The Color of Light

Sunshine, to our human eyes the light appears white, but buried within are all the colors of the rainbow. In order for you or I to detect the colors that compose white light we need help. Shining light through a prism is one way I know to separate light into its many colorful components. Plants, on the other hand, need no such help. They have proteins called photoreceptors that enable them to detect different wavelengths of light. There are several different types of photoreceptors. Phototropins sense blue light, phytochromes sense red light, and neochrome is a chimeric protein that has the ability to sense both blue and red light. 

Light, especially the blue and red portions, are the main types plants use to run their photosynthesis machinery. When taller plants shade out shorter plants they alter both the quantity and quality of the light that reaches the plants below. Thus it is important that plants can detect the light quality in order to respond appropriately, by either growing away from shady spots or altering how they develop. 

A few ferns hanging out with their mossy pals.

A recent study was published that literally sheds some light on the evolution of these light sensing photoreceptors. Neochromes, the light sensing proteins with dual abilities, are present in only two groups of plants, the green algae and the ferns. Previously, scientists thought that these two groups independently evolved neochromes. But this new research proposes a different explanation. They found that the hornworts, a small group of bryophytes, also have neochromes and their proteins are closely related to those in ferns. They are so similar in fact that they were most likely transferred from hornworts to ferns. 

Horizontal gene transfer is a pretty wild thing that can happen in biology. One organism, potentially distantly related to another, can transfer some of its genetic code to another organism. If it is helpful the organism will keep the new piece of DNA, use it, and pass it on to its offspring. Scientists think that neochromes were very useful for ferns. Growing in the shadows of taller flowering plants, neochromes enabled ferns to take full advantage of low light conditions, thrive, and diversify. I think the ferns should send a thank you note to the hornworts for that super useful gift. The transfer of neochromes from one to the other happened over 150 million years ago, but you know what they say, better late than never.

Fay-Wei Li, Juan Carlos Villarreal, Steven Kelly, Carl J. Rothfels, Michael Melkonian, Eftychios Frangedakis, Markus Ruhsam, Erin M. Sigel, Joshua P. Der, Jarmila Pittermann, Dylan O. Burge, Lisa Pokorny, Anders Larsson, Tao Chen, Stina Weststrand, Philip Thomas, Eric Carpenter, Yong Zhang, Zhijian Tian, Li Chen, Zhixiang Yan, Ying Zhu, Xiao Sun, Jun Wang, Dennis W. Stevenson, Barbara J. Crandall-Stotler, A. Jonathan Shaw, Michael K. Deyholos, Douglas E. Soltis, Sean W. Graham, Michael D. Windham, Jane A. Langdale, Gane Ka-Shu Wong, Sarah Mathews, and Kathleen M. Pryer. Horizontal transfer of an adaptive chimeric photoreceptor from bryophytes to ferns. PNAS, published ahead of print April 14, 2014, doi:10.1073/pnas.1319929111

Additional coverage of this research can be found at these links: National Geographic, ScienceDaily, and The Economist. 

For more on plant colors, check out Johnna's April edition of the Berry Go Round plant carnival. My favorite is the post about the iridescent fruits of Pollia condensate. Pretty cool that they are the shiniest living things on Earth!

Do you have Pteridomania?

On the title page of her book Fern Fever: The Story of Pteridomania Sarah Whittingham informs us of the following definitions.

"Pteris Greek word for a fern, derived from pteron, meaning feather or wing. Pteridophytes The ferns and fern allies. Pteridologist One who studies ferns scientifically. Pteridomania Fern madness. Pteridomaniac One who suffers fern madness."

I just started exploring this book written about the Victorian obsession with ferns. It is a large coffee-table sized book with a myriad of color images and photos of all things fern. The introduction covers how the fern craze began in the 1850's with collectors traveling the world and sending ferns back to England for cultivation. With the invention of the Wardian case, a small terrarium, ferns were brought into people's homes. At the same time many authors were publishing books about growing ferns and the types of ferns native to Britain. Naturalist and gardeners alike could not get enough of them. Ferns even made it into fashion as a design embellishment on dresses. 

I think that it is going to be a fun and educational read. I would recommend it for anyone who is already obsessed with ferns or would like to join in the craze. It will also be appealing to the history-minded and lovers of the Victorian era.   

At this time, science was the realm of mostly learned, wealthy white men. Women with botanical interests, also white and wealthy, collected, drew, and dried plant specimens under the purview of a gentle hobby. They knew little about how ferns reproduced. One fantastical idea was that they flowered only once per year and the spores could only be collected at night. Around the same time Wilhelm Hofmeister was just publishing his findings on the alternation of generations and plant life cycles. Interesting to think how far science has come both in our knowledge about plants and increased inclusiveness of people from diverse backgrounds. 

I leave you with a poem that Sarah Whittingham includes in her book on page 40. I especially like it because it contains a shout-out to my favorite ferny friends, the mosses.  

Auld Botany Been was wont to jog

Thro' rotten slough and quagmire bog 

O'er brimful dykes and marshes dank, 

Where Jack o' Lanterns play and prank,   

To seek a cryptogameous store 

Of mosses and carex and fungus hoare, 

Of ferns and brakes and such-like sights

 As tempt out scientific weights

On winter's day; but most his joy

Was finding what's called Osman's Roy.

