Agriculture Reference
In-Depth Information
dominant amino acids. The distribution of these compounds through the berry is not
homogenous and varies with developmental stage. The purpose of these changes in
composition is to aid seed dispersal by appealing to a bird's sense of sight, smell
and taste.
Berry composition is sensitive to the environment and can be manipulated to
some extent with management practises. For instance, leaf removal from the fruit-
ing zone between flowering and veraison can increase light penetration and can
improve flavour and aroma development in the fruit, however excessive exposure
can decrease sugar accumulation, malic acid and titratable acidity (Zoecklein et al.
1992
) and increase fruit susceptibility to sunburn, especially in warm climates. Leaf
removal can also result in an increase in fruit phenolic concentrations (Poni et al.
2004
) and depending on variety may lead to more bitter and astringent wines (Jack-
son and Jackson
2009
). The severity of the treatment and the methods employed to
remove the leaves (ie hand vs mechanised) contributes to the types of compounds
produced in the berry. This exemplifies that practises such as leaf removal need to
take into consideration the climate, the variety and the style of wine that is targeted.
Sugar Accumulation
While Brix is a measure of soluble solid concentrations it is not necessarily a good
indicator of sugar loading kinetics since berry volume can increase after rain or
shrink during later stages of ripening. Sugar loading into berries is dependent on
photosynthesis rates and the strength of competing sinks. Phloem derived sucrose
is unloaded via an apoplastic route requiring sucrose or hexose transporters (Fillion
et al.
1999
; Terrier et al.
2005
; Robinson and Davies
2000
) but the precise location
of these transporters is yet to be determined. After entering the cell, glucose and
fructose are stored in the vacuole. Rates of sugar accumulation are strongly depen-
dent on seasonal temperatures with global warming over recent years resulting in
more rapid ripening, leading to wines with higher alcohol content. Vine water status
is also crucial to berry sugar content since it controls stomatal conductance and this
has a direct effect on photosynthesis rates. Crop load is critical to berry ripening
since an insufficient leaf area results in a source limitation. Canopy architecture will
also have an influence on sugar accumulation since both leaf and berry temperatures
are influenced by exposure to the sun and wind.
Mineral Accumulation
Berries accumulate minerals in the skin, flesh and seeds. Potassium is the predomi-
nant mineral (approx 70 %), but phosphorus, calcium, sulphur and magnesium ac-
cumulation is also significant (Rogiers et al.
2006b
). The xylem mobile minerals
calcium, manganese and zinc accumulate prior to veraison while the phloem mo-
bile minerals potassium, phosphorus, sulphur, boron, iron and copper accumulate
