Pollen germination

Those fascinating observations from pollen grain germination in the Brahma Kamalam drew me  irresistibly towards flowers of other plants. Recently I have been watching educational videos as now I am planning to create videos for school students using Foldscope images. In the biology videos for Classes 11 & 12 I noticed that Vinca rosea (Periwinkle) is commonly used to show pollen germination.

I decided to try that with the medium that we had earlier used to observe the Brahma Kamalam’s pollen. I took a drop of solution on a glass slide and dusted the pollen onto it.

Within just a few minutes the pollen started germinating.

The foldscope was attached to my iPad and I quickly pressed the time lapse option. I stopped after 20 minutes and replayed the video. I kind of lost the full field of view but you can see towards the end that two of the pollen tubes suddenly burst and the plasma pours out.

I then scanned the slide and found many pollen grains interlocked with pollen tubes. It looks like cent percent germination.

Next I took pollen from a  just-bloomed flower, attached a Foldscope to my iPad and left it for an hour on time-lapse. Here I saw various events: plasmolysed pollen, burst out pollen and germinating pollen. Notice that the fast-growing pollen tube near the top is connected to the most hectic activity inside the pollen grain!

Next I turned to the older flowers and recorded for one hour. Hurray! Almost all the pollen grains germinated and the plasma movement was clear too.

It is my first perfect time-lapse video. Watch and enjoy!


 I continued my observations with Mirabilis Jalapa flower (also known as the four o’clock flower).

This is the largest pollen grain I have observed. Again I put the pollen into the medium. Before starting the time lapse I saw that some pollen grains were open.

This time too, I recorded an hour’s footage as a time-lapse.

No change, not even the slightest movement in the protoplasm. Is this medium not working on this plant pollen? Or is the pollen grain not viable?

The next victim in my hand was Zephyranthes candida (rain lily). Usually these flowers open at night and release pollen at dawn. I collected this flower at noon and noticed its anthers were intact.

I tore the anther and dusted pollen into the medium. The pollen grains were oblong in shape. I took a time-lapse video for an hour. Here we can see slight movement in the protoplasm but no indication of germination. Is this because of late anthesis? I should have waited to collect the pollen at their natural time of release.

My next victim was yet another sacred plant, Ocimum tenuiflorum (Krishna tulsi) or holy basil. It has small purple flowers with yellow anthers, and the smallest pollen grains I have ever observed. This image shows the hexacolpate pollen.

Again I tried a time-lapse video for one hour. It shows the tiny grains of pollen sitting around a large anther. I noticed minute movement in the pollen grains but not much change.

From all these observations I came to the conclusion that this medium had some effect on Epiphyllum oxypetalum (not clear if it was germination) and Vinca rosea (definitely germination). In pollen germination concentration of medium and temperature are important factors. Maybe the change in proportions of calcium, boron, sucrose and magnesium influences the germination of pollen.

There are so many possibilities for studying the germination of pollen of different plants. Slowly this Foldscope is dragging me towards research into something that is unknown to me. 

Cheers,
Ashalatha

6 Comments Add yours

  1. Manu Prakash says:

    Dear Ashalatha,

    What a fantastic series of observations; reminding again so much is hidden right under our eyes!

    Just an incredible post. So many questions and ideas pop up once anyone sees this.

    Also; could you please list your germination solution and exact ingredients – it would be amazing for everyone to replicate these with a large number of pollen!

    Cheers
    Manu

  2. edurafi says:

    Such an amazing post! Timelaps videos are just wow! Can you list the chemicals you used for germination, I want to try it.

    1. @manu, @edurafi – In the last post Chandrika described how she and others in our outreach group collaborated to prepare the ‘germinator solution’. To recap: in 100 ml distilled water dissolve 20 mg potassium nitrate + 30 mg magnesium sulphate + 10 mg boric acid + 10 g sucrose.

      Thanks to your questions, I re-visited the ingredients of the Brewbaker and Kwack medium that I had cited in this post and realised that those proportions are different from ours, and also they use calcium nitrate in addition to potassium nitrate. I have edited this post to remove the incorrect reference. Sorry, that was careless of me!

      Interestingly, Brewbacker and Kwack say (in a 1963 paper) that calcium ions play an essential role in pollen germination and pollen tube growth. So we may be missing an important ingredient in our solution.

      Great to be part of this learning community!

      Cheers
      Ashalatha

  3. Cristina says:

    Absolutely amazing! I can observe one pollen tube per pollen grain. I was wondering if there could be more than one as many exhibit three or six apertures (I suppose it has to do with gamete arrangement after meiosis: four gametes, four pollen grains). Indeed this would lead to a minor genetic variation but somewhere it may have ocurred, I guess.

    And what aperture will be used? The one in contact with the stigma? What about a pollen grain that lands or is deposited with its apertures equally distanced from such surface?

    Also, there are pollen grains with no apertures. What happens in order to burst and consequent pollen tube growth?

    Again, awesome post!

    1. Thank you, @cristina for your appreciation and for raising so many interesting questions. It’s a nice observation that most of the pollen grains appear to have (I think) three apertures. As far as I could tell, only one tube was growing from each grain. What made one tube grow rather than another, especially when there was no stigma to stimulate growth? Could it be some local variations of ions in the medium?

      In the last post I did observe some polysiphonous growth. I am not sure if it was from natural apertures or just anomalous rupturing due to properties of the medium.

      Much to learn. Thanks again!

      Cheers
      Ashalatha

  4. Ronak Hati says:

    I have some questions looking at the gorgeous pollen tubes 😍

    Do germinating pollens compete with each other to be able to reach the ovary?

    I wonder what role could pollen grain number per stigma play in the time taken for pollen tube growth and maximum length of the tube before they burst. The pollen tubes observed through the foldscope look much shorter than the length of the style of the gynoecium (they burst before reaching a significant length). Maybe they burst because the tube is growing in a liquid medium rather than through the style.

    Also, could there be a link between pollen grain size and the length of the style of the flower? This may be an interesting project to do with the foldscope.

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