Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

56 POSTHARVEST BIOLOGY & TECHNOLOGY OF FRUITS, VEGETABLES, & FLOWERS
Gladiolus is an ethylene-insensitive flower. Exogenous ethylene and ethylene inhibitors
have no effect on the petal senescence process. To study which processes in gladiolus
are associated with changes in ethylene perception, two types of gladiolus genes, named
GgERS1a and GgERS1b, respectively, homologous to the Arabidopsis ethylene receptor
gene ERS1 were isolated by Arora et al. (2006). GgERS1a is conserved in terms of exon
numbers and intron positions, whereas GgERS1b is almost same with GgERS1a except
lacking a 636-nucleotide frame encoding the first and second histidine kinase (HisKA)
motifs. The sequence data on full length genomic DNA indicated that both GgERS1a and
GgERS1b were spliced from different genomic DNA. As the result of mRNA expression
study, in spite of lacking the two significant motifs, the expression of GgERS1b dramatically
changed with advance in petal senescence, whereas the level of GgERS1a was expressed
highly and constitutively. The result suggests that both the genes possess a significant role
for the subfunctionalization process to provide ethylene insensitivity in gladiolus flowers
(Arora et al., 2006).
Nitric oxide (NO) gas is also effective in extending the postharvest life of flowers through
modulating endogenous ethylene activity (Badiyan et al., 2004). The gaseous nature of NO,
however, requires postharvest infrastructures that may not always be readily available, and
therefore the treatment will be less suitable than liquid-pulsing solutions. To this end, an NO
donor compound (DETA/NO) applied in the vase water has been used to extend the vase
life of flowers. The effectiveness of DETA/NO across ethylene-sensitive and -insensitive
flowers suggests that it may have significant commercial application in the future (Badiyan
et al., 2004). The mode of action of NO in delaying the onset of flower senescence has yet
to be studied at the molecular level.
An experiment was conducted to study the effect of 5-sulfosalicylic acid (5-SSA) on
the vase life of cut flowers of gladiolus (Ezhilmathi et al., 2007). The vase solution having
5-SSA significantly increased cumulative uptake of vase solution, vase life, number of
opened florets, and decreased the number of unopened florets compared to the controls.
Spikes kept in vase solution containing 5-SSA also exhibited lower respiration rates, lipid
peroxidation, and lipoxygenase activity, and higher membrane stability, soluble protein
concentration, and activity of superoxide dismutase and catalase. Results suggest that 5-SSA
increases vase life by increasing the reactive oxygen species-scavenging activity of the
gladiolus cut flowers.
4.4 Ethylene action and methods for inhibiting ethylene responses
A range of methods are available for preventing the deteriorative effect of ethylene on
postharvest characteristics of ornamental crops. Interfering with the plant’s response to
ethylene can in principle be achieved by (1) inhibition of the plant’s own ethylene production;
(2) blocking the binding of ethylene to its receptor; and (3) by blocking the plant’s reaction
to the binding of ethylene to the receptor.
Interference with the biosynthesis of ethylene in ornamental plants can be achieved by
blocking components of the ethylene synthesis pathway. During many years, several chemicals
have successfully been used by the floral industry. AVG (1-aminoethoxyvinylglicine)
and AOA (aminooxyacetic acid), both inhibitors of the conversion of S-adenosyl-methionine
(SAM) to 1-aminocyclopropane-1-carboxylic acid (ACC) have been shown effective in
blocking the increase in ethylene production that accompanies senescence in a variety of