Field of Science

Parent Child Relationships continued...

The calyptra is a cap of maternal gametophyte tissue that covers the apex of the offspring sporophyte during development. My research shows that in the calyptra has a waxy cuticle that develops early and prevents water loss from the underlying sporophyte tissues. I think about this as the maternal gametophyte investing in these protective layers to keep the sporophyte safe from the harsh conditions of drying out as it grows taller and taller. 

This figure illustrates the maternal gametophyte calyptra
and its location across the stages of sporophyte development. 

An additional interpretation is presented by Haig. He views the waxy layers on the calyptra as slowing down or preventing the sporophyte from pulling up more water and potentially nutrients from the maternal plant.
 Haig, D. (2012). Filial mistletoes: the functional morphology of moss sporophytes Annals of Botany, 111 (3), 337-345 DOI: 10.1093/aob/mcs295

These differing interpretations of the same phenomenon are not mutually exclusive. One is not right and the other is wrong. As Haig mentions, both maternal protection and restraint are likely to be occurring at the same time. This relationship between mothers and their offspring is a phenomenon that is seen across the plant and animal kingdoms.

Parent Child Relationships

Relationships between parents and children are complicated. This is not only true for people and animals, but it is also true for plants. In this research paper Dr. David Haig explores the relationship between mothers and their offspring in mosses.
 Haig, D. (2012). Filial mistletoes: the functional morphology of moss sporophytes Annals of Botany, 111 (3), 337-345 DOI: 10.1093/aob/mcs295

This is a figure that I am working on for 
a paper that I am writing. It is still a work
in progress. If you have any comments or
suggestions for improvement feel free to
leave them at the end of the post.
In mosses the maternal gametophyte plant and the offspring sporophyte have a lifelong relationship. The offspring remain attached to and nutritionally dependent on the maternal plant throughout its lifespan, so nutrition is a major component of their relationship. These shared resources cause a conflict. The maternal plant needs to provide enough nutrients and water to the developing offspring for it to grow and mature, however, if the offspring takes too much the maternal plant may die. The offspring, on the other hand, is out to maximize its growth, despite any negative effects to the maternal plant. Haig goes into a more detailed discussion of the genetics behind this conflict, but what particularly interests me are his interpretations of moss structures and their functions in light of this conflict.

Stomata are cells with an opening between them. These pores enable gas to enter the leaves for photosynthesis in many plants. Additionally water escapes from the plant through these pores, drawing up water from the roots to the leaves. Haig's interpretation for mosses is that the stomata in the capsule are helping the sporophyte offspring to pull water and nutrients from the maternal gametophyte at higher rates. Thus increasing the resources that it is able to acquire. Often the photosynthesis explantation for moss stomata function is invoked, but I think that this is a really good alternative hypothesis for the stomata on moss sporophytes. As Haig so aptly said, "Sporophytes suck."

He also interprets the moss calyptra in light of this struggle between offspring and maternal plant. I am running a little late for game night, so the rest of this discussion is to be continued... 

Everyone wants to be called a Moss

There are plants that we call mosses that are not really mosses. Spanish moss (in the pineapple family), clubmosses (a fern friend), and carrageen moss (a red alga that is used in foods as a thickening agent)I like to call them mossy misnomers. Their common names include the term moss, but really they are not bryophytes nor do they look much like them. However, this stick insect is worthy of his mossy moniker. It is camouflaged to look like a moss and is doing an amazing job!

Trychopeplus laciniatus - Moss mimic stick insect
Photo by dandoucette on Project Noah

Crawling along on a moss covered tree the frills blend in with the surrounding moss making it hard for predators to spot this stick insect. Check out some of the great photos posted on Project Noah for this insect and many others. Thanks to my labmate Ciera Martinez for sending me this photo!     

Trychopeplus laciniatus on a moss-covered tree
Photo by dandoucette on Project Noah

The Zombie Mosses Rise from Beneath a Glacier

Mosses that were buried beneath a glacier for the last 400 years were able to resume growth. Fortunately these resurrected mosses will not be out to eat us. These findings were reported last week in the journal The Proceedings of the National Academy of Sciences by a Canadian research group led by Dr. Catherine La Farge. (As a side note we are academically related, she and my PhD advisor Dr. Bernard Goffinet were both graduate students of Dr. Dale Vitt. Does that make her my academic Aunt?)

ResearchBlogging.orgLa Farge, C., Williams, K., & England, J. (2013). Regeneration of Little Ice Age bryophytes emerging from a polar glacier with implications of totipotency in extreme environments Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1304199110

This is an amazing story of the ability of mosses to survive freezing in extreme environments. It is well-known that the leafy gametophytes and even the sporophytes of some mosses can survive the winter beneath the snow pack. These findings push our thinking about how long mosses can survive frozen far beyond what they have been shown to previously tolerate. That means that cryopreservation of mosses for 100s of years is not a farfetched idea for some species!

Figure 5b from La Farge et al 2013
Showing a region of new moss growth growing
from plants frozen since the last Little Ice Age (LIA). 

The authors bring up a number of interesting aspects to the research. Particularly I think that it really changes how I think about the colonization of plants in exposed areas post-glaciation. Not all of the plants may need to arrive from afar or recolonize from glacial refugia. Some of the bryophytes may just regrow from frozen but not dead plants.   

Figure 6c from La Farge et al 2013
Showing a petri dish full of mosses regenerated
from frozen plants.

If you are interested in reading more about the findings and hearing an interview with Dr. La Farge check out the following pieces. (There are many more online. These are just a few of the ones that I read and liked.)

Audio Reports

30 Second Science - A very short piece summarizing the major findings. 

NPR Talk of the Nation Science Friday - An approximately 12 min long interview with the lead author.

Written Articles

The Edmonton Journal - 400-year-old frozen moss brought back to life in scientist’s lab  - Biologists Revive 400-Year-Old Plants

BBC - Centuries-old frozen plants revived

Discovery News - Zombie Plants Return from the Dead

CBC - Includes an interesting thought about sending bryophytes to Mars.

June 2013 Desktop Calendar

I spent the past week visiting my family in Cincinnati, Ohio. We went for a ride on an old railroad bed that was converted into a bike path. This Fissidens was growing on a muddy bank at the edge of the woods. It was a nice day for a ride a little muggy, but pleasant with the bike-generated breeze. Now back to the dry heat of central California and my mosses in the laboratory.

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.