Soybean and Bees

In the microgametogenesis, the unicellular microspores undergoes mitosis and develops into
mature microgametophytes containing the gametes. In some flowering plants, germination
of the pollen grain often begins before it leaves the microsporangium, with the generative
cell forming the two sperm cells. The exine often bears spines or warts, or it is sculptured
following various patterns, and the character of its markings is of value on Taxonomy for
identifying genus, species, or even a cultivar. The spines may be less than a micron in length
referred to as spinulose (scabrate), or longer than a micron referred to as echinate. Various
terms also describe the sculpturing such as reticulate, a net like appearance consisting of
elements separated from each other by a lumen (Owen, 2014).
The pollen grain surface is covered with waxes and proteins, which are held in place by
structures called sculpture elements present on the surface of the grain. According to Owen
(2014), the outer pollen wall is composed of two layers, which prevents the pollen grain from
shrinking and crushing the genetic material during desiccation. These two layers are the
tectum and the foot layer, which is just above the intine. The tectum and foot layer are separated
by a region called the columella, which is composed of strengthening rods. The outer
wall is constructed with a resistant biopolymer called sporopollenin. While the pollen grain
is moving from the anther to the stigma, the pollen wall protects the sperm from drying out
and against solar radiation.
The pollen tube passes through the pollen grain wall by way of structures called apertures
(Owen, 2014). The apertures are various modifications of the wall of the pollen grain that
may involve thinning, ridges and pores. They allow shrinking and swelling of the grain
caused by changes in moisture content.
On studying pollinators, specially their habits and preferences, it is paramount to identify
the pollen form different sources. They normally can be differentiated by its physical appearance.
According to Owen (2014), elongated apertures or furrows in the pollen grain are
called colpi or sulci, while apertures that are more circular are called pores. Pollen may be
referred to as inaperturate (apertures absent) or aperturate (apertures present). The aperture
may have a lid (operculum), hence is described as operculate. The orientation of furrows
(relative to the original tetrad of microspores) classifies the pollen as sulcate or colpate. Sulcate
pollen has a furrow across the middle of what was the outer face when the pollen grain
was in its tetrad. If the pollen has only a single sulcus, it is described as monosulcate. Colpate
pollen has furrows other than across the middle of the outer faces. Eudicots have pollen with
three colpi (tricolpate) or with shapes that are evolutionarily derived from tricolpate pollen.
The evolutionary trend in plants has happened from monosulcate to polycolpate or polyporate
pollen.
32 SoybeAn and bees