Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

BIOCHEMISTRY OF FLOWER SENESCENCE 61
1-Decylcyclopropene (1-DCP) showed the best performance: both in terms of a very low
necessary concentration for maximum protection, 0.3 nL/L; and the longest duration of
action, 36 days. Although these studies were made in banana fruits, there is little doubt
that these compounds will be very effective in protecting flowers from ethylene effects as
well. One could speculate that the longer lasting effect could be due to the hydrophobic
side chain anchoring the compound to the cell membrane, thereby preventing the molecule
from getting lost from the cell surface and, at the same time, allowing a larger amount
of compound to be bound to the tissue. This slow-release effect could then result in the
compound being bound to ethylene receptor molecules, synthesized long after the initial
treatment, thereby prolonging the effect. In flowers the most thoroughly investigated of these
compounds is 1-octylcyclopropene (1-OCP). It has been tested in Kalanchoe blossfeldiana
(Sisler and Serek, 2003) and L. odoratus (Kebenei et al., 2003). Generally, this compound
was equally or slightly more efficient than 1-MCP (compared on a concentration v/v basis)
as a protective agent against ethylene action in flowers. Also, 1-hexylcyclopropene (1-HCP)
has been shown to be effective in Kalanchoe, though in somewhat higher concentrations
(Kebenei et al., 2003).
4.5 Regulation of senescence-related gene
expression by ethylene
The plant hormone ethylene has been implicated in the regulation of both fruit ripening and
leaf and flower senescence (Abeles et al., 1992). A number of senescence regulated (SR) and
ripening-related genes have been found to be upregulated by the exogenous application of
ethylene (Davies and Grierson, 1989; Lawton et al., 1990; Grbic and Bleecker, 1995; Weaver
et al., 1998). Treatment of preclimacteric flowers with ethylene results in the induction of all
the SR genes identified from carnation (Jones and Woodson, 1999). In tomato, the highest
level of expression of pTOM genes in fruit was detected at the orange stage when ethylene
production was highest and enhanced expression in leaves coincided with the first visible
symptoms of leaf yellowing. Treatment with exogenous ethylene resulted in increased
expression of pTOM genes in fruit and leaves, providing evidence that ethylene-controlled
gene expression is involved in both fruit ripening and leaf senescence (Davies and Grierson,
1989).
Never ripe (NR) tomatoes, which are insensitive to ethylene due to a mutation in the
ethylene receptor, produce fruit in which ripening is inhibited, have flower petals that do not
senesce, and have leaves with delayed leaf yellowing (Lanahan et al., 1994). In the fruit of
NR tomatoes, ripening-related transcripts accumulate too much lower levels than in wildtype
fruit (DellaPenna et al., 1989). Arabidopsis plants with a mutated ethylene receptor,
etrl-1, also show delayed leaf senescence but, once initiated, the process of senescence
and the level of SAG expression is similar to that detected in wild-type leaves (Grbic and
Bleecker, 1995). The treatment of tomato plants with the ethylene action inhibitor, silver
thiosulfate, delays both fruit and leaf senescence and greatly reduces the expression of the
mRNAs for pTOM31, pTOM36, and pTOM137 and to a lesser degree pTOM13, pTOM66,
and pTOM75 in both fruit and leaves (Davies and Grierson, 1989). Treatment of carnation
flowers with the ethylene action inhibitor, norbornadiene (NBD), delays the age-related
accumulation of all SR genes except SR5 (Lawton et al., 1990; Woodson et al., 1992,
1993). Treatment with NBD also reduces the basal levels of DCCP1 transcript in petals