To study pollen germination on a slide first we need to understand what the meaning of pollination is and how it germinates. It is an essential part of a flowering plant's life cycle. Pollination is a process where pollen grains are transferred from the anthers to the stigma of the same or different flowers unlike the study of pollen germination on slide. This process is interceded by biotic and abiotic means. In biotic means, the pollination is carried out by a mediator such as animals, birds, and insects. Abiotic means the pollen is transferred through a non-living substance such as wind or water and not an organism.
When we study pollen germination on a slide the observation differs.
How Pollen Germination Works?
Just like we study pollen germination on a slide, the process is carried out through stigma in plants. In flowering plants, it is the pistil (a hollow organ in ovules of a plant) where pollen grains are being deposited. The actual process of pollen germination starts on the stigma when water and nutrients are absorbed, and the pollen grains have a tiny pollen tube protruding from the ovary.
To understand this whole process a little better, let us carry out an experiment to study pollen germination on a slide
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Aim: To Study Pollen Germination On A Slide (Grass, China Rose, Portulaca, Etc.)
Apparatus (you need): A seasonal flower (preferably china rose or portulaca), Coverslips, Slide, Microscope, Chemical like 10g sucrose, 10 mg boric acid, 20 mg magnesium sulphate, 30 mg calcium nitrate, 100 ml Distilled water, Beaker, and a dropper.
In this experiment to study pollen germination on a slide, start the procedure by creating the nutrient solution. Pour all the above-given chemicals in 100 ml of distilled water into a clean beaker. A nutrient medium is formed.
Now, take the fresh mature flower and dust some pollen grains from the stamens onto the dry and clean slide.
Take a dropper and add a few drops of the nutrient medium on the slide over the pollen grains.
To get the right output and to study pollen germination on a slide correctly let it rest aside for 10-15 minutes.
Now, observe the slide under the microscope. Keep it low power. Review it every 30 minutes.
Record your observations in your record sheet and draw a well labelled diagram.
This way the study of pollen germination on slide is carried out.
When the pollen grains get submerged into the nutrient medium, it germinates. The germinated pollen grains are called as viable grains.
During the study of pollen germination on slide, the augmentation of the tube cell/vegetative tube is observed. This eventually turns into a pollen tube after emerging from the germ pores.
The cell nucleus turns into the pollen tube and gives rise to two male gametes also called sperm nuclei which are lenticular or spherical in outline.
The pollen grains that do not develop into a pollen tube did not germinate at all. These are called as non-viable pollen grains.
In this experiment to study pollen germination on a slide the germinated pollen grains are viable.
When you study pollen germination on a slide keep these things in mind:
Do not use dirty slides for dusting pollens, make sure it dry and clean.
Drop only a few drops of the nutrient median (2-3 drops).
The observation is carried out on a cavity slide that has a depression at the centre.
Use freshly plucked flowers only.
Make sure you don’t forget these points while carrying out the study of pollen germination on slide
During the study of pollen germination on slide, the formation of pollen grains is known as microsporogenesis. These structures may vary in size and be spherical, triangular, or oblong depending on the species.
Mature pollen consists of two layers called exine and intine. When you experiment to study pollen germination on a slide you will observe that the exine is thin and delicate in certain places which are known as germ pores. From these germ pores, the male gametes protrude out with intine (pollen tube) and other cells.
Some plants prevent Self-pollination using toxins: Some flowering plants reject pollen produced by the plant itself and prevent itself from self-fertilization. Once it identifies the pollen as “self” it naturally blocks the germination process. The same goes when you study pollen germination on a slide.
Plants use tricks to spread the pollen: Flowers use tricks to lure the pollinators and carry the pollen. Some plants are bright in the dark and appeal to nocturnal insects such as moth whereas some plants allure insects by spreading its smell.
1. Why Do Some Pollen Grains Fail to Germinate?
Even during the experiment to study pollen germination on a slide, you will observe that some pollen grains fail to germinate. Sometimes the nutrient mixture fails to do the job and in real life when pollen doesn't germinate, it’s because sometimes when the grain falls on the stigma it does not get the right conditions to carry out germination. To study pollen germination on a slide correctly remember, all pollen tubes don't have the same length and the newly developed ones have smaller tubes, unlike the old ones which are longer in size. The tube will not reach the stigma if not germinated.
2. Why Do We Use Sucrose as a Medium for Pollen Germination?
The natural process allows the pollen germination only on the compatible stigma. It is the stigma that stimulates the germination process by producing a sugary liquid. The study of pollen germination on a slide is the same because sucrose fulfils multiple criteria that are important to carry out the pollen germination such as a substrate for the pollen metabolism and required osmotic pressure. Therefore, to study pollen germination on a slide, you will notice sucrose produces the right tube growth in vitro for pollen germination. This is the precise reason why we use sucrose as a medium for pollen germination.