Soybean and Bees

legume nectaries. Species involved on more recent studies are Lotus corniculatus (Murrell et
al., 1982; Teuber et al., 1980), Phaseolus vulgaris (Webster et al., 1982), Pisum sativum (Razem
and Davis, 1999), Trifolium pratense (Picklum, 1954; Eriksson 1977) and Vicia faba (Waddle
and Lersten, 1973; Davis et al., 1988; Davis and Gunning, 1991, 1992, 1993; Stpiczynska,
1995). Authors that have investigated soybeans nectaries, its structure and functionality
are Purseglove (1968), Carlson (1973), Waddle and Lersten (1973), McGregor (1976), Erickson
and Garment (1979), Carlson and Lersten (1987), Crozier and Thomas (1993) and Horner
et al. (2003).
The study from Horner et al. (2003) details changes occurring inside the cells and tissues of
the nectary, the subtending floral receptacle, the vasculature that innervates the nectary,
and the adjacent gynoecium glandular trichomes. They demonstrated that soybean nectaries
have a different ultrastructure and method of secretion (holocrine), not previously reported
for any other legume. The soybean nectary undergoes programmed cell death and ceases
to exist much beyond the pollination stage. These data serve as a foundation for observing
nectaries in the wild annual soybean Glycine soja and the wild perennial Glycine species where
cross-pollination and nectar output are greater than the cultivated G. max (Brown et al.,
1986; Schoen and Brown, 1991; Fujita et al., 1997). The structure of the floral nectaries on
soybeans develop between the bases of the central gynoecium and lateral stamen ring. They
have a discoid shape, being formed immediately before flower opening.
A nectary consists of thin-walled parenchyma cells, showing dense cytoplasm and a nucleus,
Golgi bodies and vesicles, mitochondria, plastids, endoplasmic reticulum, many ribosomes,
and one or more vacuoles. The fingers of phloem penetrate the nectary at its base. They
are composed of sieve tubes and companion cells, both with very small wall ingrowths and
thought to provide sugars (Horner et al., 2003), being originated from 10 vascular bundles
with xylem, which innervate the stamen ring peripheral to the nectary. The flower receptacle,
just below the base of the nectary, gynoecium, stamen ring, and more peripheral petals
and sepals, displays the main vascular bundle and its branches that innervate all of these
flower organs. Surrounding these basal vascular bundles there is a connective tissue that
contains many calcium oxalate crystals.
Besides sugars, other substances are likely to be found on nectar (Griebel and Hess, 1940;
Vogel, 1969; Baker and Baker, 1973, 1975, 1983; Deinzer et al., 1977; Rodriguez-Arce
and Diaz, 1992; Roshchina and Roshchina, 1993; Ecroyd et al., 1995; Ferreres et al.,
1996; Cabras et al., 1999; Petanidou et al., 2000; kapyla, 1978). Variation in the ratio of
xylem and phloem in vasculature of the nectary seems to affect carbohydrate composition
(Frei, 1955; Frey-Wyssling, 1955; Esau, 1965; CONRAD and PALMER, 1976). Attractiveness
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