Biology Reference
In-Depth Information
Davis et al., 1988),
Digitalis purpurea
(Scrophulariaceae; Gaffal et al., 1998),
and
Cyclanthera pedata
(Cucurbitaceae; Pacini et al., 2003). Phloem and
xylem are present in
Capparis retusa
(Brassicaceae; Di Sapio et al., 2001),
Ecballium elaterium
(Cucurbitaceae; Fahn & Shimony, 2001),
Solanum
stramonifolium
(Solanaceae; Falcão et al., 2003), and
Hexisea imbricata
(Orchidaceae; Stpiczyńska et al., 2005a) (see also the examples reported by
Fahn (2000) and Nepi (2007)).
Only phloem is present in the extrafloral stipular nectaries of
Passiflora
sp.
(Passifloraceae; Durkee, 1982) and
Sambucus nigra
(Caprifoliaceae; Fahn,
1987). Both phloem and xylem are present in those of
R. communis
(Eu-
phorbiaceae; Baker et al., 1978),
Euphorbia neriifolia
(Euphorbiaceae;
Arumugasamy et al., 1990), and
V. faba
(Fabaceae; Davis et al., 1988) .
No definitive conclusions can be drawn from the site of origin of the nec-
tar components; however, nectary parenchyma is certainly the site where
these components are transformed into nectar, and nectar carbohydrates are
undoubtedly unloaded from the phloem or partly produced by chloroplasts of
the subnectary parenchyma cells.
There are several reasons why nectar components may have different
anatomical and histological origins:
•
Location of nectaries in different parts of the flower
•
Production of nectar for different types of consumers, with different com-
positions
•
The environment in which the plant grows
•
Time of flowering during the year
•
Time of exposure of the nectary during the day
Table 2 shows the different components of nectar and their probable origins
and functions.
It is reasonable to believe that the more the nectary is exposed to
sunlight, the higher the contribution of nectary photosynthesizing paren-
chyma to nectar carbohydrates. In Araliaceae and Apiaceae, nectaries are
located in the upper part of the ovary (Bernardello, 2007, p. 83). Vezza et al.
(2006) studied the nectary biology of ivy (
Hedera helix
, Araliaceae), which
has an exposed nectary, and demonstrated that photosynthetic pigments in the
nectary and in leaves adjacent to the inflorescence are qualitatively similar
but quantitatively diffferent: leaves contain a larger amount of photosynthetic