- Plues A Summer Study of Ferns  

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

Another Moss Misnomer

I am always on the lookout for plants called mosses that are actually not. I visited the Missouri Botanical Garden with some friends while in St. Louis a few weeks back for the Botany 2011 conference.  There I spotted this plant labeled Moss Fern. It is Selaginella pallescens, which is a lycopod or more traditionally called a fern ally. It is distantly related to moss as they are both green plants, but is definitely not a true moss. It has both vasculature (internal plumbing of xylem and phloem) as well as true roots to anchor it into the soil and function in water uptake.

There is a lot of plant life going on in this photo. The Selaginella is located behind the sign-post and also directly to the left. A few other species made it into the shot including a palm in the upper left and some mosses in the lower left.

There were quite a few other spots around the garden where mosses were growing, however, none of them were labeled. It is a bit of a bummer that the mosses are so blatantly ignored at a botanical garden. Here are a few shots from mosses inside the Climatron.

 

 

In general the garden didn't seem to add any fake animals to add to the tropical ambiance, thus this frog below looked a little out of place.

Some additional photos of the garden plants and me constantly looking for mosses can be seen over at my friend Em's blog. 

My Bryology Bookshelf - V

Another book that I picked up recently was a great book of fabulous images from Bill and Nancy Malcolm, entitled The Forest Carpet. This book is from the authors of the spectacular bryophyte glossary. They cover all three lineages of bryophytes (liverworts, mosses and hornworts), one lineage of ferns, a couple of fern allies (aka. fern friends), and lichens. The images are large, filling the pages of this coffee-table sized book. Each image comes with an informative caption, identifying the specific species pictured and notes the magnification. There are photos of the plants growing in their particular habitat, closeups of the exterior of the plants, and some sections showing the interior arrangements of the cells.

The goal of this book is to make people aware of the smaller organisms that make up the green background that covers the forest floor like a carpet in New Zealand, hence the title. I think that this book does a great job of immersing you into this miniature world!

Flora of Japan Online

I discovered today that there is an online version of the Flora of Japan. Unfortunately it does not include any bryophytes, so no mosses, hornworts, or liverworts. The website allows you search for your favorite vascular plants in Japan by family, genus, or specific epithet. Some of the interesting features are that is gives you the common name of the plant in Japanese, both in romanji (roman letters that allow you to sound out the word) and in katakana (japanese characters used for spelling out typically foreign words). It also lists the other things you might expect from a flora: a brief description of the plant and habitat, the distribution in Japan and other countries, as well as the reference to the initial description of the species.

I looked up the listing for Isoetes, the fern relatives (Lycophytes) that I studied when I was an undergraduate student. They have four species in Japan. One of them is even named in honor of Japan, Isoetes japonica, which would make the common name in English the japanese quillwort (quill - referring to the fact that the leaves are hollow and slender like the quill of a feather and wort - an Old English word for plant). Its common name in Japanese is Mizu-nira, which translates to water-scallion. Both of these common names quillwort and water-scallion are really great descriptions for Isoetes.

If you have never seen an Isoetes, I have included a couple of photos that I had saved on my computer. This is Isoetes riparia (shore quillwort) and I found it growing around the edge of the Mansfield Hollow Dam, which is just down the road from the University of Connecticut. When the water level in the dam is high this plant would be submerged in up to six inches of water. This is fine by the quillwort. It doesn't mind being wet. Isoetes are typically aquatic or shore-edge plants and are found worldwide.



I can hardly believe that there was a time long ago in a state far away when I studied ferns and did not have any particular interest in mosses. (Well ok, it was only six years ago in Ohio.) Though they are not mosses, Isoetes are really great plants and were super fun to study!

Questing for Fern Gametophytes (Part 1)

We spent an afternoon digging through moss mats looking for fern gametophytes. The main body that you would typically call a fern (the large, dissected, frond portion) is a sporophyte. Equivalent to this portion of the moss. Ferns also have gametophytes, however they are not nearly as large as the leafy green moss gametophytes. Fern gametophytes are typically less than a centimeter in size and one cell layer thick. We were particularly interested in finding gametophytes of epiphytic ferns. An epiphyte is a plant that lives on another plant. The plant that it lives on is called a phorophyte (phoro- meaning carrying or bearing). The epiphyte may are may not be parasitic on the phorophyte, but usually when people are talking about epiphytes in general they are not. The gametophytes of the epiphytic ferns are typically ribbon shaped and nestled within the fern mats that grow on tropical trees.

We collected moss mats off of trees and then dug through them in the lab in search of fern gametophytes. Here are some photos of the process and what I found with some of the photos below the fold.

Above is a piece of the moss mat that I was digging through. You can see my finger for scale.

This is one of the fern gametophytes that we found in the moss mat. I personally found one, but did not get a picture of it before passing it off to share with others. This is a ribbon-shaped gametophyte that is from a fern in the Hymenophyllaceae (filmy fern family).

While searching through the moss mat I came across this tiny snail shell. It is only a millimeter long, hence the fuzzy photo. It was so tiny and very cute.

The moral of the story is that there are tons of plants and animals besides moss growing in a moss mat. They are their own mini ecosystem. This idea is not limited to moss mats of the tropics. I have explored moss mats in Connecticut and found many interesting creatures.