Soybean and Bees

with protection activity, as well as on Acacia EFN and pollination droplets of gymnosperms
(Carter and Thornburg, 2004; Gonzales-Teuber et al., 2009a, 2010; Wagner
et al., 2007; Carter et al., 2007; WENZLER et al., 2008; WOLF et al., 1981).
On investigating nectar composition, Heil et al. (2005) and Kram et al. (2008) found some
enzymes that play a central role in the post secretory tailoring of nectar chemistry. Kessler
and Baldwin (2007) identified nectar odors eliciting pollinator behavior. Radhika et al. (2010)
associated the hormone jasmonic acid (JA) with the modulation of the secretion of FN, while
Heil et al. (2001), Heil (2004) and Heil et al. (2004) reached the same conclusion regarding
EFN.
Three genes encoding for putative transcriptions factors have been established to be involved
in nectary development: CRABS CLAW (CRC), and BLADE-ON-PETIOLE 1 and 2 (Bowman
and Smyth, 1999; McKim et al., 2008). Afterwards, Ruhlman et al. (2010) discovered a
gene encoding an apoplastic invertase in Arabidopsis thaliana, whose function is required for
FN secretion. The first proteomes obtained from the nectars of various species were mentioned
by Gonzales-Teuber et al. (2010), Park and Tornburg (2009), Peumans et al. (1997) and
Hillwig et al. (2010).
Two alternative and nonexclusive scenarios were mentioned by Heil (2011), regarding the
origins of carbohydrates, the major class of nectar components: (i) direct transport from the
phloem; and (ii) accumulation of starch in the developing nectary and its hydrolysis during
active secretion. Alternatively, some carbohydrates might even derive from in situ photosynthesis.
The direct secretion of the products of the current assimilation process has been
shown repeatedly for FN, using the girdling of flower shoots as well as darkening and defoliation
experiments (Gaffal et al., 2007; von Czamowski, 1952). Radhika et al. (2008) used 13 C
labelled CO 2
to demonstrate that EFN also contains sugars that have been assimilated during
the last hours before secretion.
The second scenario is supported by studies of Horner et al. (2007) and Ren et al. (2007),
showing that nectaries of ornamental tobacco and Arabidopsis accumulate large quantities
of starch. The degradation of this starch into mono and disaccharides coincides with the onset
of nectar secretion during anthesis. A breakdown of accumulated starch, as well as programmed
cell death during and after secretion, have also been described for further, taxonomically
unrelated species such as soybean (Glycine max) (Horner et al., 2003) and common
fox-glove (Digitalis purpurea) (Gaffal, 2007; Baker and Baker, 1975). According to Pacini et
al. (2003), many species possess amyloplasts in their nectary tissue that can become directly
connected to the vacuole and consecutively emptied during the phase of most active FN secretion
(Gaffal et al., 2007).
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