Nitric oxide signals ROS scavenger-mediated enhancement of PAL activity in nitrogen-deficient Matricaria chamomilla roots: side effects of scavengers.
Owing to the abundance of phenolic metabolites in plant tissue, their accumulation represents an important tool for stress protection. However, the regulation of phenolic metabolism is still poorly known. The regulatory role of reactive oxygen species (ROS) in the activity of phenylalanine ammonia-lyase (PAL) in nitrogen (N)-deficient chamomile roots treated for 24 h was studied using three ROS scavengers [dithiothreitol (DTT), salicylhydroxamic acid, and sodium benzoate]. Scavengers decreased the level of hydrogen peroxide and/or superoxide (and up-regulated ascorbate/guaiacol peroxidase and glutathione reductase), but, surprisingly, stimulated PAL activity. This up-regulation was correlated with increases in nitric oxide (NO) content, total soluble phenols, selected phenolic acids, and, partially, lignin (being expressed the most in DTT-exposed roots). We therefore tested the hypothesis that NO may be involved in these changes. Application of 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) decreased PAL activity and the accumulation of soluble phenols in all treatments. Exogenous H(2)O(2) and NO also stimulated PAL activity and the accumulation of phenols. We conclude that NO, in addition to hydrogen peroxide, may regulate PAL activity during N deficiency. The anomalous effect of PTIO on NO content and possible mechanism of ROS scavenger-evoked NO increases in light of the current knowledge are also discussed.
Kovácik
Jozef
J
Department of Botany, Institute of Biology and Ecology, Faculty of Science, Safárik University, Mánesova 23, 041 67 Kosice, Slovak Republic. jozkovacik@yahoo.com
Klejdus
Borivoj
B
Backor
Martin
M
D003497:Cyclic N-Oxides / Q000494:pharmacology; D004229:Dithiothreitol / Q000494:pharmacology; D016166:Free Radical Scavengers / Q000494:pharmacology*; D006861:Hydrogen Peroxide / Q000037:antagonists & inhibitors / Q000378:metabolism; D062385:Hydroxybenzoates / Q000378:metabolism; D007093:Imidazoles / Q000494:pharmacology; D008031:Lignin / Q000378:metabolism; D031168:Matricaria / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D009569:Nitric Oxide / Q000378:metabolism*; D009584:Nitrogen / Q000172:deficiency*; D010636:Phenols / Q000378:metabolism; D010650:Phenylalanine Ammonia-Lyase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018517:Plant Roots / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012457:Salicylamides / Q000494:pharmacology; D015398:Signal Transduction; D020160:Sodium Benzoate / Q000494:pharmacology; D013481:Superoxides / Q000037:antagonists & inhibitors / Q000378:metabolism; D015854:Up-Regulation
D003497:Cyclic N-Oxides; D016166:Free Radical Scavengers; D062385:Hydroxybenzoates; D007093:Imidazoles; D010636:Phenols; D017382:Reactive Oxygen Species; D012457:Salicylamides; D013481:Superoxides; C079391:2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide; D009569:Nitric Oxide; C005703:salicylhydroxamic acid; D008031:Lignin; D006861:Hydrogen Peroxide; D010650:Phenylalanine Ammonia-Lyase; C017616:phenolic acid; D009584:Nitrogen; D020160:Sodium Benzoate; D004229:Dithiothreitol