A replacement for silver thiosulphate as a commercial post-harvest treatment
needs to be found. The longevity of cut carnation flowers is extended by all
concentrations of ethanol tested. Compared to a water control, the vase-life of
ethanol-treated flowers is between 150 and 250% longer. The greatest longevity
increases are recorded with 3% ethanol. The use of ethanol as a post-harvest
treatment was tested. The longevity increase as a result of ethanol application only
occurs if the ethanol is applied as a holding solution. Pulse treatments are not
effective at delaying the senescence of the flowers. The sooner the ethanol is
applied, the greater the increase in vase life. If ethanol treatment is halted at any
point during the experiment, the longevity of the flowers is reduced. It was observed
that the longer the stems of ethanol-treated flowers, the greater the longevity
increases. The ethanol holding solution does not prevent the action of external
ethylene, thereby restricting the potential of ethanol as a commercial post-harvest treatment.
Physiologically, flowers treated with ethanol exhibit a different senescence
process to control flowers. The typical in-rolling of the petals of carnation flowers is
not seen, instead the petals appear burnt. The ovaries are also notably effected by
ethanol, being smaller and more yellow in colour. Ethanol treatment results in
longevity increases by inhibiting the formation of ethylene, the plant hormone
responsible for senescence. The concentration of the direct precursor to ethylene,
ACC, as well as the activity of the enzyme that converts ACC to ethylene, ACC oxidase, is reduced to almost zero in the tissues of treated flowers. Another physiological factor affected by ethanol treatment is the carbohydrate status of the
flowers. The normal sink activity of the ovary is inhibited by ethanol treatment.
Although the carbohydrate content of the petals is found to decrease sharply in
ethanol-treated flowers, these carbohydrates are not relocated to the ovary. The
ovary does not increase in dry matter or chlorophyll content. The carbohydrate
content decreases as a result of ethanol treatment, and when ¹⁴C sucrose was
applied to petals, no radioactivity was recovered in the ovary. The petals and ovary
are the organs most effect by ethanol activity, as when ¹⁴C ethanol was applied to
cut carnation flowers as a pulse, the majority of the radioactivity was discovered
here. The protein content of cells of both organs decreases significantly compared
to control flowers. This is a total protein loss, rather than the destruction of specific systems.
If the activity of alcohol dehydrogenase is prevented in ethanol-treated
flowers, inhibiting the conversion of ethanol to acetaldehyde, no longevity increases
are seen. The airspace surrounding treated flowers was found to contain ethanol
and small amounts of acetaldehyde. The tissues of flowers treated with ethanol
show an increase in the acetaldehyde content, as well as the ethanol content,
especially in the ovary. The application of acetaldehyde directly to cut carnation
flowers as a holding solution resulted in the vase life of the flowers increased by 150%.
To determine the effectiveness of acetaldehyde as a post-harvest treatment,
various concentrations of acetaldehyde were applied to cut carnation ftowers as a
pulse treatment and a holding solution. Pulse treatments did not increase the vase life of flowers, and resulted in a number of negative effects in the flower. A holding
solution of acetaldehyde does increase the longevity of cut carnation flowers,
provided it is above a certain concentration. Treatments at concentrations below 1%
acetaldehyde appear to promote flower senescence. The use of acetaldehyde as a
post-harvest treatment has many of the same disadvantages as ethanol treatment.
Acetaldehyde must also be applied as a holding solution for as long as possible. If
removed from this solution, death of the organ occurred quickly. Acetaldehyde is
also ineffective against external ethylene. A negative effect of acetaldehyde not
found in ethanol-treated flowers, is that the longer the stem of cut carnation flowers, the shorter the resultant vase life.
Physiologically the responses in cut carnation flowers were very similar to
those seen in ethanol-treated flowers. Acetaldehyde inhibited the formation of
ethylene completely. Almost no ACC can be found in treated tissues, and the action
of ACC oxidase is completely reduced. The petals of acetaldehyde-treated flowers
suffer from severe petal browning, rather than in rolling. The ovaries are particularly
badly effected by treatment. There are large scale losses in fresh weight and
chlorophyll content. The latter results in the ovaries appearing yellow in colour.
They also show a loss in structure. The sink activity of these ovaries is destroyed.
Like ethanol-treated flowers, the carbohydrate content of both the petals and ovaries
are dramatically reduced. When ¹⁴C sucrose was applied to one of the. petals,
almost no radioactivity was recorded in the ovary. There. is also a major loss in
general protein content, slightly more severe than in ethanol-treated flowers. The conversion of ethanol to acetaldehyde is necessary in order to achieve
longevity increases in ethanol-treated flowers. If the conversion of this acetaldehyde
to ethanol is prevented in acetaldehyde-treated flower there is once again no
longevity increase. Both ethanol and acetaldehyde are required within the system to
result in increased longevity. Although ethanol and acetaldehyde treatments result in
decreases in the total protein content of the flowers, certain enzymes remain active.
Alcohol dehydrogenase is a bi-directional enzyme, capable of converting ethanol to
acetaldehyde and then back to ethanol again. The activity of this enzyme, in both
orientations, is increased in ethanol and acetaldehyde-treated flowers. The activity
of pyruvate decarboxylase, which converts pyruvate to acetaldehyde, is also
increased as a result of both treatments. The similarities of the physiological
response of cut carnation flowers to ethanol and acetaldehyde post-harvest
treatments, and the increased activity of these enzymes, indicate that the effect of both compounds on longevity is closely linked. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2000.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/10268 |
| Date | 19 December 2013 |
| Creators | Podd, Lindsey Alice. |
| Contributors | Van Staden, Johannes. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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