Food
1(1)
, 1-22
©2007 Global Science Books
tation into the skin cells. The transcript levels of both trans-
porters are lower at post-
véraison
than at pre-
véraison
, but
significant levels of expression were detected. It is sug-
gested that VvKUP1 and VvKUP2 may therefore continue
to contribute to potassium homeostasis throughout berry
development. Other mechanisms may also be involved after
véraison
(Davies
et al
. 2006).
The levels of potassium in grape berries may be
affected by numerous factors including potassium level in
the soil, grape variety, and viticultural practices (Mpelasoka
et al
.
2003; Davies
et al
. 2006). A detailed knowledge of
the mechanisms involved in potassium transport from the
soil, xylem and phloem translocation through the vine and
its accumulation in the berry, is crucial in order to develop
strategies which may reduce its excessive accumulation in
grape berries and thereby improve fruit and wine quality.
Other minerals, such as calcium and magnesium,
together with minimal amounts of sodium and iron, are also
present in grape berries. Calcium concentration is at its ma-
ximum at
véraison
, and remains stable or decreases during
maturation. Calcium has a significant role in the resistance
against
Botrytis cinerea
infection. In must, its content (80
mg/L) can slightly decrease because of the increase of cal-
cium tartrate resulting from alcohol formation. Magnesium,
a component of chlorophyll, is present in grapes and in
must at levels similar to calcium. Grapes are poor in iron
and copper, their concentrations in must and wine being ap-
proximately 10 and 1 mg/L, respectively. However, an unu-
sual increase of these compounds in must can occur as a re-
sult of viticulture and vinification practices. Copper affects
wine flavour by oxidizing thiol-containing compounds
(Blouin and Cruège 2003).
SUGAR IN GRAPE BERRY AND WINE
Sugar transport and accumulation in berry
Efficient assimilation and use of nutrients by plants is of
prime importance for the optimization of crop productivity.
Grape berries, as typical “sink organs”, rely on the use of
available carbohydrate resources produced by photosynthe-
sis to support their growth and development. The transport
and allocation of sugars between the photosynthetic “source
tissues” and the heterotrophic “sink tissues” is known as as-
similate partitioning and is a major determinant of plant
growth and productivity