Bananas - Crop Post-Harvest: Science and Technology - page 35

of the pulp and peel to produce endogenous C 2 H 4 in cv
'Dwarf Cavendish' (AAA, Cavendish subgroup) as the
fruit ripened. They separated the pulp and peel while the
fruit was green and then monitored C 2 H 4 production by
each tissue. Seven days after the experiment began the pulp
began to produce C 2 H 4 , and maximum C 2 H 4 production
occurred 2 days later. After this, C 2 H 4 production by the
pulp decreased. The peel produced very little C 2 H 4 during
ripening, but some appeared when senescence began after
12-13 days. ACC oxidase activity differed between the
peel and pulp. In the pulp, ACC oxidase activity rose and
fell following the pattern of C 2 H 4 evolution, indicating a
close link between the two. In contrast, in the peel ACC
oxidase activity began to increase 8 days after the experi-
ment began and continued to increase until senescence. In
the peel, there was no link between ACC oxidase activity
and C 2 H 4 evolution. However, Dominguez and Vendrell
(1993) showed that the peel is well able to generate C 2 H 4
provided sufficient 1-aminocyclopropane-1-carboxylic
acid (ACC) substrate is supplied. They proposed that the
ACC oxidase activity of the pulp was important for starting
the autocatalytic C 2 H 4 production needed for ripening. The
response of the peel was then governed by the diffusion of
C 2 H 4 from the pulp. The banana ripens from the inside out,
supporting observations of Wardlaw and Leonard (1940)
on cv Gros Michel (AAA group, Gros Michel subgroup).
Dominguez and Vendrell (1994) subsequently obtained
similar results to their earlier work by exposing either the
whole fruit or slices or separate pieces of peel and pulp to
exogenous C 2 H 4 . The pulp responded by increasing C 2 H 4
production but the peel showed only a temporary increase
and then returned to control levels. They suggested that
the peel did not have the capacity for autocatalytic C 2 H 4
production that was a feature of the pulp.
Moya-León and John (1994) point out that ACC oxidase
requires ascorbate as a co-substrate and iron and carbon
dioxide as co-factors for full expression of activity. They
were concerned that the results of Dominguez and Vendrell
(1993) could have been influenced by lack of co-substrate
and co-factors for ACC oxidase. They added these to the
peel and the pulp in their studies on ACC oxidase activity
in cv Cavendish (AAA) bananas from the Caribbean.
Moya-León and John (1994) obtained results that differed
from those of Dominguez and Vendrell (1993) in one
important respect. The peak in ACC oxidase activity in the
pulp during ripening, observed by Dominguez and Vendrell
(1993), did not occur when the co-substrate and co-factors
were added. They suggested that this did not support the
view that C 2 H 4 production by the pulp triggered ripening in
banana because the pulp is unable to sustain C 2 H 4 evolution

if ACC oxidase is limited by the supply of co-substrate or
co-factors. Moya-León and John (1994) do not present any
data on the C 2 H 4 evolution of the whole fruit, pulp or peel
in the absence of added ACC, and so it is not clear what is
happening during the course of ripening in the fruit that
they used. Dominguez and Vendrell (1993) separated the
peel and pulp while the fruit were green and the two tissues
ripened independently of one another. In addition, they
showed that wound C 2 H 4 lasted for only 24 hours and was
far removed in time from the initiation of ripening.
In contrast, Moya-León and John (1994) seem to have
separated the peel and pulp during the course of ripening.
In their case, the pulp and peel have ripened together in the
intact fruit and the one may influence the behaviour of the
other, as well as confounding any effect of the wounding
on C 2 H 4 production.
Inaba et al . (2007) point out that the evolution of C 2 H 4
during the ripening of banana fruit is unique in that it rises
to a peak within a day or two of the start of catalytic C 2 H 4
production and then declines. This contrasts with other
climacteric fruit where C 2 H 4 evolution continues at a high
rate. The peak in C 2 H 4 production in banana can be readily
observed in the data of Banks (1985b), Dominguez and
Vendrell (1993, 1994), Golding et al . (1998) and van Luan
et al . (2003), among others. Chilling injury (van Luan et al .
2003) or coating the fruit (Banks 1985b) modifies the
pattern of C 2 H 4 evolution by flattening and extending the
peak.
Even though the fruit consists of two morphologically
different tissues, the pattern of evolution of C 2 H 4 from the
whole fruit during ripening is dominated by the behaviour
of the pulp. Golding et al . (1998) used 1-methylcyclopropene
(1-MCP), a nonreversible blocker of C 2 H 4 receptor sites, to
investigate the role of C 2 H 4 in the different stages of
ripening. If 1-MCP stops or delays a process, this infers
that the process is influenced by C 2 H 4 . 1-MCP was applied
either when the fruit were green or at 6, 12 or 24 hours after
the fruit were exposed to propylene to initiate ripening.
1-MCP delayed all ripening processes when applied either
to green fruit or to fruit at 6 or 12 hours after ripening was
initiated. However, at 24 hours after ripening began,
1-MCP did not alter the climacteric peaks of C 2 H 4 evolution
or respiration but did affect de-greening and the
production of volatiles. All fruit treated with 1-MCP
showed an increased production of C 2 H 4 , when it did occur,
and a reduced rate of respiration. Propylene supplied
continuously to fruit, suppressed C 2 H 4 production and
Golding et al . (1998) interpret this as a suppression of
either ACC synthase and ACC oxidase or an increased
conversion of ACC to the inactive malonyl-ACC. Each of