Cut Flowers - Crop Post-Harvest: Science and Technology - page 447

They include up-regulated genes for synthetic enzymes
(e.g. ethylene and amino acid synthesis), hydrolytic and
degradative enzymes (e.g. proteinase, nucleases, lipase,
glucosidase), enzymes that alter fatty acid metabolism and
cell walls and genes associated with signalling and trans-
port (Woodson 1991; Jones et al . 1995a; Jones & Woodson
1999; Rubenstein 2000; Eason et al . 2002; Hunter et al .
2002). Rubenstein (2000) and Hunter et al . (2002) point out
that while these genes are part of the ageing process, they
are not necessarily the genes that initiate the senescence
cascade. The ways in which the senescence-associated
genes are regulated are not clear, though some are ethylene
induced and/or mediated. The trigger that initiates sene-
scence in cut flowers, before increased ethylene synthesis
and before many of the processes described above, is still
not established. The role of signals in senescence is
discussed by Rubenstein (2000).
In addition to the genetic analysis, many other enzyme
changes have been observed, including those associated
with increased pigment synthesis, decreased phospholipid
synthesis and lipid oxidation and breakdown (Borochov &
Woodson 1989; Thompson et al . 1997; Rubenstein 2000).
Treatment with cycloheximide, an inhibitor of protein
synthesis, generally delays flower ageing.
Flowers show some of the characteristics of programmed
cell death, including increased proteinases, nucleases and
DNA fragmentation (Rubenstein 2000; Eason et al . 2002;
Hunter et al . 2002). Senescence of ethylene insensitive
sandersonia, daylily and daffodil flowers and ethylene
sensitive carnation flowers is characterised by increased
proteinase activity, a key regulator of cell death in animals
(Jones et al . 1995a; Rubenstein 2000; Eason et al . 2002;
Hunter et al . 2002; Figure 19.3).
It is not clear whether some of the processes in ageing
petals may be more like a breakdown of cell function and
structure than programmed cell death, e.g. the lipid
oxidation that ultimately leads to membrane leakiness
(Borochov & Woodson 1989; Thompson et al . 1997). In
other words, full understanding of the interacting set of
ageing processes has yet to be realised.
Cut flower development and senescence are at least
partly controlled by plant growth regulators, including
ethylene (Halevy & Mayak 1979, 1981; Mayak & Halevy
1980; Reid & Goszczynska 1985; Mayak 1987; Borochov &
Woodson 1989; Woodson 1991; Wills et al . 1998; Reid
2002; Eason 2006).
Cut flowers can be loosely categorised as either
climacteric, such as carnations, or nonclimacteric, such as
roses, according to whether or not, respectively, ethylene
plays a pivotal role in coordinating their senescence (Wills

Figure 19.1 Flower arranging demonstration in
Tokyo, Japan.

(Halevy & Mayak 1979). For example, provision of
supplementary irradiation increased the vase life of cut
roses (Fjeld et al . 1994).
The processes of flower development and senescence
are highly variable in terms of morphology and physio-
logy among genotypes. Flower initiation, which can be
temperature and/or photoperiod sensitive, is typically
followed by bud development, flower opening, pollination
and senescence. Bud and flower abscission are associated
with reduced longevity in some species (Reid &
Goszczynska 1985; Joyce & Poole 1993; Macnish et al .
1999; Reid 2002). Senescence is often characterised by
colour change (fading) and water loss (wilting) in flowers
and/or leaves (Figure 19.2). Cut flower senescence
usually has some of the characteristics of ageing on the
plant (e.g. biochemical changes, flower opening and petal
death) and some additional characteristics, particularly
water loss.

Physiological changes after harvest
Profound changes in metabolism occur throughout flower
development, ageing and senescence (Mayak & Halevy
1980). Multiple pathways of ageing and senescence go on
in the flower at the one time. Most of these processes
appear to be under tight genetic control. Thus, marked
changes in gene expression, nucleic acid levels and types,
and protein, including enzyme, synthesis take place
(Woodson 1991). The later processes of senescence are
similar in flowers where senescence is controlled by
ethylene and in ethylene insensitive flowers.
There is an increasing record of genes and enzymes that
are up- or down-regulated during ageing and senescence.