Biology Reference
In-Depth Information
affected by the intensity of herbivory (Wäckers et al., 2001; Mondor & Ad-
dicott, 2003) and that herbivore-induced plant volatiles are responsible for
increased extrafloral nectar production (Choh et al., 2006; Kost & Heil,
2006).
According to Elias (1983), who modified the early classification of
Zimmermann (1932), seven morphological types of extrafloral nectary can
be observed: formless nectaries, flat nectaries, elevated nectaries, scale-like
nectaries, hollow nectaries, pit nectaries, and embedded nectaries. They are
usually small protuberances, which may be covered by protecting non-
secretory hairs (Sousa e Paiva et al., 2001; Falcão et al., 2003). Different
morphological types of extrafloral nectaries may co-occur in different posi-
tions even on the same leaf of a plant such as
Passiflora
sp. (Galetto &
Bernardello, 1992; Blüthgen & Reifenrath, 2003). Two types of extrafloral
nectaries—differing in morphology, anatomy, function, and nectar compo-
sition—were described in
Vigna unguiculata
by Pate et al. (1985). Four
extrafloral nectary sites (petiole, calyx, corolla, fruit) can be recognized in
Campsis
(Bignoniaceae), which also has floral nectaries (Elias & Gelband,
1976).
As happens among floral nectaries, some extrafloral nectaries are also
devoid of vascularization and lack the anatomical organization typical of
nectaries. Elias (1983) described this type of nectary as non-vascularized,
non-structural; examples are those located in the outer verticel of petals in
certain Bromeliaceae, Zingiberaceae, Paeoniaceae, and Cactaceae (Galetto &
Bernardello, 1992 and references therein). More frequently, extrafloral nec-
taries have a structure not very different from that of floral nectaries. The
most frequent vascularization consists of phloem or phloem and xylem. A
continuous thick cuticle covers the epidermal cells of the extrafloral nectar-
ies and nectar release generally takes place through cuticle rupture. In some
cases, such as in some Bromeliaceae species (Galetto & Bernardello, 1992)
and
Solanum stramonifolium
(Solanaceae) (Falcão et al., 2003), nectar can
be secreted through stomata. Secretory cells located under the epidermis may
occur in one or several layers and are usually elongated and orientated along
a vertical axis. Plastids in extrafloral nectaries are generally chloro-amylo-
plasts (Pacini et al., 2003, see also Table 1) with very few starch grains. In
fact, extrafloral nectaries show less evident starch formation and degradation
processes than floral nectaries (Durkee et al., 1981).
Extrafloral nectaries also generally have merocrine secretion, though
holocrine secretion has been described for
Ailanthus glandulosa
(Clair-Mac-
zulajtys & Bory, 1983). Holocrine secretion has also been reported in the
