Karpechenko, Polyploidy, and Other Long Words

Greetings, everyone! It’s the second Saturday of the month already, and I am delighted to be here talking about one of my favorite science topics with you. As you may know, or may have guessed from reading my blog and noting the disproportionate amount of genetics posts, I am a genetics major, major DNA nerd, and plant biology minor. I’m going to bring all those things together in this post, so hold on to your hat and let’s have some fun!

As with many of my science posts, our topic today stems from a class I am taking (Evolutionary Genetics of Plants, in this case). My teacher told us a story, which I thought was cool, so I am now going to repeat it to you.

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The story was about this guy.

The guy in the picture above supplies the first of the long words in this post: his name, Georgii Dmitrievich Karpechenko. As you may have guessed, he was Russian. Specifically, he was a Russian botanist and plant cytologist (cell biologist) who did some interesting experiments with plant breeding. Let’s explore them.

Presumably, Karpechenko enjoyed both cabbages and radishes, or else he just wanted to contribute to improved agricultural productivity in his nation of limited farmland, or possibly both. Either way, he wanted to create a plant that produced a cabbage in the shoot and a radish in the root. The logical way to do this (his reasoning presumably went) was to cross a cabbage with a radish.

Here we have to back up a bit and get into some more long words. Cabbage and radish are different species, but not only that, they are in different genera (the first word of a scientific name); cabbage is Brassica oleracea and radish is Raphanus sativus. Usually, the definition of a species is “a population which is reproductively isolated (i.e. can’t breed) from others.” Of course, the only thing in science with no exceptions is that everything has an exception, and Karpechenko was indeed able to breed his cabbage and radish (for reasons we haven’t talked about in class yet) and produce a hybrid plant.

Well, unfortunately for Karpechenko, his hybrid didn’t look anything like either a cabbage or a radish. It was just a weed. Worse yet, it was a sterile weed; it produced seed pods, but no seeds. Fortunately for botany and genetics, though, Karpechenko didn’t give up on his experiments just yet. He kept observing his plants and noticed one day that a branch of one of them was producing seeds, even though the rest of this plant continued to be sterile. Furthermore, when he planted the seeds, they gave rise to fertile (if weedy) plants, and a new head-scratcher: how could this be?

Backing up again: The fertility of plants (or any organism, really) arises from a special cell division process called meiosis, which some may have learned about in high school biology. Most organisms are diploid, that is, they have two complete sets of chromosomes. For example, humans have 23 chromosomes in a set, and a total of 46 chromosomes in two sets. It works the same way for cabbage and radish; each has 9 chromosomes in a set, and 18 chromosomes total. This comes from reproductive biology; in any diploid organism, one of the sets of chromosomes comes from each parent. So in order to reproduce, plants (and animals, and fungi) have to produce haploid gametes, “sex cells” with only one set of chromosomes apiece. (In humans, we know them better as the sperm and the egg.) This is what meiosis is all about.

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A summary figure of meiosis. Note the homologous chromosomes separating into different cells; don’t worry about the different colors.

 

In order to reduce the chromosome set number, or “ploidy,” from diploid to haploid, chromosomes line up in matched (“homologous”) pairs and separate into two new cells (see the figure above). These cells then undergo further division to form gametes, the details of which we won’t worry about.

Now let’s think about Karpechenko’s sterile hybrid. This little weed had one set of chromosomes from cabbage and one set from radish, which enabled it to grow and function. However, when it came time for meiosis, it turned out that radish and cabbage chromosomes were different enough that they wouldn’t pair and divide into different cells, and no gametes were formed, which ultimately meant no seeds.

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Karpechenko’s experiments shown as seed pods. “Amphidiploid” is the same thing as tetraploid.

