The free radical scavenging system in overcoming phytotoxicity and breaking dormancy Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/m900nx09k

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  • Hydrogen cyanamide (CY) induced earlier budbreak, more uniform and a higher percentage of budbreak in resting poplar (Populus alba x P. gradidentata, NC 5339) plants. However, it was phytotoxic to poplar when applied at 0.5 M or higher concentrations. Percent budbreak increased and percent dieback decreased when poplar plants were treated with mixtures of CY and cysteine (Cys) compared to CY treatment alone. The levels of total glutathione and reduced glutathione (GSH) and activity of glutathione reductase (GR) decreased and amounts of oxidized glutathione (GSSG), ethylene and ethane and activity of glucose-6-phosphate dehydrogenase (G6PDH) increased with CY treatment in poplar. Mixing CY with Cys in vitro reduced the percentages of CY and Cys remaining in the mixtures over time. Hydrogen cyanamide was phytotoxic to bromegrass (Bromus inermis L.) cells in suspension cultures while cysteine reduced CY-induced phytotoxicity. In bromegrass cells, 2,3,5-triphenyl tetrazolium chloride (TTC) reduction, cell regrowth and levels of total glutathione, GSH and GSSG, and activities of G6PDH and catalase, and contents of protein, malondialdehyde (MDA) and ethane decreased with CY treatment. Activities of GR, peroxidase were not affected and superoxide dismutase (SOD) increased slightly in 1 mM CY treatment for 24 hour incubation. These enzyme activities decreased in 5 mM CY treatment at the same incubation time. In ABA-treated bromegrass cells, TTC reduction and amounts of total glutathione, GSH, NADPH, protein, ethylene and activities of G6PDH, SOD, GR and catalase were higher or greater and amounts of GSSG and ethane were lower than those of -ABA control after freezing stress. Peroxidase activity and MDA content of -ABA control decreased with freezing treatment. Peroxidase activity of ABA-treated cells decreased at +4°C and did not change at -9°C. MDA content of ABA-treated cells was not affected by freezing treatment. These studies suggest that thiol containing compounds react directly with CY. The increased budbreak and reduced phytotoxicity of dormant poplar plants caused by mixing CY with SH containing compounds may be due to the reduction of CY concentration. Hydrogen cyanamide or freezing stress may injure bromegrass cells or dormant poplar plants by damaging the free radical scavenging system. ABA may protect bromegrass cells from freezing stress by maintaining or activating the free radical scavenging system.
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