Agriculture Reference
In-Depth Information
FLOWERIN LOCUS C
(
FLC
) gene encodes a domain protein that represses
flowering. Elevated levels of
FLC
expression may be responsible for reductions in
FT
activity. It has been hypothesized that floral repressors ensure the correct repro-
ductive timing by controlling promoters, and, in some cases, reducing its expression
to facilitate the action of promoters, thereby contributing to flowering induction.
The determination of floral identity, i.e. bud differentiation, is linked to
APETALA1
(
CsAP1
) and
LEAFY
(
CsLFY
) genes.
FLOWERING LOCUS D
(
FD
) encodes a protein required for
FT
function, and
takes part in the specific signalling pathways that occur at the shoot apex. In
Cit-
rus
,
FD
expression in buds was markedly higher than in leaves in both November
and February (NH). As for other species, this observation reinforces the hypothesis
that its role in
Citrus
is decisive at the apical level, possibly because the transition
from vegetative to floral meristem mainly occurs there. In fact, this gene has been
described as a strong modulator of
FT
action specifically in the meristem. Hence,
promoter genes, such as
FT
and/or
FD
, together with the reduction in the suppressive
action of inhibitor genes (
FLC
), and with the expression of
CsAP1
and
CsLFY
iden-
tity genes, probably contribute to the development of floral morphogenesis in
Citrus
.
Fruit, low temperature and water stress have been related to floral bud induction.
See Agustí (
2003
), Agustí and Almela (
1991
), Chica and Albrigo (
2013
), El-Otmani
(
2006
), El-Otmani et al. (
2000
), Muñoz-Fambuena et al. (
2011
;
2012
), Nishikawa
et al. (
2007
), Spiegel-Roy and Goldschmidt (
1996
) for further information.
Fruit Development and Ripening
Fruit Set
Fruit set is defined as the transition of the quiescent ovary of the flower to developing
fruit. The process requires the reactivation of cell division in the ovary, and it is
regulated by external and, mainly, internal factors. If ovary growth is not reacti-
vated or if it is arrested during early fruitlet development the abscission process is
triggered and fruit set is not accomplished. For further information see reviews by
Agustí (
2003
), El-Otmani (
2006
), El-Otmani et al. (
2000
), and Spiegel-Roy and
Goldschmidt (
1996
).
In
Citrus
seeded varieties, in which pollination and fertilization are absolutely
necessary for fruit set, ovary growth of un-pollinated flowers is observed in the first
2 weeks following anthesis; thereafter, a rapid 100 % ovary abscission is produced.
But the anatomical changes in the ovary occur in the same way, and at the same
time, in un-pollinated or cross-pollinated flowers during the first days following an-
thesis, which reflects an uncoupling of the fertilization and fruiting time processes.
Thus, ovary growth at the onset of the cell division stage is independent of pollina-
tion, and the ability to set fruits in seeded varieties should be inevitably associated
with the stimuli produced by gibberellins in developing seeds. This is the case of
some sweet orange cultivars.
