Ethylene Perception and Gene Expression - Postharvest Biology and Technology of Fruits, Vegetables, and Flowers - page 131

were isolated and expression patterns determined in strawberry ( Fragaria ananassa ) fruits
(Trainotti et al., 2005). The FaEtr1 mRNA was low in flowers, but showed an increase in
the small green fruits and a subsequent decrease in the large green fruits that was followed
by a steep increment, which continued throughout the ripening phase. The FaErs1 mRNA
was very high in flowers but steadily decreased to reach a minimum in the large green
fruits. Afterward, it increased again till the ripening was completed. On the other hand,
FaEtr2 mRNA increased about threefold to reach a maximum in the white fruits. Afterward,
although a slight decrease was observed, the transcript amount remained high in the red fruits
at well over twice that of the small green fruits. The FaEtr1 and FaEtr2 genes were more
responsive to ethylene in the white fruits, while FaErs1 was highly responsive to ethylene
at the red stage. This study suggested that ethylene receptors might have a physiological
role in the ripening of nonclimacteric strawberries.
Even though citrus ( Citrus sinensis ) fruits are nonclimacteric, exogenous ethylene is
able to stimulate ripening by accelerating respiration and inducing pigment changes of
peel, chlorophyll degradation, as well as carotenoid biosynthesis. In young “Valencia”
fruitlets, CsERS1 expression was detected in fruits on tree, immediately after harvest, and
was further induced in the subsequent days (Katz et al., 2004). The CsERS1 expression
was slightly induced by ethylene treatment and reduced by 1-MCP treatment in young
fruitlets. The CsETR1 expression was constitutive in young fruitlets, but was not affected
by detachment from the tree and was ethylene-independent. In mature fruit, the expression
of both CsERS1 and CsETR1 genes was constant and was not affected either by 1-MCP or
propylene treatments. The differences in the expression of CsERS1 between young fruitlets
and mature fruit suggest that CsERS1 may modulate the differential sensitivity to ethylene
in fruitlets versus mature citrus fruit.
6.4 Ethylene perception in flowers
The postharvest quality of many flowers is limited by the increased synthesis and action of
the plant hormone ethylene. Increased production of ethylene plays a role in the senescence
or death of flower petals, abscission of plant parts including floral structures, and discol-
oration of harvested foliage. Abscised and senesced flowers show reduced visual impact,
increase the incidence of infection from Botrytis and other saprophytic pathogens, thus
diminishing the commercial value of flowers.
Just like fruits, flowers are categorized as being climacteric or nonclimacteric. In cli-
macteric flowers such as carnations, Gypsophila , and orchids, senescence is accompanied
by a sudden, transient increase in ethylene production and respiration, while treatment of
nonsenescent flowers with ethylene rapidly induces petal senescence. In nonclimacteric
flowers such as gladiolus, tulip, and iris, generally, no increases in ethylene production
and respiration are apparent during flower senescence, and exogenous ethylene applica-
tion has little or no effect on petal senescence (Serek et al., 2006). Several studies to date
suggest that abscission and senescence of flowers may be triggered by the perception of
endogenous ethylene by ethylene receptors. Abscission is a typical ethylene response in-
duced through ethylene receptors and is influenced by mutations in ethylene receptors
(Patterson and Bleecker, 2004). Therefore, investigations of ethylene receptors and associ-
ated signal transduction pathways are essential for understanding of ethylene perception in
flowers.