzi roślin na zranienie główną rolę odgrywa kwas jasmonowy i jego pochodne. Ważną rolę przypisuje się również innym związkom chemicznym, takim jak: oligopeptyd systemina, oligosacharydy, lotne związki organiczne oraz fitohormony (np. kwas abscysynowy). W odpowiedzi na zranienie biorą również udział czynniki fizyczne, takie jak: fala hydrauliczna, czy impulsy elektryczne. Wymienione komponenty szlaków sygnałowych są kontrolowane i regulowane przez interakcje z innymi wewnątrzkomórkowymi kaskadami sygnałowymi u roślin, do których należy: odwracalna fosforylacja białek, zmiany wewnątrzkomórkowego stężenia jonów wapnia, regulowane przez kalmodulinę oraz produkcja reaktywnych form tlenu, takich jak anionorodnik ponadtlenkowy i nadtlenek wodoru. Niektóre substancje chemiczne zaangażowane w transdukcję sygnału o zranieniu funkcjonują również w szlakach sygnałowych jako rezultat działania czynników stresowych, innych niż uszkodzenie mechaniczne, np. w reakcji na infekcję przez patogeny. Zrozumienie mechanizmów, które są odpowiedzialne za reakcje na zranienie, zarówno w obrębie organizmu roślinnego jak i w kontekście oddziaływania roślina - środowisko, ma istotne znaczenie poznawcze i może mieć zastosowanie praktyczne, zwłaszcza w szeroko pojętej ochronie roślin.
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Plants during life are exposed to different abiotic and biotic stress factors. Both of them can induce wounding of a plant body. Responses to mechanical damage are local or/and systemic and hence involve the transduction of wound signals to activate the expression of various genes. In plant responses to wounding the central role plays jasmonic acid and its derivatives, but other compounds, including the oligopeptide systemin, oligosaccharides, volatile organic compounds and phytohormones e. g. abscisic acid are also important. Additionally, physical factors such as hydraulic pressure or electrical pulses, have also been proposed as a crucial factors involved in wound signaling. These components of signaling pathways are controlled in time and space by highly complex regulatory networks modulated by interactions with other signaling cascades in plants. They include reversible protein phosphorylation steps, calcium calmodulin-regulated events, and production of reactive oxygen species such as superoxide anion radical and hydrogen peroxide. Indeed, some of these components involved in transducing of wound signals also function in signaling of other plant defence responses, mainly in pathogen responses, suggesting that cross-talk events may regulate temporal and spatial activation of different defences. Understanding the ways in which wound signaling pathways are coordinated individually and in the context of the plants environment is crucial in the application of this knowledge to plants crop protection strategies.
The redox status of the cell is described by the ratio of reduced to non-reduced compounds. Redox reactions which determine the redox state are an essential feature of all living beings on Earth. However, the first life forms evolved under strongly anoxic conditions of the young Earth, and the redox status probably was based on iron and sulphur compounds. Nowadays, redox reactions in cells have developed in strict connection to molecular oxygen and its derivatives i.e. reactive oxygen species (ROS). Oxygen has started to accumulate on the Earth due to oxygenic photosynthesis. All aspects of aerobic life involve ROS, reactive nitrogen species (RNS), antioxidants and redox regulation. Many different redox-active compounds are involved in the complex of redox processes, including pyridine nucleotides, thioredoxins, glutaredoxins and other thiol/disulphide-containing proteins. Redox regulation is integrated with the redox-reactions in photosynthesis and respiration to achieve an overall energy balance and to maintain a reduced state necessary for the biosynthetic pathways that are reductive in nature. It underlies the physiological and developmental flexibility in plant response to environmental signals.
Hydrogen peroxide (H2O2) is produced predominantly in plant cells during photosynthesis and photorespiration, and to a lesser extent, in respiration processes. It is the most stable of the so-called reactive oxygen species (ROS), and therefore plays a crucial role as a signalling molecule in various physiological processes. Intra- and intercellular levels of H2O2 increase during environmental stresses. Hydrogen peroxide interacts with thiol-containing proteins and activates different signalling pathways as well as transcription factors, which in turn regulate gene expression and cell-cycle processes. Genetic systems controlling cellular redox homeostasis and H2O2 signalling are discussed. In addition to photosynthetic and respiratory metabolism, the extracellular matrix (ECM) plays an important role in the generation of H2O2, which regulates plant growth, development, acclimatory and defence responses. During various environmental stresses the highest levels of H2O2 are observed in the leaf veins. Most of our knowledge about H2O2 in plants has been obtained from obligate C3 plants. The potential role of H2O2 in the photosynthetic mode of carbon assimilation, such as C4 metabolism and CAM (Crassulacean acid metabolism) is discussed. We speculate that early in the evolution of oxygenic photosynthesis on Earth, H2O2 could have been involved in the evolution of modern photosystem II.
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