 

So what about that branch that became fertile? Well, it turns out that plants sometimes spontaneously undergo whole-genome duplications, in which, just as it sounds like, the entire genome of the plant is duplicated in the cell. (This happens routinely before cell division, but then it all divides into two cells. In whole-genome duplication, what happens is that the cell thinks it’s divided, but actually hasn’t, and now has four sets of chromosomes rather than two.) This happened in Karpechenko’s plant, in a branch precursor cell, and gave rise to a tetraploid branch, having four sets of chromosomes, two from radish and two from cabbage. Now, suddenly, all chromosomes had homologs to pair with in meiosis, and seeds could form.

Karpechenko had discovered polyploidy, the state of having more than two chromosome sets, which turns out to be a rather important phenomenon in plants. Besides generating greater genetic diversity, helpful to plant breeders, polyploidy results in more DNA, bigger nuclei, bigger cells, and eventually, bigger, more robust plants overall. It’s so useful that plant breeders sometimes induce polyploidy with chemicals to help in developing new varieties. Many important plants, such as wheat and canola, are polyploids.

What happened to Karpechenko himself? Well, in the early 20th century, the Soviet Union’s leadership was not big on genetics. In 1941, Karpechenko was arrested on a false charge and executed, but not before making a major contribution to botany and genetics.

What do you think? Have you heard of Karpechenko before? What about polyploidy? (Isn’t it cool?) Do you have any questions? Tell me in the comments!

Chlorophyll, Carotenoids, and Anthocyanins, Oh My (Why Leaves Fall in the Fall)

Well, it’s October, which means that here in New England, it must be leaf-peeper season. Drive up Interstate 93 anytime around now, and you’ll probably see hordes of license plates from more southerly states on cars packed in to see the leaves in the White Mountains. We residents refer to them fondly as “leaf-peepers” (and sometimes do some leaf-peeping ourselves).

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The White Mountains with fall colors.

 

So what does all this have to do with those three long words in the title of this post? Well, for my science post this week (which I normally do on a second Saturday, but I had a guest post  last week–check it out if you haven’t yet!), I thought it would be seasonally appropriate to talk about the biology behind leaf colors, the defining symbol of fall. And since I’m interested in plant biology, this is also right up my alley.

So during the spring and summer, leaves are green. This is because of Pigment #1 listed in the title: chlorophyll, the major photosynthetic pigment in plants. Chlorophyll is very important for exciting electrons and causing biochemical cascades and so forth, and all of that eventually leads to the plant producing its own glucose, which it can then use in respiration to essentially make energy for cellular mechanisms. So for most of the year, trees are green. Then why does it change in fall?

Well, in the fall, the weather starts getting colder, and the plant starts to go dormant in order to survive the winter. As the U.S. Forest Service explains, leaves are thin and contain a lot of water that could easily freeze in winter, so deciduous trees must get rid of them in order to survive each winter. And as nights get longer in the fall, the plant senses that it’s time to get rid of the chlorophyll, and Pigments #2 and #3, carotenoids and anthocyanins, show their colors, so to speak. Carotenoids, which are always present in leaves, cause yellow and orange colors. Anthocyanins, produced only in response to sugar buildup, cause reds and purples.

What affects leaf color? Well, you may have noticed it depends on the kind of tree. Oaks mainly have brown leaves (which, incidentally, don’t usually fall off until spring), beeches have lighter brown, and maples can be orange or red or other colors depending on the species.

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Maples in fall.

I found it interesting to learn that weather also affects the colors of leaves. Warm, sunny days cause buildups of sugars, and cool nights constrict the plant’s vessels, causing the sugars to stay in the leaves and the subsequent production of anthocyanins. Soil moisture can also affect leaf colors; if there’s a summer drought, for instance, color onset will be delayed a bit. The best colors occurs if there’s a warm, wet spring and good summer weather, according to the Forest Service.

