All About Pollen

Pollen and bees have been associated very closely throughout the years. The reason why there are actually mixed flower breeds is because bees continually move from one flowering plant to the next bringing pollen. The process of pollination is done primarily by bees, so it is important to know all about pollen so you can observe and understand how bees work and carry out their specific tasks. Learning about the process and pollen can help.

What is Pollen?

Pollen is described as a type of powder ranging anywhere from fine to coarse, which consists of pollen grains or microgametophytes. These produce the male sperm cells or gametes of seed plants. There is a hard coat that covers the pollen grain and protects the sperm cells during the movement process between the stamens of the flower to the pistil of the next available flowering plant. Single pollen grains are very small that you will need to magnify before you see the characteristics.

Pollen Structure

Every pollen grain has vegetative or non-reproductive cells and a generative or reproductive cell that contains two nuclei. The nuclei involve 1 tube nucleus and 1 generative nucleus. The group of cells is surrounded by a cell wall filled with cellulose called intine. There is a tough outer wall made of sporopollenin called exine.

Pollen is manufactured in the microsporangium found in the anther of a male cone of seed plants or coniferous plants or an angiosperm flower. Pollen grains appear in different shapes, surface markings and sizes. Pollen grains of firs, pines and spruces have wings. The smallest pollen grain is that of the plant called Forget-me-not, measuring only about 0.006 in diameter. There are wind-borne pollen grains that are huge as well. People studying pollen are called palynologists. The practice is very handy in paleontology, paleoecology and forensics.

More Pollen Details

The pollen walls functions to protect the sperm nucleus as the pollen grain moves from the anther to the stigma. It keeps the important genetic matter from solar radiation and drying out. The grain surface of the pollen is full of proteins and wax that are held together by sculpture elements on the grain surface. The outer wall of the pollen keeps the pollen grain from reducing in size and crushing the genetic matter in the desiccation process.

Structures of Pollen

The outer wall has two layeres called the tectum and the foot layer. The columella is the region, made of strengthening rods, separating the two layers. The pollen tube goes through the wall through apertures.

Pollen apertures are described as an alteration of the pollen grain wall. Some of the changes may include ridges, pores and thinning. As a result, the pollen grain may shrink or swell because of the alterations in moisture content. Furrows are called colpi and can be used to identify the different classes of pollen. The pollen may be classified via the furrows as either sulcate or colpate.

Pollination

Pollination is the popular process wherein pollen grains are transferred to the pistil or female reproductive structures in plants. The transfer can be done by the wind or by insects. If the transfer is done by the wind, the plant can be described as anemophilous. These types of plants create large quantities of very lightweight pollen grains, in some cases with air sacs. Transfers done by insects or bees are called entomophilous and produce pollen grains that are stick, heavy and full of protein. Insects and mites that feed on pollen are called palynivores.

More on Pollination

Among non-flowering plants, pollen germinates first in the pollen chamber found under and inside the micropyle. The pollen tube is created, thereby growing into the nucellus to create nutrients for developing sperm cells. Some sperm cells may be carried by the pollen tube or driven by their own flagella.

A pollen grain creates a pollen tube that moves down the tissue of the style into the ovary and is guided by hair projections along the placenta to the micropyle of an ovule. The nucleus of the tube cell is passed through the tube. The generative nucleus will divide to create 2 sperm cells. The tip of the pollen tube will be the destination of the sperm cells.