Field of Science

Dr. Jekyll & Mr. Hyde: Alternation of Generations in Plants

Dr. Friedman uses the analogy of Dr. Jekyll & Mr. Hyde to describe how plants have two different generations in their life cycle in this Science, Perspectives article.

Friedman, W. (2013). One Genome, Two Ontogenies Science, 339 (6123), 1045-1046 DOI: 10.1126/science.1234992

All plants have two distinct life stages/generations. The gametophyte has one set of chromosomes per cell and the sporophyte has two sets per cell. In many plants, including the bryophytes, ferns, and seed plants these generations have wildly different forms, as distinct as the personalities of Dr. Jekyll & Mr. Hyde. The wild part is that the main genetic difference between the two generations is just dose. One has 1 set of chromosomes and the other has 2, but their sizes, shapes, and numbers of cells are amazingly different! Check out some examples below. (These pairs are not necessarily of the same species. I just wanted to pull together some examples for a visual.)

Moss Gametophyte 
Size: Shorter than your pinky fingernail.

Moss Sporophyte 
Size: As tall as your pinky finger.

Fern Gametophyte
Size: Fits on the end of your finger.
Fern Sporophyte
Size: Tips of the leaves at or below hip height.
I borrowed this photo from Emily's fern blog.

The evolution of this alternation of generations has long interested scientists. How is the difference between these two morphologies controlled? Well a piece of this puzzle has been recently figured out. Researchers report that they have discovered a gene, KNOX2, that suppresses gametophyte morphology. When this gene is turned off in a moss sporophyte the plant starts to grow but does not develop into a mature sporophyte, but instead grows into the shape of a leafy gametophyte plant. It is an elegant study and a great addition to our knowledge about the genetic control behind the transition between these two distinct generations! 

Sakakibara, K., Ando, S., Yip, H., Tamada, Y., Hiwatashi, Y., Murata, T., Deguchi, H., Hasebe, M., & Bowman, J. (2013). KNOX2 Genes Regulate the Haploid-to-Diploid Morphological Transition in Land Plants Science, 339 (6123), 1067-1070 DOI: 10.1126/science.1230082

March 2013 Desktop Calendar

Apologies for the delay in the March calendar. I have been busy working in the lab getting my moss cultures started! They are currently at the filamentous protonema stage and are growing nicely as you can see from the photo below.

I am not sure which species made it to the top of the pile for best photo. It is definitely a Funariaceae, but could be Entosthodon, Funaria, Physcomitrella, or Physcomitrium. It is impossible for me to tell which one at this stage of development (and I forgot to check the plate), but once they undergo reproduction their sporophyte capsules are strikingly different. They are still months away from that growth stage, so let the growing continue!

1 - Single click on the image to open it up in a new window. (If you use the image directly from the blog post you will lose a lot of resolution.)

2 - Right-click (or ctrl-click) on the image, and chose the option that says, "Set as Desktop Background" or "Use as Desktop Picture". The wording may vary.

3 - If the image does not fit your desktop neatly, you may have to adjust the image (Mac: System Preferences - Desktop and Screen Saver - Desktop; Windows: Control Panel - Display - Desktop) and choose "Fill screen" as the display mode of your background image.

Berry Go Round - February 2013

The newest edition of the plant carnival Berry Go Round has been posted at Foothills Fancies.  There are some fun plant posts in the line up that you should definitely check out. I especially like the animated gifs of bees pollinating!

For more about blog carnivals and my posts about the earlier editions of Berry Go Round, click here.