LIBRO-CONGRESO-CITRUS

S06
environmental cues. From an evolutionary point of view, abscission is a highly favorable process that has
several advantages such as fruit and seed dispersal as well as the shedding of no longer needed, infected,
damaged or senescent organs. In an agricultural context, however, abscission is a major limiting factor for
crop productivity. In this regard, understanding the regulation of abscission is an important item for the citrus
fruit industry. Deeper understanding on the mechanisms underlying abscission would help to regulate crop
production and improve current cultural and management practices such as mechanical fruit harvesting or
removal of undesirable fruit production. In addition, further molecular research on abscission could help to
elucidate new molecular markers to improve genetic breeding. This review highlights the current status of
research on genes specifically associated with organ abscission that have been uncovered so far in citrus.
S06O04
Carbohydrate control over carotenoid build-up in citrus is conditional on fruit ontogeny
Fanciullino A.L. 1 , Poiroux-Gonord F. 1 , Poggi I. 1 , and Urban L. 2
1French National Institute for Agricultural Research (INRA), UR 1103 GEQA, France and 2Université d’Avignon et des Pays du Vaucluse
(UAPV), Laboratoire de Physiologie des Fruits et Légumes, France. fanciullino@corse.inra.fr
The final contents of primary and secondary metabolites of the ripe fruit depend on metabolic processes
which are tightly regulated during fruit ontogeny. Here, we hypothesized that the sensitivity of clementine
(Citrus clementina) fruit metabolism to carbohydrate supply was conditional on fruit developmental stage.
Defoliation or temporary shading were used as irreversible and reversible means, respectively, of obtaining
three levels of fruit load or leaf-to-fruit ratio. Treatments were applied at three key stages of fruit development:
early after cell division (S1), at color break (S2), and near maturity (S3). The highest fruit load obtained by
defoliation at S1 had the highest impact on fruit growth, maturity and metabolism, followed by the highest
fruit load obtained by shading at S1. Soluble sugars decreased by 18% in the first treatment, final fruit size by
21% and 18% in the irreversible and reversible treatments respectively, while organic acids increased by 46%
and 29%, respectively. Interestingly, total carotenoids increased by 50% and 18%, respectively. Changes in leaf
starch content and photosynthesis supported that these early treatments triggered a carbon starvation in the
young fruits, with irreversible effects. Furthermore, our observations on the early treatments challenge the
common view that carbohydrate supply influences positively carotenoid accumulation in fruits. We propose
that early carbon starvation irreversibly promotes carotenoid accumulation.
S06O05
Largely altered terpenoids production in red-fleshed fruits of ‘Cara Cara’ navel orange (Citrus
sinensis L. Osbeck) in comparison with pale-fleshed Seike navel orange
Xu J., He M., Liu X., Gao H.J., Wang Z., Deng X.X., Cheng Y.J., and Zhang H.Y.
Key Laboratory of Horticultural Plant Biology, Ministry of Education (HZAU), Postharvest and fruit quality, China.
xujuan@mail.hzau.edu.cn
For two growing seasons, the synthesis of carotenoids, limonoids and abscisic acid were investigated in fruits
of red-fleshed ‘Cara Cara’ and pale-fleshed Seike navel oranges (Citrus sinensis). ‘Cara Cara’ accumulated
large amount of phytoene, phytofluene, lycopene and thus total carotenoids in its flesh, while β-carotenoids
were dominant in flesh of ‘Seike’ navel orange. Real time-PCR analysis revealed that lycopene accumulation
in the juice sacs of ‘Cara Cara’ was more likely attributed to the up-regulated expression of phytoene synthase
gene than the expression level of lycopene cyclase genes. However, the lack or the decrease of lycopene in
leaves and fruit flavedo implied the different regulation mechanism in different tissues. In comparison with
‘Seike’, throughout the fruit development, ‘Cara Cara’ contained lower contents of abscisic acid and higher
contents of limonin and nomilin in its juice sacs. Additionally, contents of other compounds such as naringin
(the main bitter flavonoids in the citrus), soluble sugars and organic acids were found significantly different
between two oranges for both seasons. Furthermore, RNA-seq and bioinformatics’ analysis declared the
global differences in the processes of carotenoids biosynthesis, starch and sucrose metabolism, citrate cycle
and glycolysis pathways between the two navel oranges.
96 - VALENCIA CONFERENCE CENTER, 18th-23rd NOVEMBER 2012