One last question: what causes leaves to actually fall off? Starting early in the fall, xylem and phloem veins (veins that bring water and nutrients to leaves) start to close off, eventually leading the leaf to fall. The tree is left with only its winter-hardy tissue, giving it a better chance of surviving the winter. As an addendum, some trees actually have winter-hardy leaves that only fall due to old age. We know them as the evergreens: pines, spruces, hemlocks, and other trees with needle- or scale-like leaves. The waxy coatings on their leaves make them hardy enough to keep on photosynthesizing all winter long.

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Which is why people use evergreens as Christmas trees: they’re still green.

 Are your leaves turning colors yet? Have you ever thought about why they turn colors in the fall? Are you going to go “leaf-peeping” this fall? Tell me in the comments!

Class Project to Blog Post: A Word on Photosynthesis

Greetings! Once more, it is the second Saturday of the month, and I find myself scrambling to put together a post about science. Fortunately, I’m a genetics student two weeks into her third semester, and need not look too far for interesting topics.

Inspiration comes in various forms. Why shouldn’t it come in the forms of happy little houseplants?

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A jade plant, Crassula ovata.

I’ve kept jade plants for years. They’re a kind of succulent (a water-conserving plant with fleshy stems and leaves, something between a normal plant and a cactus) which, not surprisingly, grows well even when you forget to water it. Plus, every time a branch breaks off, if you stick it in a pot, you get a new plant. (I keep getting more of them that way.) They look cool, make great bonsai projects, and even flower once in a blue moon. And as this is a science post, not a gardening post, I bet you’ve already guessed that jade plants are also scientifically interesting.

All plants use photosynthesis to “fix” carbon dioxide into glucose, which can then be broken down in respiration to get energy. It’s more or less equivalent to making one’s own food. There are different ways of doing this; the most common is C3 photosynthesis, more or less the “normal” pathway. C4 photosynthesis is found most often in tropical plants, and involves some extras added to the C3 pathway to maximize carbon dioxide uptake in environments where the gas’s availability is limited. In both of these pathways, stomata (small openings in plants’ leaves) allow carbon dioxide into the plant.

Crassulacean acid metabolism, or CAM, photosynthesis adds on further to C4. It is found mostly in desert succulents like cacti and jade plants, and in fact was named after the jade plant’s family, Crassulaceae. In CAM photosynthesis, the stomata open only at night, when the temperature is lower and the water within the plant will evaporate less than it would during the day. The plant then takes in carbon dioxide, fixes it to an intermediate molecule, malate, and stores it to be processed during the day. This cool adaptation helps cacti and succulents survive in their desert environment.

One more note: I haven’t said anything about the first part of the title yet. Well, I’m taking genetics this semester, and I need to do an honors project on a gene that interests me. While poking around for genes involved in drought resistance in plants, I rediscovered CAM photosynthesis, which I learned about a few years ago and thought was really cool. There you are; inspiration from a class project. It really does come from various places.

(My source for this post was The Physiology of Flowering Plants: Their Growth and Development, third edition, by H.E. Street and Helgi Opik.)

Isn’t CAM photosynthesis cool? (If you don’t think so, I totally understand. I know lots of people probably don’t get why I’m a plant nerd.) Have you ever had a jade plant, or a cactus or something similar? If so, what was your experience with it? Tell me in the comments!

My Life This June: In Which I Visit Washington, D.C. and Do More Research and Editing

Hello, everyone! It’s the fourth Saturday of the month, which must mean I’m describing my life this month for you. This June, I went on a family vacation to Washington, D.C., which made me promptly forget about everything else I did this month. . . . I did, however, do some more lab work and writing-related things, which I’ll talk about at the end of this post.

So I was in D.C. (we stayed in Maryland, actually) from Saturday the 11th until Saturday the 18th, which is why I didn’t respond to any blog comments made during that time until I got back. Sorry for the delay, everyone! On the 12th, our first day out doing things, we went to the Smithsonian’s National Zoo, even though it was over 90 degrees outside and the zoo is a very walking-intensive place (from where we parked, you had to go all the way up a giant hill to get to the famous pandas). Despite that, it was a great place to visit! I had only been there once, ten years ago, so it was nice to go again. Below are some of the animals we saw. It was particularly cool to be in some of the exhibits with wild birds loose around us.

