Biology Reference
In-Depth Information
polysaccharides, but do not show the blue colour of the IKI test, i.e., the
typical reaction for starch (Nepi et al., 1996a). Afterwards these plastids
empty and the carbohydrates are probably totally reabsorbed by contiguous
parts of the flowers. The nectary then abscisses. In this case it seems that
empty amyloplasts are important as storage sites during the reabsorbing
process.
This pattern of nectary plastid development (from proplastids to amy-
loplasts) could be more common in the tropics, where more animals are
active at night, than in temperate zones. No research has been done into
these aspects. Degeneration of nectaries with amyloplasts at the end of secre-
tion or after nectar reabsorption seems to be a general feature. In Aloe and
Gasteria , which have septal nectaries, dedifferentiation of amyloplasts to
chloroplasts is recorded (Schnepf & Pross, 1976; Nepi et al., 2006). This
dedifferentiation enables transformation of nectary parenchyma into fruit
parenchyma.
Research on plastid development mainly concerns floral nectaries. As far
as is known extrafloral nectary parenchyma cells have only chloroplasts
(Table 4). The presence of chloroplasts in extrafloral nectaries allows pro-
duction of low quantities of nectar over long periods: several weeks to
months, like the age of the leaf where they are situated. This nectar is con-
sumed by ants that protect the plant from predators. Floral nectaries differ
widely according to the dynamics of nectar production and plastid differen-
tiation patterns, because they are visited by a wider spectrum of consumers
and may reabsorb unconsumed nectar (Table 4).
6
NECTAR PRESENTATION
6.1
Floral nectaries
Fahn (1979a) recognized three different positions of floral nectaries with
respect to the organ bearing them:
At surface level
Forming an outgrowth, as in Brassicaceae and Fabaceae
Sunken, as in the ovary septal nectaries of monocots
These different positions influence the structure of the nectary and
its persistence, the manner of nectar secretion, nectar presentation, and the
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