Browsing by Subject "Hypersensitive reaction (HR)"

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Die Bedeutung von AQUAPORIN INTERACTOR 1 (AQI1) für die Zelltodregulation in Pflanzen
(2014) Glink, Eva Katharina; Pfitzner, Artur J. P.
Programmed cell death (PCD) is an important process during development, senescence and pathogen defence in plants and in animals. It is a genetically regulated and targeted cell suicide of single cells, for benefit of the whole organism. In plants, PCD is of great importance, especially in the course of the “hypersensitive response” (HR). For protecting themselves against harmful intruders, infected plant cells are directly deposed of by PCD. The developing local lesions act as a barrier between host plant and pathogen. This prevents the systemic expansion of biotrophic pathogens within the whole plant. The induction of PCD involves complex signal transduction pathways. Reactive oxygen species (ROS), in particular H₂O₂, play an important role as signal molecules during PCD. The transport of H₂O₂ across cell membranes is conducted by aquaporins. As the vitality of cells depends on intracellular H₂O₂-levels, a spatiotemporal control of this H₂O₂-transport is indispensable. AQUAPORIN INTERACTOR 1 (AQI1) was isolated as a potential regulator of the channel function of aquaporins. AQI1 is a plant protein with sequence homology to the mammal aminoacylase 1. It is known, that aminoacylases catalyse the hydrolysis of acyl-amino acids. However, the physiological function of these enzymes is still unclear. This study represents the first characterisation of an aminoacylase (AQI1) in plants. The physiological function of AQI1 as a regulator of aquaporins, as well as the underlying molecular mechanisms, have been analysed. In addition to deacetylation of amino acids, a second function of the protein AQI1 was discovered. AQI1 interferes with the channel activity of aquaporins by protein-protein interaction. In this way, AQI1 is able to inhibit the H₂O₂-, and to a certain extent also the H₂O-influx, through aquaporins. Probably, this happens by blocking the aquaporinpore. Due to this function, AQI1 is a major component in cell death regulation in plants. During the „hypersensitive response“ (HR), which is induced as a result of pathogen attack, AQI1 accumulates to high levels to prevent the influx of toxic amounts of H₂O₂ into neighbouring cells. This ensures a local control of PCD. In addition, AQI1 seems to be involved in regulation of senescence processes. It could be demonstrated, that AQI1 accumulates in a gradient from juvenile to senescent leaves, due to degradation in older tissues. By this age-dependent accumulation, AQI1 could contribute to the vitality of leaves, by preventing the influx of excessive amounts of H₂O₂ into the cell.