Biomedical Engineering Reference
In-Depth Information
May et al.
26
have recently developed an
Agrobacterium
-based genetic transfor-
mation system for banana using shoot tip plant cultures. Their goal was to use this
technology to the benefit of developing countries by modifying desirable agronomic
and post-harvest characteristics of potential new varieties in order to increase their
suitability for transport and storage in international trade, and therefore, stimulating
the economies of export nations. The onset of fruit ripening entails the coordinated
expression of an array of associated proteins. While much work has been performed
on the analysis of gene expression in the ripening fruits of tomato, avocado, and
apple, little is known about the specific changes in gene expression that occur during
banana fruit ripening. May et al.
26
are investigating the regulation of, and the changes
in, gene expression in ripening banana fruit. Banana differential cDNA and genomic
libraries have been constructed and screened with a variety of heterologous ripening
related cDNAs [i.e., EFE, polygalacturonase (PG)]. Several clones have been isolated
and their sequences have been determined. Using a
Musa
transformation technology
developed in their laboratory, these workers were aiming to determine the patterns
of expression of such regulatory sequences controlling gene expression during
banana fruit ripening. They have reported the relative abundance of a variety of
mRNAs present in banana fruits during seven separate stages of ripening. Huang
et al.
27
have also been working with the cloning and analysis of the mRNAs involved
in the ripening of banana. They have cloned the ACC synthase and the ACC oxidase
specific for fruit ripening. They have also found that the expression of the ACC
oxidase gene occurs earlier than that of the ACC synthase gene during ripening.
Moreover, there was a high level of mRNA accumulation for ACC oxidase in each
ripening stage. The expression of both ACC synthase and ACC oxidase genes could
be induced by 10 µl/l of exogenous ethylene. Hurst et al.
28
proved that the glutamine
synthetase (GS) enzyme is very important in the shelf life of asparagus; if this
enzyme is inhibited its shelf life is reduced. Although this inhibition results in a
huge increase in ammonia (which is toxic) in spear tips, they concluded that
glutamine depletion rather than ammonia toxicity could be the reason for the reduc-
tion of asparagus shelf life. Thus, an approach in order to extend the asparagus shelf
life could be the over-expression of the GS gene (tissue specific) to reassimilate
considerable amounts of ammonia in the tips.
I
NCREASING
S
OLIDS
C
ONTENT
Research being conducted on tomato nowadays is already beginning to make an
impact on the food and processing industries. Because of the tomato crop's financial
importance, several major projects are being conducted.
17
Consumers like a thick
tomato sauce, but the thicker the sauce, the higher the production costs. Tomatoes
are 95% water and the more water that has to be removed from tomatoes the higher
the cost of processing.
4,17
Several projects are being directed in order to develop
tomatoes with a higher ratio of solids to water; just a 1% increase in the solids
content could result in substantial economic savings because less water would have
to be removed during processing.
16,17
Tomatoes with a higher solids content more
than just save time and energy during processing; they also result in higher quality
products. One of the most important quality components in processing tomatoes is
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