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01/28/2010
Non-Plant Partnerships
I'm back! Been busy with my care giving duties - shopping, chauffeuring, laundering and cooking. Regarding the latter, I'm sure my wife would not classify me as a gourmet cook. I do feel that one thing I do well is to sauté mushrooms for such things as mixing with scrambled eggs or simply fortifying Campbell's mushroom soup. I just sautéed some of the fungi a couple days ago. I have always considered the mushroom to be a vegetable and a plant. But now I find I've been mistaken all these years. Am I alone in being thus misinformed?
Trying to justify my ignorance, I looked up "Mushroom" in my 1962 edition of my World Book Encyclopedia. Longtime readers will recognize that I've frequently referred to this source for all sorts of information, often finding the view more than four decades ago to be rather different than it is today. So, let me quote: "MUSHROOM. Mushrooms, or toadstools, which often grow from the ground as small umbrellas, are among the best known of the plants called fungi (italics mine)." The article goes on to describe how the bulk of the mushroom lies below the surface in the mycelium, a web of fine threads that in some fungi are packed together as tightly as in felt. The mushroom we see is a stalk that sprouts up with the umbrella, the sporophore, the part that bears the spores from which more mushroom plants are born. I feel somewhat relieved. At least in 1962, the mushroom apparently was a plant.
Many years ago, on one of our trips to a place whose location neither my wife nor I can remember, we both recall being impressed with some very colorful rocks along the road. On getting out to look more closely, we found that the colors of the rocks were due to a covering of plants known as lichens. Well, catching up on my reading recently, I found in the November 2009 issue of Discover magazine an article by Gordon Grice titled "Seeing the Forest for the Lichens". It was in this article that I discovered (a) lichens aren't plants, (b) fungi, and hence mushrooms, aren't plants, (c) lichens are actually a combination of fungi and algae unless (d) the algae are what were known as blue-green algae, now reclassified as cyanobacteria.
I am reasonably sure that in my youth we were taught that there were two "kingdoms" of life - Plants and Animals. Now I find the classification of life forms to be much more complex. Indeed, on browsing the Internet on such sites as those of Wikipedia, UC Berkeley, Utah State University, microscopy-uk.org (?) and the University of the West Indies, I find that the number of kingdoms espoused by various workers range from two to perhaps seven or eight or even more? There is still an Animal Kingdom, defined as the kingdom containing multi-celled organisms born through the uniting of a sperm with an egg. David Goldstein, on the microscopy-uk site, notes that you might want to question this definition. There's a lizard that reproduces by parthenogenesis, i.e., no male or sperm is required. Yet who would question that this particular lizard is not an animal just as is any other lizard? One of the many exceptions that proves the rule?
The Kingdom Prokarya or Bacteria, comprises "prokaryotes", in which the cells do not have nuclei bound by a membrane. All the other kingdoms are "eukaryotes" - the cells do have nuclei bound by membranes. The blue green algae were reclassified as cyanobacteria because they were found to be prokaryotes. Why aren't my mushrooms plants? That's because the Kingdom Plantae, plants, generally have rigid walls of cellulose, in addition to being formed sexually from male and female cells (with some exceptions as with that lizard). Most plants also engage in photosynthesis and don't move around, but stay put in one place. In the Kingdom Fungi, the fungi cell walls aren't cellulose but chitin, a substance found in the animal kingdom. So, some claim that fungi are more closely related to us animals than to plants! Fungi range from my mushrooms to Athlete's foot fungi, those pesky little critters portrayed so erroneously in TV commercials.
What about the algae other than the reclassified blue green algae? We find them in the Kingdom Protoctista. This kingdom serves as a sort of free for all in which those not fitting into the other categories find a home. As I get it, they are all eukaryotes and the kingdom includes algae and protozoa, as well as slime molds and even giant kelps growing to 30 feet in size. As I mentioned above, some feel that there should just be two kingdoms -eukaryotes and prokaryotes, while others feel some of the five kingdoms should be split even further.
