Pollen grain

Introduction

Pollen grains are the biological basis of plant reproduction. Grains produced by a mature flower participate in a process called pollination -a fusion between male and female flower parts.  Pollination is the process where there is a transfer of pollen from a male part of a plant to a female part of a plant which indirectly assists in the production of seeds. The study of pollen and spores is known as palynology.

 

Table of Contents

1. Introduction

2. Structure and characteristics of pollen

3. Uses of pollen (commercial and domestic)

 

Structure and characteristics of pollen

Ovum and ovules are female gametophytes whereas the pollen grains are the male gametophytes. Pollen is a substance that feels like grains when you touch an opened anthers. Colour may vary between yellow, dark yellow, white, red, purple, orange, etc. When you closely watch the sticky pollen under a microscope, you see a wide variation in their sizes, shapes, designs and other morphological features. Pollen measures approximately 25-50 micrometres of diameter with a spherical look. A typical pollen has a central nucleus that performs fertilization and the prominent two-layered outer walls. The outer layer is called exine which is made up of sporopollenin -a tough and resistant organic material.  Sporopollenin can resist harsh climatic conditions like very high heat from sun, corrosive effect of strong acids and alkali. It is not influenced by any enzymes to get degraded. Pollen grains are able to sustain their true structure and nature so long that they can be preserved as fossils, this is due to the strength given by sporopollenin. Intine is the inner wall of the pollen grain. Intine is structurally made up of cellulose and pectin. After the exine and intine, the fertilization zone begins with cytoplasm surrounded by a plasma membrane. In a mature pollen grain(Papaver dubium L), there are two cells namely the vegetative cell that has a rich supply of food and nutrients and a generative cell( see image below) that floats in the cytoplasm of the vegetative cell as shown in the picture below. About 60 % of cases, pollen grains are shed at this 2-celled stage (vegetative, generative) but the rest others undergo cell division mitotically to reach the 3-celled stage.  Pollen shedding requires a flower to be completely matured, the temperature of the environment to be generally hot, When the pollen has shed, they have a viability period (period of survival) until then the pollen is active and energetic to fertilize. Fortunately, the period of viability of pollen grains is very high even in the prevailing temperature and humidity. Viability varies between species, for example, in some cereals such as rice and wheat, pollen grains lose viability within 30 minutes of their release, but certain members like Rosaceae, Leguminosae, and Solanaceae, the viability stays for months.

 

Uses of pollen (commercial and domestic)

Pollen is sold in packed products, honey bee farmers use pollen to refill the nutritional requirement of honey bees. Since pollen grains are rich in nutrients, pollen tablets are used as supporting nutrition. In many experimental studies, pollen consumption has proved a boost in the performance of athletes and racehorse. NOTE: There are many allergic diseases which gets triggered when our body parts exposed to pollen hence, it is allergic in nature. People with skin allergy, asthma, bronchial inflammatory disorders are at high risk for pollen allergy.

 





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