Biology Reference
In-Depth Information
nectary parenchyma photosynthetic pigments different from those of adja-
cent leaves.
If we consider recent research on these topics, it is clear that there have
been no conclusive studies on the sources of nectar components. Defoliation
or light deprivation experiments make it possible to determine the relative
contribution to nectar of recently produced photosynthates, as opposed to
stored assimilates. In
I. glandulifera
(Balsaminaceae), Búrquez and Corbet
(1998) used exclusion of nectar consumers and defoliation experiments to
determine that nectar carbohydrates have two sources: a part derived directly
from daily photosynthesis and another derived from stored carbohydrate
photosynthate. However, they do not say whether photosynthesis occurs in-
side or outside the flower, and also do not consider that photosynthetic parts
may be present in the flower or even in the nectary itself.
5
ECOPHYSIOLOGICAL SIGNIFICANCE
OF PARENCHYMA PLASTIDS
The nectary parenchyma may have amyloplasts or chloroplasts, containing
only a few stacks of grana and small starch granules, most probably involved
in low photosynthesis. This is the site where pre-nectar is transformed into
nectar and subsequently released outside. The subnectary parenchyma may
also contain chloroplasts or amyloplasts. Nectaries with amyloplasts in the
nectary and subnectary parenchyma cells seem less common than those with
chloroplasts. In addition, all extrafloral nectaries described ultrastructurally
have chloroplasts in their parenchyma (Pacini et al., 2003).
There are several papers on the ultrastructure of nectaries in which the
authors show chloroplasts, recognized by the presence of grana stacks and
plastoglobules. Chloroplasts may contain small or large starch grains
(Razem & Davis, 1999; Baum et al., 2001; Horner et al., 2003) or may even
be empty (Stpiczyńska & Matusiewicz, 2001; Stpiczyńska et al., 2003).
Nevertheless, the authors of these studies do not approach the problem of
whether nectar sucrose, or the other carbohydrates derived from chloroplast
photosynthesis are:
1.
Immediately conveyed to form nectar without being polymerized to
starch
2.
Polymerized to small starch grains to be hydrolysed later in the day
3.
Polymerized to form big starch grains hydrolysed during the night