But enough of trying to classify life. Let's get back to the lichen. As we said, lichen is not a plant, but a mutually beneficial (symbiotic) combination of a fungus and an alga or a cyanobacterium. (Sometimes, more than two partners may be involved.) The dominant player in this partnership is always the fungus, for which the various types of lichen are named. What do the algae and the fungi do for each other? The fungi provide protection for the algae by enclosing them within the structure of the lichen. This structure shields the algae from strong sunlight and also retards any drying out of the algae.
The algae or cyanobacteria contain chlorophyll, which allows photosynthesis, the process involving sunlight, carbon dioxide and water to make food to nourish both the algae and the fungi. Cyanobacteria also can help themselves to nitrogen in the atmosphere to make amino acids, providing a more varied diet than do the algae. Lichens have a remarkable ability to take up water from dew, fog or from humid air. They dry out very slowly and lichens can be found in deserts and in polar regions, thanks to their ability to absorb and maintain water. It also explains their ability to grow on bare rocks, not needing the rocks to provide anything in the way of nourishment.
Of what use are lichens for us? The Scandinavian Lapp people stockpile so-called reindeer lichen as food for what else - their reindeer. At the other extreme, sheep in Libyan deserts eat lichen growing on rocks. Some compounds produced by lichens are used in various medications. In the past, lichens were used to make dyes but synthetic dyes are more colorful and longer lasting. However, there is still one commercial dye derived from lichen that is dear to the hearts of chemists. Is there any chemist or chemistry student who has not somewhere along the line used a piece of litmus paper containing a lichen dye to test whether a solution is acidic (red) or alkaline (blue)?
Lichens can live a long time, hundreds of years, possibly even longer. As noted, lichens can live on rocks. Lichens do a couple of things that can turn rocks into soil. By growing into tiny spaces they can cause cracks in the rocks and they also release chemicals acidic in nature that dissolve the surface of the rock; both processes free up mineral grains in the rocks. These grains help to create new soil, which consists of such mineral grains and organic matter from decayed plants.
Could this soil-making property some day help pave the way for humans living on Mars? This unlikely "Big Idea" is posed in a feature on "Terraforming" in the February 2010 issue of National Geographic. The big idea is that Mars could be made Earth-like over a period of millennia if it only were heated up in some manner. How? Introduce a powerful greenhouse gas such as the perfluorocarbons we have banned here in part because of their greenhouse effectiveness. Once Mars has warmed up sufficiently, frozen carbon dioxide would be released, adding to the warming effect. Eventually, ice would melt and water would flow. The atmosphere would become humid to some extent. Now add bacteria and lichen to grow on the rocks and form soil. Wait a millennia or so and seed the planet with redwoods and other plants. An atmosphere containing at least some oxygen would result and we can set up camp, at least on a research basis. We can't wait too long, however, as eventually the atmosphere will return to what is was before the Big Idea project took place and Mars will again freeze over.
Hey, this is indeed a BIG idea! While I can't imagine it being attempted any time in the foreseeable future, who knows? As our sun begins to die and expands to gobble up Earth there may be a need to go out to Mars for a while and buy some time before our whole solar system gets disrupted by the Sun blowing up and forming a neutron star. Perhaps a few intrepid souls will be dispatched in another Big Idea spaceship capable of providing food and sustenance for a crew of individuals and their progeny headed for an Earth-like planet discovered back in the 21st century by the Kepler mission launched in 2009. (Kepler has already reported discovery of five planets, though not yet any capable of supporting life.)
Meanwhile, let's enjoy the time we have here on our own planet. And keep eye on those lichens. Highly sensitive to air and other types of pollution, they can serve as one of the many canaries warning us about the increasingly sad state of our environment. One can argue that the biggest threat to the Earth's environment is our human tendency to reproduce ourselves at much too great a rate. On a foldout page immediately following the Big Idea feature, National Geographic has a picture that graphically illustrates this tendency. The photo is of 88-year-old Joe Jessup, his five wives, 46 children and 239 grandchildren! Jessup is an elder of the Fundamentalist Church of Jesus Christ of Latter Day Saints (FLDS), a sect that was formed after the Mormon Church banned polygamy. It's a frightening article. On the other hand, if we ever want to go to Mars and populate that planet, sending FLDS members might be the ideal solution!
Well, so much for this, my first irregularly posted column. I'll try to post another one by the end of February.
Allen F. Bortrum
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