Biology Reference
In-Depth Information
When nectary parenchyma has chloroplasts, there are two possibilities at
the end of secretion: the nectary either abscisses or persists. Abscission
occurs if the nectary is a small inconspicuous protuberance, as in many
members of Brassicaceae, Fabaceae, and Asteraceae (Horner et al., 2003).
Persistence means that photosynthesis by the nectary parenchyma continues,
though products of photosynthesis are shifted to benefit the developing fruit.
This calls for a rearrangement in the manner of conveying parenchyma pho-
tosynthate, i.e., a reorientation of cell polarity and flux must occur in phloem
cells. Table 6 presents some examples of modes of nectar secretion, nectar
reabsorption, and nectary and nectar fates.
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VARIABILITY OF NECTAR CHARACTERISTICS
The physicochemical characteristics of nectar vary with biotic and abiotic
parameters. In general, the longer the flowering period of a species, the
wider the variations in nectar physicochemical properties (Nepi et al., 2003).
Similarly, the longer the period of flower anthesis, the wider the variations in
nectar properties (Vesprini et al., 1999).
There is a mass of literature demonstrating interspecies variability of nec-
tar properties in terms of volume, solute concentration (and thus total sugar
production), and composition. These differences have been interpreted as
adaptive: pollinator behaviour favours certain traits over others (Faegri &
van der Pijl, 1979; Baker & Baker, 1983a; Cruden et al., 1983; Cnaani et al.,
2006). Differences in nectar volume are explained on the basis of a cost-
benefit balance: plants are most fit when they produce the lowest volume of
nectar that will attract their pollinator (Lanza et al., 1995 and references
therein). In this respect, species pollinated by large animals such as birds and
bats produce more nectar than species pollinated by smaller animals such as
bees, bumblebees, butterflies, and moths (Baker & Baker, 1983a). Differ-
ences in nectar concentration are interpreted as a balance between different
factors: pollinator preference for high concentration, pollinator difficulty in
handling viscous solutions and plant energy allocation patterns that minimize
the cost of nectar production (Baker and Baker, 1983a, Zimmerman, 1990).
Differences in composition are attributed to pollinator preferences linked
also to alternative sources of food (Baker & Baker, 1983a, 1986).
