Agriculture Reference
In-Depth Information
bunches may cause the loss of berries, leaving an unsightly
spray of vascular strands (brush).
Each berry consists of a multi-layered pericarp and may
contain up to four seeds, although a number of cultivars for
fresh consumption are seedless. The cells of grape berries
are tightly packed with an internal gas volume of about
1.2 ml/100 g (Zosangliana & Narasimham 1993). The
pericarp can be divided into the exocarp (skin), mesocarp
(pulp) and endocarp. The pulp makes up most of the berry
weight and cells are highly vacuolated, containing high
levels of sugars and other soluble compounds (see below).
The seeds contain high levels of tannins (5-8%), oil
(10-20%) and phyto-hormones (Winkler
et al
. 1974). The
pericarp contains plastids throughout berry development
although their morphology changes at around anthesis and
lipid-like globules form within (Hardie
et al
. 1996).
Two layers can be distinguished in the exocarp or skin,
that is, the epidermis (6.5-10 μm) and the hypodermis
(107-246 μm) (Alleweldt
et al
. 1981). The mature
epidermis is covered with a cuticle about 3 μm thick which
includes an outer 0.5 μm wax layer (Casado & Heredia
2001) and contains stomata which by maturity are not
thought to be functional. Just after anthesis, the stomata
density was approximately 7±2 stomata per berry for the
cultivar Cabernet Sauvignon (Palliotti & Cartechini 2001).
The nonliving layers give the grape its 'bloom' which is an
important visual quality factor. The thickness and tough-
ness of the skin differ among varieties and can affect the
suitability of a cultivar for particular post-harvest uses
(Winkler
et al
. 1974). The thickness of the epidermal cell
walls is the only parameter showing a positive correlation
with resistance to physical stress (Considine 1981). Thus
the thickness and toughness of the skin contributes to the
resistance of grapes to handling injury. Furthermore, the
skin is the main location of the compounds that give
the grape its colour, aroma and flavour (see below)
(Winkler
et al
. 1974). Despite the stomata present in the
epidermis, cuticular transport is thought to be the main
route for water loss (Blanke & Leyhe 1987).
A recently described
in situ
fixation method, that better
preserves the membrane integrity, should allow new
information to emerge on the internal compartmentation of
grape berry cells (Diakou & Carde 2001).
period of very rapid cell division followed by marked cell
enlargement. Stage II, the lag phase is a period of slow
growth during which the embryos reach their final size,
chlorophyll starts to be lost and acidity reaches its highest
level. The start of stage III is called 'veraison' and is
marked by a rapid acceleration in growth, softening of the
berries, an increase in sugars and amino acids and the
activity of some enzymes and anthocyanin accumulation in
coloured cultivars. Acidity, chlorophyll and ammonia
levels and respiration rates all decrease during this stage.
The individual berries within a bunch do not ripen
synchronously (Coombe 1992). The variability that this
causes has constrained studies of the underlying biochem-
istry and has commercial implications for fruit quality at
harvest (Robinson & Davies 2000). Methods have been
developed to extract RNA from grape fruit at different
stages of development (Franke
et al
. 1995). Northern blot
analysis has shown that some genes are expressed only in
berries and only during ripening, whereas others are
expressed in a range of grape tissues but are up-regulated
during ripening. By homology with known genes, it
appears that these grape genes fall into two groups: those
that encode proteins involved in cell wall function and
structure and those whose products appear in plants under
applied stress (Davies & Robinson 2000). Further
understanding of the coordination of development at a
biochemical level will come as research continues into
changing gene expression (Robinson & Davies 2000). The
generation of Expressed Sequence Tags (ESTs) has been
the basis of microarray analyses (Waters
et al
. 2005; Terrier
et al
. 2005) that many teams are now using, and the
development of 'omics networks' (Grimplet
et al
. 2009;
Zamboni
et al
. 2010) will speed up research on genes,
proteins and metabolisms in the near future.
The recent characterisation of a fruit specific promoter
should further help the design of experiments targeted
towards study of berry ripening (Burger
et al
. 2006). Another
recent study dedicated to a mutation of grapevine leading to
fleshless berries will advance our understanding of the
genetic and developmental processes involved in the differ-
entiation of an ovary into a fruit (Fernandez
et al
. 2005).
Respiration and photosynthesis
The respiratory rate of the average single grape berry is
high early in stage I and then declines rapidly; it then
shows a rise at veraison (between stage 2 and 3), with more
CO
2
produced than O
2
consumed (Saulnier-Blache &
Bruzeau 1967). The rate of gross photosynthesis on a dry
weight basis peaks during the early part of stage I and then
declines rapidly; on a single berry basis it shows peaks in
Berry development
Pattern of development
Ollat
et al
. (2002) and Kanellis and Roubellakis-Angelakis
(1993) describe the division of the berry development into
three stages based on research by a number of researchers,
such as Alleweldt (1977) and Coombe (1992). Stage I is a
