Biology Reference
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et al., 1996). After measuring the volume flux of the floral nectar of
Digitalis
purpurea
(Scrophulariaceae) through individual stomatal apertures, Gaffal
et al. (1998) concluded that only a fraction of the total number of stomata per
nectary would be sufficient to release the amount of nectar produced. In
Hedera helix
(Araliaceae; Vezza et al., 2006) and
Echinacea purpurea
(Asteraceae; Wist & Davis, 2006) closed immature stomata were present on
the surface of the nectary during the secretion phase.
The stomatal apertures are continuous with intercellular spaces of the
nectary parenchyma (Gaffal et al., 1998) and there is evidence to suggest
that modified stomata are unable to closely regulate nectar flow through
them (Davis & Gunning, 1993; Razem & Davis 1999). For instance, asyn-
chrony in stomatal development (pores wide open a few days before the start
of nectar secretion and after secretion has ceased) suggests little coordination
between pore opening and nectar release (Davis & Gunning, 1992; Davis,
1997; Razem & Davis, 1999). According to Teuber et al. (1980) and Davis
and Gunning (1993), leaf and nectary stomata differ in their response to
various stimuli. Nectary stomata remained open under all treatment condi-
tions, suggesting that nectary stomata lack the turgor- and ion-mediated
movements generally found in leaf stomata.
Figure 4.
Nectary stomata of
Cucurbita pepo
male flower before (
left
) and after (
right
) nectar
secretion. The inner portion of guard cells (gc), where the outer cuticular ledge (cl) is evident
before nectar secretion (A), is collapsed at the end of secretion (B). Bar = 50 µm.
