Biochemistry of Flower Senescence - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 59

of ethylene action. The elevation of CO 2 level was accompanied by a reduction of O 2 to
2% and storage at low temperature (0 ◦ C). The authors reported that the potential benefit of
this treatment as well as a commercial use is very limited.

4.4.2 Chemical inhibition of ethylene perception

4.4.2.1 2,5-Norbornadiene
In the early seventies, several alkenes have been reported by Sisler and Pian (1973) as
effective ethylene antagonists. The most stabile of these compounds was 2,5-norbornadiene
(2,5-bicyclohepta-2,5-diene; NBD). NBD is a liquid with a low boiling point (89 ◦ C) that
easily vaporizes at room temperature, which makes it easy to treat plant material in airtight
chambers. NBDs effectiveness in preventing ethylene effects was tested on different plant
materials, including carnation flowers (Sisler et al., 1986). Continuous treatment of carnation
flowers with NBD, even at lowest concentration tested (500 L/L), strongly increased

vase life of the flowers and delayed the onset of climacteric ethylene production. Higher
concentrations of NBD inhibited ethylene binding in carnation flowers and leaves with 66
and 86%, respectively. Even though NBD is commercially available, its very disagreeable
odor limits its use to scientific investigations (Sisler and Serek, 1999). Additionally, NBD is
blocking the receptor in a competitive manner and, therefore, has to be continuously present
to counteract ethylene effects. Therefore, NBD has very limited potential for commercial
use (Sisler et al., 1990).

μ

4.4.2.2 Silver thiosulfate
The silver ion has proved to be a potent inhibitor of ethylene action in ornamentals. Ethylene-
binding studies using radio-labeled ethylene have shown that STS treatment blocks the
binding of ethylene (Sisler et al., 1986). ETR1 has been shown to contain a copper ion
that coordinates the binding of ethylene (Rodrigez et al., 1999), and the action of STS
may be related to the exchange between copper and silver ions in the receptor protein.
The silver-containing receptor apparently is locked in such a state that ethylene cannot
bind and induce a conformational change (Knee, 1995). For a number of years, STS was
the only compound used commercially to protect ornamental crops against ethylene at
the receptor level. STS is generally applied as a pretreatment solution to cut flowers. The
persistence and mobility of STS allows very short pulse treatments. In potted plants STS
is applied as an aqueous spray. Beneficial effects of STS are reported for a great variety of
cut flowers and potted plants. STS treatment prevents petal senescence induced by ethylene
and prolongs the vase life in, for example, carnation, D. barbatus , Gypsophila, Matthiola,
Trachelium, Physostegia , and several orchid species. However, byproducts of use can lead
to environmental contamination.

4.4.2.3 Diazocyclopentadiene
Years after the discovery of NBD and STS, new compounds have been tested for extending
the postharvest life of ornamental crops. Diazocyclopentadiene (DACP) has been tested on
different ornamental crops, like carnations, miniature roses, and sweet pea flowers (Serek
et al., 1994). DACP binds weakly to the ethylene receptor (Sisler and Serek, 1997), but
under fluorescent light, DACP decomposes to unknown compounds and becomes a very
effective ethylene receptor blocker. The active product of decomposition of DACP has not