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mainly maintained by very high production of dilute nectar throughout an-
thesis (Nicolson & Nepi, 2005).
On the other hand, the capacity to vary sugar concentration may be an
adaptive character to ensure visits by a wider spectrum of pollinators, as in
the case of Catalpa speciosa (Bignoniaceae; Cruden et al., 1983). Moreover,
if a pollinator does not remove nectar, reabsorption may be a form of com-
pensation for nectar theft. In M. venosum , nectar reabsorption at night
followed a decline in pollinator activity (Luyt & Johnson, 2002). Nectar re-
absorption may also reduce the negative effects of post-pollination visits,
which have the potential to damage already pollinated flowers (Burqúez &
Corbet, 1991).
Whereas several papers tackle the cyto-physiological mechanism of nec-
tar production and secretion (see “Nectar secretion mechanism and models
of nectary function” on page 168), very few consider nectar reabsorption
(Nepi et al., 1996a; Nepi and Stpiczyńska, 2006). Nectar is generally reab-
sorbed by the nectary itself and according to Búrquez and Corbet (1991) this
is why some plants that accumulate nectar in spurs or other types of reser-
voirs do not reabsorb nectar. However, reabsorption takes place in L. Vulgaris
(Nepi et al., 2003), in which nectar flows from the nectary to the spur.
Nectar is not reabsorbed by all plants in which nectar remains in contact
with the nectary. According to Búrquez and Corbet (1991), reabsorption
seems to occur mainly in flowers whose nectaries remain attached to the
plant after the corolla has fallen, or when the fall is delayed or the corolla
wilts.
Epidermal cells are most involved in nectar reabsorption (Nepi et al.,
1996a). Nectary stomata, from which nectar often exudes, do not seem to be
involved in the process (Nepi & Stpiczyńska, 2007). Transport of reabsorbed
nectar sugars from the epidermis to parenchyma cells may occur via apoplast
or symplast (Nepi & Stpiczyńska, 2007) and reabsorbed sugars may be
stored temporarily as starch grains in amyloplasts (Nepi et al., 1996a; Wist
& Davis, 2006). Reabsorbed sugars from a flower nectary are mainly trans-
located to the nearest developing ovule or ovary (Nepi & Stpiczyńska,
2007). They may go even longer distances—in P. chlorantha , reabsorbed
sugars seem to be utilized in the whole inflorescence, which has flowers at
different stages of development; they can be translocated upward or down-
ward as far as 12.5 cm towards growing ovaries (Nepi & Stpiczyńska, 2007).
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