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Ligaria cuneifolia (Loranthaceae; Rivera et al., 1996), Mandevilla pentlandiana
(Apocynaceae; Torres & Galetto, 1998), and Platanthera chlorantha (Orchi-
daceae; Stpiczyńska, 2003a, b). These examples concern species with
exposed nectar ( C. carvi , Eucalyptus ), species with hidden nectar ( C. pepo ,
C. maxima , A. castanea ), and species with nectar stored in a spur ( P. chlor-
antha , A. verdickii , L. vulgaris ).
It is now evident that secretion may occur concomitantly with reabsorp-
tion and that sometimes reabsorption continues after secretion has ended
(Bielesky & Redgwell, 1980; Búrquez & Corbet, 1991; Nicolson, 1995;
Nepi et al., 2001; Corbet, 2003).
Reabsorption of unconsumed nectar seems quite a common phenomenon,
especially when the nectary is large in volume and the quantity of produced
nectar is not negligible. This process is more difficult to explain when the
nectary is persistent and contains chloroplasts, because these organelles con-
tinue their anabolic activity and cannot store material coming out of a cell.
Reabsorbed substances are not temporarily stored in chloroplasts and must
be immediately transported into other parts of the flower or plant.
Two main functions of nectar reabsorption can be recognized: recovery
of resources invested in nectar production and a homeostatic mechanism
during nectar secretion and presentation (Table 1). The two functions may
not be mutually exclusive in a given species: in C. pepo, nectar reabsorption
has a homeostatic function during flower anthesis and subsequently a re-
source recovery function after flower closure (Nepi et al., unpublished data).
Nectar production requires considerable expenditure of energy. Pyke
(1991) reported that removal of nectar from flowers of Blandfordia nobilis
(Blandfordiaceae) increased net nectar production but reduced the plant's
ability to produce seeds, which can result in reduction of plant growth and
reproduction during the following season. Resource recovery is therefore an
important reason why plants try to re-utilize this source of carbohydrates not
collected by pollinators. This strategy of resource recovery has recently been
demonstrated or postulated in several species (Búrquez & Corbet, 1991;
Koopowitz & Marchant, 1998; Luyt & Johnson, 2002; Stpiczyńska, 2003a, b).
In species such as C. pepo and P. chlorantha , all unconsumed nectar is re-
claimed regardless of pollination, maximizing the recovery of energy
invested in nectar production (Nepi & Stpiczyńska, 2007). In some plant
species nectar reabsorption is evidently induced by pollination. In the
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