Turgor and net ion flux responses to activation of the osmotic MAP kinase cascade by fludioxonil in the filamentous fungus Neurospora crassa |
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Authors: | Roger R Lew |
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Institution: | 1. Institute of Biogeochemistry and Pollutant Dynamics, Federal Institute of Technology (ETH), ETH-Zentrum CHN, Universitätstrasse 16, CH-8092 Zurich, Switzerland;2. Institute of Geochemistry and Petrology, Federal Institute of Technology (ETH), ETH-Zentrum NO, Clausiusstrasse 25, CH-8092 Zurich, Switzerland;3. Institute of Evolutionary Biology and Environmental Studies, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland;1. Institute of Botany, Faculty of Biology, Jagiellonian University, Gronostajowa 3, 30-387 Kraków, Poland;2. Department of Plant Physiology and Development, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland;3. Department of Plant Physiology and Biochemistry, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, 30-387 Kraków, Poland;1. Department of Pharmacognosy and Botany, University of Veterinary Medicine and Pharmacy, Komenského 73, 041 81 Ko?ice, Slovak Republic;2. Department of Botany, Institute of Biology and Ecology, Faculty of Science, ?afárik University, Mánesova 23, 041 67 Ko?ice, Slovak Republic;3. Institute of Hygiene, Faculty of Medicine, ?afárik University, ?robárova 2, 041 80 Ko?ice, Slovak Republic |
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Abstract: | The internal hydrostatic pressure (turgor) of the filamentous fungus Neurospora crassa is regulated at about 400–500 kiloPascals, primarily by an osmotic MAP kinase cascade which activates ion uptake from the extracellular medium and glycerol synthesis. In the absence of hyperosmotic stress, the phenylpyrrole fungicide fludioxonil activates the osmotic MAP kinase cascade, resulting in cell death. Turgor, the electrical potential and net ion fluxes were measured after treatment with fludioxonil. In wildtype, fludioxonil causes a hyperpolarization of the plasma membrane and net H+ efflux from the cell, consistent with activation of the H+-ATPase. At the same time, net K+ uptake occurs, and turgor increases (about 2-fold above normal levels). None of these changes are observed in the os–2 mutant (which lacks a functional MAP kinase, the last of the three kinases in the osmotic MAP kinase cascade). Tip growth ceases as hyperpolarization, net ion flux changes, and turgor increases begin. The inappropriate turgor increase is the probable cause of eventual lysis and death. The results corroborate a multi-pathway response to hyperosmotic stress that includes activation of plasma membrane transport. The relation to cell expansion (tip growth) is not direct. Increases in turgor due to ion transport might be expected to increase growth rate, but this does not occur. Instead, there must be a complex regulatory interplay between the growth and the turgor driving force, possibly mediated by regulation of cell wall extensibility. |
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