Pollen in Forensic Science

"A mass of microspores in a seed plant."
Pollen

Introduction

To fertilize other plants of the same species, trees, flowers, grasses, and weeds generate pollen, a very fine powder.

Pollen Structure

The majority of pollen grains have three unique components. The nuclei needed for fertilization are found in the central cytoplasm. The inner layer, known as the intine, and the outer layer, known as the exine, are the other components that make up the wall of the grain. The intine partly contains cellulose or hemicellulose.

Pollen Formation

The formation of pollen is a complicated process. The male element of flowering plants is the stamen. This is composed of a single stalk-like filament and an anther. The pollen sacs, which produce the pollen grains, are frequently seen in the anther. Two male gametes are contained in a single cell that makes up each pollen grain. Anthers split open and release pollen when they are fully developed. Both male gametes participate in fertilization, which results in the development of a zygote and endosperm. The only plants that undergo this repeated fertilization process are flowering plants.

Pollination

Pollination is the transportation of pollen grains from an anther to a stigma on the same flower or another flower. Self-pollination and cross-pollination are the two types of pollination.

Self-Pollination

When pollen grains are transported from anthers to stigmas on the same flower or an adjacent flower on the same plant, self-pollination takes place.

Cross-Pollination

When pollen grains are deposited on the stigma of another plant within the same species, cross-pollination takes place.

Classification of Pollen

Classification of pollen is based on structural characteristics.

The size, shape, aperture count, and surface roughness of pollen grains vary remarkably.

These distinguishing traits allow a plant to be identified and classified at the family, genus, and, in some cases, species levels.

The following properties are useful in identifying pollen types:

1. size

2. shape

3. number of apertures

4. surface texture

Size

Pollen grains are measured in micrometers µm (also known as microns).

Pollen grains exhibit a wide range in size. Most pollen grains have a diameter of 10 to 70 µm. There could be thousands of individual grains in just a small amount of pollen.

Shape

The majority of pollen grains have a sphere, an ovoid, a triangle, or a disc shape. These fundamental geometric concepts have several variations, including elongated and flattened.

Apertures

Male gametes escape through openings in the pollen grain wall during pollination which is known as Apertures. There are two distinguishable types: colpi, which resemble elongated furrows, and pores, which have a round shape. A pollen grain may have multiple apertures, and pores and colpi may occasionally coexist.

Surface texture

Pollen species are highly diverse in terms of their outward appearance. The exterior wall (exine), which varies greatly between species, is frequently flamboyantly carved. Between pollen grain and stigma, it is believed to play a significant part in species-specific recognition mechanisms that aid in germination.

Palynology

The study of plants’ pollen, spores, and particular microscopic plankton species, collectively referred to as palynomorphs, both in their lives and fossil forms is known as palynology.

Hyde and Williams initially used the term “palynology” in the Pollen Analysis Circular in 1944 (one of the first journals devoted to pollen analysis, produced by Paul Sears in North America), with Swedish geologist Ernst Antevs.

Indian palynologist Parameswaran Krishnan Kutty Nair (1930- 2017) is well known for his contributions to the triphyletic theory of angiosperm origin and evolution. He was the Environment Resources Research Centre’s founding director. He was also regarded as the “Father of Indian Palynology.”

Pollen in Forensic Science

The study of pollen and other palynomorphs for evidence at a crime scene is known as forensic palynology.

Forensic Palynology

Over 50 years ago, Forensic Palynology became a tool for law enforcement. The use of pollen and spores in forensic palynology is used to resolve legal disputes, whether they are civil or criminal.

Palynological samples can be found in a variety of places, including people—on their skin, in their hair, or even in their nasal passages—vehicle tires, automobile air filters, on items, and even in mud. Pollen can be easily picked up and moved because of the ways that some plants disperse. It is simple for someone to unintentionally bring pollen from a crime scene onto their clothing or shoes, whether it be in the form of mud from stepping in it or from physically brushing against a plant in the vicinity.

Case Solved With The Help Of Pollens

During an outing down the Danube river, a man vanished. His murder was allegedly committed by another individual who had a reason to kill him; however, there was nobody and insufficient proof to support a conviction.

During the course of the investigation, a pair of muddy boots belonging to the defendant was found, and palynologist Wilhelm Klaus (University of Vienna, Austria) was contacted to examine the mud. He discovered pollen from living spruce, willow, and alder trees as well as fossil hickory pollen grains that were 20 million years old and had eroded from exposed Miocene sediment.

Only one small site close to Vienna met all of these requirements. As soon as the defendant was made aware of this information, he confessed to the killing and helped the police locate the victim’s body in the precise spot identified by Klaus’ study.

References

  • Mildenhall DC, Wiltshire PE, Bryant VM. Forensic palynology: why do it and how it works. Forensic Sci Int. 2006 Nov 22;163(3):163-72. doi: 10.1016/j.forsciint.2006.07.012. Epub 2006 Aug 21. PMID: 16920303.
  • Bryant VM, Jones GD. Forensic palynology: current status of a rarely used technique in the United States of America. Forensic Sci Int. 2006 Nov 22;163(3):183-97. doi: 10.1016/j.forsciint.2005.11.021. Epub 2006 Feb 28. PMID: 16504436.
  • Forensic Palynology. https://aboutforensics.co.uk/forensic-palynology/
  • Case Studies (Forensic Palynology). https://forensicfield.blog/case-studies-forensic-palynology/
  • Forensic Palynology. https://forensicfield.blog/forensic-palynology/
  • Mildenhall, D. C. Civil and criminal investigations. The use of spores and pollen. SIAK Journal. 4 (2008), pp. 35-52.
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