Soybean and Bees

Pollen
Pollen is a fine to coarse powder containing the microgametophytes of seed plants,
which produce the male gametes (sperm cells). Individual pollen grains are small enough
to require magnification to observe its structural details. Pollen grains have a hard coat
made of sporopollenin that protects the gametophytes during the process of their movement
from the stamens to the pistil of flowering plants or from the male cone to the female
cone of coniferous plants. If pollen lands on a compatible pistil or female cone, it
germinates, producing a pollen tube that transfers the sperm to the ovule containing the
female gametophyte (Twell, 2014).
Pollen itself is not the male gamete. Each pollen grain contains vegetative (non-reproductive)
cells (only a single cell in most flowering plants but several in other seed plants) and a
generative (reproductive) cell. In flowering plants, the vegetative tube cell produces the pollen
tube, and the generative cell divides to form the two sperm cells (Twell, 2014). Pollen
in plants is used for transferring haploid male genetic material from the anther of a single
flower to the stigma of another in cross-pollination. In a case of self-pollination, this process
takes place from the anther of a flower to the stigma of the same flower.
The pollen is produced in the microsporangium present in the anther of an angiosperm flower,
male cone of a coniferous plant, or male cone of other seed plants. Pollen grains come
in a wide variety of shapes (normally spherical), sizes, and surface markings, which are
characteristic of the species. Wind-borne pollen grains can be as large as about 90–100
µm (Pleasants et al., 2001).
In angiosperms, during initial flower development, the anther is composed of a mass of cells
that appear undifferentiated, except for a partially differentiated dermis. As the flower develops,
four groups of sporogenous cells form within the anther. The fertile sporogenous
cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac. Some
of the cells grow into nutritive cells that supply nutrition for the microspores that form by
meiotic division from the sporogenous cells (Twell, 2014).
In a process called microsporogenesis, four haploid microspores are produced from each
diploid sporogenous cell (microsporocyte, pollen mother cell or meiocyte), after meiotic division
(ALBERTSEN and PALMER, 1979). After the formation of the four microspores, which
are contained by callose walls, the development of the pollen grain walls begins. The callose
wall is broken down by an enzyme called callase and the freed pollen grains grow in size,
develop their characteristic shape, and form a resistant outer wall, called the exine, and an
inner wall, called the intine. The exine is what is preserved in the fossil record (Owen, 2014).
SoybeAn and bees
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