Biology Reference
In-Depth Information
An increase in total secretion after nectar removal can be explained by
the fact that nectar secretion stops after a maximum is reached and nectar
production can only be re-activated after nectar removal. This is probably
related to the necessity for several pollinator visits to deposit enough pollen
on the stigma. Alternatively, increased total nectar production in repeatedly
sampled flowers is considered to be evidence that nectar secretion proceeds
in conjunction with nectar reabsorption: the effect of reabsorption is reduced
by sampling a flower repeatedly at short intervals, minimizing the quantity
of nectar available in the flower for reabsorption (Corbet, 2003).
3.1
Nectar reabsorption: resource recovery
and homeostasis
Búrquez and Corbet (1991) proposed a model to explain changes in the ap-
parent secretion rate, defined as the rate of change of solute content of nectar
in undisturbed, unvisited flowers. The apparent secretion rate can be resolved
into two components: gross secretion rate (rate of change of solute content in
nectar of repeatedly sampled flowers) and apparent reabsorption rate. In fact,
for some species there is evidence that reabsorption of nectar proceeds in
conjunction with secretion (Búrquez & Corbet, 1991; Nicolson, 1995; Corbet,
2003) so that the quantity of nectar present in a bagged flower at a given
time is a function of the relative rates of secretion and reabsorption.
Since Bonnier's (1879) finding that flowers of
Platanthera
(Orchidaceae)
reabsorb nectar, several direct and indirect demonstrations of nectar reabsorp-
tion have been published (Table 1). Nectar reabsorption is not an unusual
floral feature. It is reported in many plant species and occurs irrespective of
the age or sexual expression of the flower, and does not depend on pollina-
tion. Also, reabsorption of nectar occurs regardless of nectary structure and
the manner of nectar exudation via modified stomata or unicellular hairs.
Burqúez and Corbet (1991) reported nectar reabsorption in
Brassica napus
by net solute loss in unvisited flowers. Masierowska and Stpiczyńska (2005)
demonstrated nectar reabsorption in
Sinapis alba
, another species of Brassi-
caceae. Reabsorption of uncollected nectar has been noted in
C. pepo
and
C. maxima
(Cucurbitaceae; Nepi et al., 1996a, b, 2001; Ashworth & Galetto,
2002),
Eucalyptus
sp. (Myrtaceae; Davis, 1997),
Aerangis verdickii
(Orchi-
daceae; Koopowitz & Marchant, 1998),
Mystacidium venosum
(Orchidaceae;
Luyt & Johnson, 2002),
Linaria vulgaris
(Scrophulariaceae; Nepi et al.,
2003), and
Aloe castanea
(Asphodelaceae; Nicolson & Nepi, 2005). Nectar
is also reabsorbed in
C. carvi
, after each male and female flower stage
(Apiaceae; Langenberger & Davis, 2002), and near the end of the flower
lifetime in
Combretum fruticosum
(Combretaceae; Bernardello et al., 1994),
