Agriculture Reference
In-Depth Information
sucrose concentration may vary, being absent in cherries and berries. The fruit is an
important metabolic sink capable of attracting carbohydrates from different sources
as storage tissues and leaves. In stone fruit and grapes, the increase in reducing
sugars occurs only when the fruit is still attached to the tree. In others (apple, pear,
kiwi, banana), starch represents the main form of sugar accumulation. The maxi-
mum amount of starch varies from fruit to fruit in different species: in the case of
apples and pears it may reach a concentrations ranging from 2-4 % of fresh weight.
This occurs at the final stages of fruit development and, in apple, is associated to
a starch synthase, whose expression levels peaks about 90 DAFB. The increase in
hexoses in pome-fruit occurs during the post-harvest ripening and is the results of
α and β amylase activity on starch. The concentration of starch decreases to values
of 1-2 %, while that of hexoses increases from 1 up to 14-15 %. This process, in
addition with softening, makes the fruit edible.
Fruit flavor develops during ripening and is responsible of the “bouquet”,
which is characteristic of each fruit type and variety. Volatile compounds are pres-
ent as a ppm fraction, and belong to different classes of biochemical compounds,
some of which still unidentified. In peaches and apples, aldehydes and alcohols,
responsible of the herbaceous aroma, are the prevailing volatiles at preclimacteric
stages, while esters and lactones are the most important at climacteric stage. Many
volatile compounds are synthesized in a ripe fruit but only few are responsible
for the characteristic aroma: in apple, for example, only a dozen of the several
hundred volatile compounds identified are important for the aroma definition.
The biosynthetic pathways and regulatory mechanisms that lead to the forma-
tion of individual volatile compounds, defining the “bouquet”, are only partially
known. In the case of grapes, the biosynthetic pathways leading to the formation
of monoterpenes and sesquiterpenes, responsible of the floral note of the grape
berry, have been elucidated. These biosynthetic pathways are generally present
in all fruit species, although their activation and modulation occur differently in
diverse species during fruit ripening.
References
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Bonghi C, Trainotti L, Botton A et al (2011) A microarray approach to identify genes involved in
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Botton A, Eccher G, Forcato C et al (2011) Signaling pathways mediating the induction of apple
fruitlet abscission. Plant Physiol 155:185-208
Castellarin SD, Gambetta GA, Wada H et al (2011) Fruit ripening in
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and ripening of citrus fruit flesh. A proposed mechanism for citric acid utilization. Plant Mol
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