Ethephon, ethylene and abscission physiology of camellia : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Horticultural Science at Massey University, Palmerston North, New Zealand
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Date
1992
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Massey University
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Abstract
Ethylene application to leaves and floral buds of Camellia resulted in abscission
with a lag period, the duration of which was dependent on ethylene concentration
and cultivar. During this period, cellulase activity doubled in leaf abscission
zones, and when abscission commenced, activity increased more rapidly.
However, no increase in cellulase activity was observed in floral bud abscission
zones. Propylene application revealed that autocatalytic ethylene production
increased in leaf abscission zones prior to and decreased after abscission.
However, in the leaf blade, no change in endogenous ethylene production was
measured, nor were any signs of leaf senescence observed. Application of(STS)
completely inhibited leaf abscission and delayed and reduced floral bud
abscission in response to applied ethylene. This pointed to a similar role for
ethylene in both organs, but that the abscission process of floral buds occurred at
a faster rate than that of leaves. Application of ethylene for differing durations to
floral buds and leaves demonstrated that regardless of ethylene treatment
duration, abscission ceased less than 24 hr after ethylene removal indicating that
continuous ethylene exposure is required to promote abscission of Camellia
organs.
Measurement of abscission rate (time to 50% abscission) in response to a range
of ethylene concentrations determined that floral buds were more sensitive (that
is; responded more rapidly to lower ethylene concentrations) than leaves.
Ethylene-sensitivity was i nfluenced by organ maturity. As floral buds mature d
from initiation t o flower opening, the rate of ethylene-promoted abscission
i ncreased, i ndicati ng g reater sensitivity. Leaves were most sensitive to ethylene
directly after bud break and sensitivity decreased untiiU weeks after cessation of
stem extension ; after this time, sensitivity did not change significantly over the
next 3 years.
Low temperatures reduced the ethylene-promoted abscission rate of both leaves
and floral buds with an exponential relationship. Low temperatures increased the
ethylene concentration required to saturate the abscission response.
Endogenous ethylene production of Camellia leaves increased with higher
temperatures and peaked at 20 to 25c.
Measurement of abscission rate (time to 50% abscission) in response to a range
of ethylene concentrations determined that floral buds were more sensitive (that
is; responded more rapidly to lower ethylene concentrations) than leaves.
Ethylene-sensitivity was influenced by organ maturity. As floral buds matured
from initiation to flower opening, the rate of ethylene-promoted abscission
increased, indicating greater sensitivity. Leaves were most sensitive to ethylene
directly after bud break and sensitivity decreased until 12 weeks after cessation of
stem extension; after this time, sensitivity did not change significantly over the
next 3 years.
Low temperatures reduced the ethylene-promoted abscission rate of both leaves
and floral buds with an exponential relationship. Low temperatures increased the
ethylene concentration required to saturate the abscission response.
Endogenous ethylene production of Camellia leaves increased with higher
temperatures and peaked at 20 to 25c.
Since ethylene release from ethephon may be described in terms of
concentration and duration of ethylene exposure, the effect of time, temperature ,
cultivar, organ type and organ maturity on organ abscission response to
ethephon application could be explained in terms of the ethylene-promoted
response.
The level of ethylene- and ethephon-promoted abscission were explained in
terms of the interaction of ethylene concentration and duration of exposure with
organ type, organ maturity and temperature which determined the level of
abscission response. Three mechanisms were important in determining the
response to ethylene; ethylene-sensitivity, and rate of reaction and reversibility of
the abscission process. The rate of the abscission process was determined by
ethylene concentration, temperature, organ type and maturity. Since abscission
was reversible in Camellia, the duration of exposure interacted with the
abscission rate to determine the extent of abscission in response to ethylene or
ethephon application.
In conclusion , the greatly expanded understanding of the ethylene-promoted
abscission process carried out in this study facilitates control (promotion or
inhibition) of abscission in Camellia. This enhances the possibility for culture and
transportation of high quality Camellia plants from New Zealand.
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Keywords
Camellia, Ethylene, Abscission