Abstract:
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.