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The next morning, we walked around various monuments (since Washington, D.C. is monument land) and passed through the National Gallery of Art’s sculpture garden. This was the first day we passed cool buildings, like the National Archives and the Department of Justice.

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Later that afternoon, we visited the National Gallery of Art itself. This is a great big art museum composed of two buildings; the east wing was designed by famous architect I.M. Pei and is very modernist and cool, while the west wing is a more traditional design. The east wing was a pretty quick tour, since it was under renovation, so we quickly passed under the street to the west wing. This wing was full of beautiful and interesting art, including Ginevra de’ Benci, the only Leonardo da Vinci painting in either American continent, and The Sacrament of the Last Supper by Salvador Dali, my new favorite painting (even though I don’t usually care for Dali’s surrealist work). Anyway . . . here are some more pictures for you.

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On Tuesday, we attended to the actual reason we were in the D.C. area, which was so my brother could compete in the national competition of National History Day. For those who haven’t heard of it, and are junior high or high school students, you should check it out (at the link above). Students compete in the paper, exhibit, performance, website, and documentary categories, as individuals or groups, junior or senior high. I’ve never done it, but this was my brother’s fifth year, and his first attendance at nationals. It was pretty cool to go. Students from different “affiliates” (there were students from places like Guam and South Korea as well as the fifty states and D.C.) traded buttons to try to get all of them, and the different range of projects was pretty interesting. Although my brother did not win any awards at the Thursday ceremony, he still had fun and will do NHD again next year.

On Wednesday, we did a few different things. First, we visited the U.S. Botanical Garden, which was a really neat place, not least because it was the result of George Washington’s vision of a botanical garden in the nation’s capital to educate the populace about plants. (George Washington appreciated plants!) There was a conservatory and some outside gardens. My favorite was probably the orchid collection in the conservatory, although the endangered plants and sensitive plant in the “Plant Adaptations” section were also pretty cool. See the pictures below!

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After the botanic garden, we went back to the National Gallery, since we didn’t see nearly everything on our first run through. We found a few Vermeer paintings and visited the da Vinci and Dali paintings again. After that, we went to NHD night at the Smithsonian American history museum, which is a great place if you ever go to D.C. They have lots of cool stuff, like the ruby slippers Judy Garland wore in The Wizard of Oz, the hat Abraham Lincoln was wearing when he was shot, and lots of first ladies’ inaugural gowns. They also had some NHD exhibits on display that day, so we visited a couple of those as well.

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Thursday and Friday were much quieter. On Thursday, we attended the NHD awards ceremony, then went back to our hotel and hung out. On Friday, we visited the Phillips Collection, which is apparently America’s first modern art museum, mainly to see The Luncheon of the Boating Party by Pierre-Auguste Renoir, a famous Impressionist painter. It was a beautiful painting, and very absorbing; I sat in front of it for a while. They also had other interesting works by modern and contemporary artists, and a lovely little courtyard.

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That wraps up my trip to D.C., and since this is becoming a monster post, I will be brief about the rest of my month. I have continued doing research, spending most of my days in a lab happily analyzing seaweed DNA and growing seaweed spores in a little culture room. I’ve learned a lot of new lab techniques this month, such as the polymerase chain reaction (hugely important in molecular biology). I have also been plugging away at my editing, although I recently made a list of the scenes I have left to edit and realized I am going to have a huge time crunch later next month. (I set a goal of finishing my macro edit by July 31st. We’ll see if that actually happens.) But all in all, it’s been a good month, even the three weeks I wasn’t on vacation.

