Climacteric and Non-climacteric Ripening - Fruit Ripening: Physiology, Signalling and Genomics - page 10

into the ripening mechanism based on
many new discoveries. The unknown
factors and new queries that have emerged
recently will help clarify the mechanism.
A relatively low-level peak in ethylene
production in non-climacteric fruits was
detected recently using continuous high-
precision measurements in strawberry
and grape. These discoveries suggest a
relationship between ethylene and fruit
ripening in fruits classically categorized as
non-climacteric. However, the concrete
function and involvement of ethylene in
the ripening process remains unknown.
The transition from system I to system II
at the onset of ripening is based on the
participation of different ACS genes,
although the regulation of ACS differs in the
two systems (i.e. both negative- and
positive-feedback mechanisms have been
observed) (Barry et al. , 2000; Yokotani et al. ,
2009). ABA may play a role in the transition
stage because its accumulation is induced
prior to the system II ethylene burst.
Alternatively, changes in the accumulation

or balance of ABA and/or other hormones
may serve as a trigger for system II.
Moreover, it is not clear whether the signal
for the initiation of system II originates from
the seed or is derived from another factor.
The discovery of RIN revealed the
master regulator of the fruit-ripening
process. The ripening cascade is con-
sidered to be a common pathway in the
fruit-ripening process regardless of the fruit
category. Additionally, various tran-
scription factors have been identifi ed by an
exhaustive analysis, and their involvement
in the ripening process has been discussed
(Manning et al. , 2006; Lin et al. , 2008;
Vrebalov et al. , 2009; Martel et al. , 2011).
However, the key signal for the activation
of these transcription factors has not been
determined.
Many questions remain to be addressed
within the fi eld of fruit ripening, as
described above. In the future, additional
experimental approaches derived from
various research areas will be required to
answer these complex questions.

References

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