Ampelology - Native Wine Grapes of Italy - page 6

were most often used to bolster ampelographic
information about varieties. Life is possible
because of biochemical reactions catalyzed by
enzymes (proteins composed of amino acid
chains), the structure of which is determined
by corresponding DNA sequences. Isoenzymes
are different molecular forms (in size or electric
charge) of enzymes that catalyze the same reac-
tions. Since they are correlated to known spe-
cifi c gene loci, they behave as genetic markers.
Isoenzymes can be differentiated by electro-
phoresis, which relies upon their different lev-
els of mobility within a gel to which an electric
current has been applied. The diverse positions
reached by the different isoenzymes are called
“profi les” or “patterns.” Four enzymatic sys-
tems may be used, but two are most reliable:
glucose phosphate isomerase (GPI) and phos-
phogluco mutase (PGM). Though useful, and
in fact much employed once, isoenzyme analy-
sis has limitations (Stavrakakis and Loukas
1983; Calò, Costacurta, Paludetti, Calò, Aru-
selsekar, and Parfi tt 1989). While grapes with
different isoenzyme patterns are certainly dif-
ferent varieties, it is not necessarily true that
those with similar patterns are the same vari-
ety. However, over time numerous cases of
synonyms and homonyms of grape varieties
have been apparently resolved with this method
(Calò, Costacurta, Cancellier, and Forti 1991;
Moriondo 1999).
We know grape-derived secondary metabo-
lites are the principal source of wine aroma,
fl avor, color, and taste and that they include
polyphenols (like anthocyanins and fl avonols)
as well as aromatic compounds (like monoter-
penes). Bate-Smith was the fi rst to show, in
1948, the role of phenolic pigments as genetic
markers, but Ribereau-Gayon was the fi rst to
apply them to grapevines, in 1953. Molecules
like geraniol and linalool were used to identify
grapes once. Unfortunately, concentrations of
these compounds can be affected by a number
of variables, including climate (Jackson and
Lombard 1993), water supply (Hardie and Mar-
tin 1990), and canopy management (Smart
and Robinson 1991). For example, wines made

from aromatic varieties are immediately recog-
nizable because of their spicy, fl oral, and very
fruity aromas: these are the result of aromatic
molecules such as terpenes, benzenoids, and
norisoprenoids. All grapes contain these mole-
cules in varying amounts, but grapes defi ned
as “aromatic” have more. Wines made with
Moscato varieties are especially rich in a ter-
pene called linalool, while members of the Mal-
vasia group have always been characterized by
another terpene, geraniol. The two molecules
are responsible for different aroma types, which
once were used to distinguish Moscato wines
from aromatic Malvasia wines: while linalool
leaves a sweet, musky impression typical of all
the Moscato s, geraniol recalls more refi ned
rose-like aromas, typical of all the aromatic
Malvasia s, white and red. For instance, Moscato
Rosa's aromatic profi le differs considerably
from that of Moscato Bianco, and is more simi-
lar to that of Brachetto or Malvasia di Casorzo.
For the same reason, Malvasia delle Lipari has
an aroma profi le that makes its wines more
reminiscent of some Moscato varieties than of
other Malvasia s. Unfortunately, though the aro-
matic expression of grapes is genetically prede-
termined, growing conditions and winemaking
techniques can easily alter the aromatic profi les
of wines to a signifi cant degree.

CELLULAR AND MOLECULAR BIOLOGY
TECHNIQUES

The genetic patrimony of each individual is
mainly constituted by DNA (deoxyribonucleic
acid) contained within the nucleus of cells,
though DNA is not found just in nuclei, but
also in other organelles within cells, such as
mitochondria. For DNA's content to be actually
useful, it needs to be copied and transported
outside the nucleus to other structures called
ribosomes, where its information is translated
and transformed into proteins. This task is per-
formed by two forms of RNA (ribonucleic acid):
messenger RNA (mRNA) and translator RNA
(tRNA). It is the mRNA that transports DNA
information to the ribosomes where the tRNA