How was your June? Did you go on vacation this month? If so, where? Have you ever been to Washington, D.C.? (If you live outside the U.S., have you ever been to your nation’s capital, and if so, what was it like?) Have you been to any of the places I visited? If so, what did you think of them? Have you ever done National History Day? (If so, kudos to you! I could never get through all the yearlong work, haha.) If not, does it sound interesting? And lastly, have you been writing or editing this month, and if so, how has it gone? Share in the comments!

 

 

 

Ecology of Certain Forest-Dwelling Members of the Bryophyta; Or, Why Mosses are Underrated

 

Plants are everywhere. As my last semester’s biology teacher put it, you don’t look down from space and see the animals running around; all that green you see is from plants. It is plants. Like this:

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A boreal forest in Canada. (Image not mine)

So in this week’s science post, I want to talk about plants, but not those plants in the picture above. Instead, I want to talk about these:

These “plants” are all examples of boreal feather mosses. And I am here today to tell you a bit about their ecology, in order to illustrate why mosses like these beauties are sadly underrated.

In the northern boreal forest (like the Canadian one shown above), these mosses have to compete with various vascular plants (which have internal water- and nutrient-carrying systems, a bit like an animal’s veins and arteries). But the mere fact that mosses have no vascular systems gives them an edge over vascular plants when it comes to photosynthesis (which is how a plant makes its own food). Let me explain.

If you picked a leaf off a vascular plant (like one of the trees shown above) and looked at it under the microscope, you would find a whole bunch of tiny little holes, called stomata. Stomata open and close to allow the plant to absorb the carbon dioxide it needs for photosynthesis without losing much of the water it also needs for photosynthesis.

But mosses have no stomata; their entire bodies can just absorb as much carbon dioxide and water as they need. So a moss that lives in a “sunfleck” on the forest floor, one of those shifting spots of sunlight amidst the shade cast by the trees, can react better when the sun moves and casts light (also needed for photosynthesis) across that spot than a vascular plant, which has to take the effort of opening its stomata, could.

Boreal mosses are also important for succession; this is when something disturbs the ecological community and the members of the community (the different species that live there) must react. When a tree falls down, for example, it disturbs the plant community around it. Mosses and their relatives have been found to move back in sooner than other plants. This is probably because they have more varied reproduction methods than vascular plants; they readily reproduce asexually, which makes them able to colonize new areas quickly. Here, again, they have an advantage over vascular plants.

Mosses can also compete with vascular plants in a more direct way than those described above. In New Zealand, eleven moss species have been found to have allelopathic effects on plants, including native trees. (In allelopathy, one plant secretes chemicals that actually inhibit the growth of another plant.) Specifically, these mosses’ secreted chemicals inhibit the germination and root growth of other plants. This makes them better able to compete in the crowded New Zealand forest.

 

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Dendrohypopterygium filiculiforme, an allelopathic moss species. (Photo not mine)

So, to wrap up this long blog post, mosses are both pretty and interesting. They’ve adapted in ways that allow them to compete with vascular plants, such as speedy photosynthesis and growth-inhibiting chemicals. They’re also important for succession after forest disturbances like treefall. Altogether, these simple plants are interesting, important, and very underappreciated.

Tell me in the comments: What did you think of mosses before? What do you think now? Do you find these snippets of moss biology as interesting as I do? Did you understand everything I said, or did I use too many technical terms?

Also, if you are curious enough to brave a couple peer-reviewed articles today, here are my references!

Jonsson, B.G., and P.-A. Esseen. 1998. Plant colonisation in small forest-floor patches: importance of plant group and disturbance traits. Ecography 21: 518-526.

Kubásek, J., T. Hájek, and J.M. Glime. 2014. Bryophyte photosynthesis in sunflecks: greater relative induction rate than in tracheophytes. Journal of Bryology 36(2): 110-117.

Michel, P., D.J. Burritt, and W.G. Lee. 2011. Bryophytes display allelopathic interactions with tree species in native forest ecosystems. Oikos 120: 1272-1280.