Anthocyanin biosynthesis is strongly up-regulated in ripening
fruit of grapevines (Vitis vinifera L.) grown under
drought conditions.We investigated the effects of long-term
water deficit on the expression of genes coding for flavonoid
and anthocyanin biosynthetic enzymes and related transcription
factors, genes sensitive to endogenous [sugars,
abscisic acid (ABA)] and environmental (light) stimuli connected
to drought stress, and genes developmentally regulated
in ripening berries. Total anthocyanin content has
increased at harvest in water-stressed (WS) fruits by
37–57% in two consecutive years. At least 84% of the total
variation in anthocyanin content was explained by the
linear relationship between the integral of mRNA accumulation
of the specific anthocyanin biosynthetic gene UDPglucose
: flavonoid 3-O-glucosyltransferase (UFGT) and
metabolite content during time series from véraison
through ripening. Chalcone synthase (CHS2, CHS3) and
flavanone 3-hydroxylase (F3H) genes of the flavonoid
pathway showed high correlation as well. Genes coding
for flavonoid 3,5-hydroxylase (F35H) and O-methyltransferase
(OMT) were also up-regulated in berries from
dehydrated plants in which anthocyanin composition
enriched in more hydroxylated and more methoxylated
derivatives such as malvidin and peonidin, the grape anthocyanins
to which human gastric bilitranslocase displays the
highest affinity.The induction in WS plants of structural and
regulatory genes of the flavonoid pathway and of genes that
trigger brassinosteroid hormonal onset of maturation suggested
that the interrelationships between developmental
and environmental signalling pathways were magnified by
water deficit which actively promoted fruit maturation and,
in this context, anthocyanin biosynthesis.
Ke