Investigatory Project on Pollen Grains

 

STUDY OF POLLEN STRUCTURE AND CALCULATION OF POLLEN VIABILITY

Introduction

The pollen grains or microspores are the male reproductive bodies of phanerogams. They are produced in sac like structure called microsporangiurn. The pollen grains are usually spherical in shape, but the shape Varies from species to species. A pollen grain has two wall layers. The outerthick exine, is made up of highly resistant sporopollenin and inner thin intine, is made up of pecto-cellulose. The exine provides a characteristic sculpturing over the surface of pollen grain. It helps in identification of the species to which a pollen grain belongs. The study of external morphological features of pollen grain is called palynology.

The insect pollinated pollen grains have a yellowish sticky and oily covering over the exine called pollenkit. In the exine here and there small thin areas are present. These are called germpores. The pollen grains are usually liberated at two celled stage - a large vegetative cell or rube cell and a small generative cell. The pollen viability refers to the ability of a pollen grain to germinate and produce male gametes.

Materials and Methods

The following materials are required for this project - flowers of different plant species, cavity slides, plain slides, cover slips, microscope, beakers, measuring cylinder, sucrose, boric acid, magnesium sulphate, potassium nitrate, reagent bottle etc.

Pollen structure

First of all carefully observe the structure of the pollen grain and draw its diagram. For this take a clean slide and put a drop of glycerine on it. Dust a few pollen grains from the anther of a flower in the glycerine drop. Place a cover slip and observe the slide under the microscope using low power and high power and draw diagrams. Similarly study the structures of pollen grains of different plant species.

 

Pollen viability

After studying the pollen structures study the pollen viability. For this, prepare a nutrient solution by dissolving 10g. Sucrose, 10g Boric acid, 10mg KNO₃, 10mg MgSO₄ in 100 ml of distilled water. Keep this solution in a reagent bottle. This solution acts as a nutrient for the developing pollen grains.

From this solution take a few drops and put on a clean cavity slide. Dust pollen grains from mature anther of the flowers over this solution. Observe the slide under dissecting or compound microscope after 5 minutes and then regularly after every minute. Similarly perform experiment with different types of flowers and record the germination of pollen grains of each species.

 

Observation and Result

The pollen grains of different plant species show different sculpturing on the exine. The distribution and pattern of germpores also vary in different types of flowers. The rate of germination and viability of pollen grains of different species also differ. Record the observations in the following table.

Viability of pollen grains of different flowers

No:	Name of flower	Time taken for germination of pollen grain	No: of viable pollen grains	No: of non viable pollen grains	Percent viability
1 2 3 4 5 6 7

Discussions and Conclusions

Some of the pollen grains placed in the nutrient solution, germinate and some do not germinate. This is because the viable pollen grains only germinate and non-viable pollen grains do not. The percentage of viability varies in different flowers.

Viva Questions and Answers

1. What are pollen grains?

Pollen grains are the male spores produced in anther.

2. What is palynology?

The study of external morphological features of pollen grain is called palynology.

3. What is exine composed of and what is its importance?

Exine is the outermost wall layer of pollen grain composed of a hard and resistant material called sporopollenin. It helps the pollen grains to withstand adverse environmental conditions.