Love notes of genetics and physiology for Valentine’s Day

A St. Valentine meme compliments of my "friend" the self-styled Rev. Apostle, and Bishop to the Stars, Joel L. Watts.
A St. Valentine meme compliments of my “friend” the self-styled Rev. Apostle, and Bishop to the Stars, Joel L. Watts.

Ahhh….’Tis the time of year when we celebrate romantic love in homage to a 3rd Century priest who came up a head short for performing unsanctioned Christian weddings.  (It is also of note that St. Valentine, or Valentinius as his friends called him, is the patron saint of bee keepers but, strangely, not of birds, flowers, or trees).

In celebration, many suitors, partners, spouses, fling-seekers, and woo-wishers will flock to florists, grocery floral counters, and even gas stations to purchase flowers, namely roses, that have likewise been beheaded.

Those roses, with all of their tightly wound petals, look nothing wild-type roses. Modern roses are the product of many centuries of breeding that started independently in China and the Mediterranean region.

So if the wild-type rose has a single row of five petals, how do breeders get all of those extra petals?  They can just come from nowhere, you know.

The simple answer is that tissue that turns into stamens in the wild-type flower are converted to petal tissue.  While early (and even contemporary) plant breeders may not understand the mechanism responsible for the doubling (gene expression), research is showing that the same gene is responsible for the doubling in both the Chinese and Mediterranean set of species/subspecies.

In a nutshell, what happens is that the different regions of the flower – sepals, petals, stamens, carpel – develop in response to the expression of a set of genes.  It isn’t just the genes acting alone, though; it is their interaction in the tissues that makes the difference.  These genes are grouped by the floral part they affect and are grouped as A-Function, B-Function, C-Function, and E-Function.

If you want to learn a whole lot more about it than I can ‘splain (it has been a few years since my last plant physiology class), this paper thoroughly explains the gene expression and evolution of the flower.  Their figure depicting the flower model is informative, yet simple.  I’ve included it (and its accompanying caption) below.

The ABCE model of floral organ identity. Sepals are produced where A function acts alone, petals where A and B functions overlap, stamens where B and C functions combine, and carpels where C function acts alone. In the eudicot genetic model Arabidopsis thaliana, APETALA1 (AP1) and APETALA2 (AP2) are the A-function genes, APETALA3 (AP3) and PISTILLATA (PI) together specify B function, C function is specified by AGAMOUS (AG), and multiple SEPALLATA genes provide E function
The ABCE model of floral organ identity. Sepals are produced where A function acts alone, petals where A and B functions overlap, stamens where B and C functions combine, and carpels where C function acts alone. In the eudicot genetic model Arabidopsis thaliana, APETALA1 (AP1) and APETALA2 (AP2) are the A-function genes, APETALA3 (AP3) and PISTILLATA (PI) together specify B function, C function is specified by AGAMOUS (AG), and multiple SEPALLATA genes provide E function.  http://www.pnas.org/content/107/52/22570

 

In the paper “Tinkering with the C-Function: A Molecular Frame for the Selection of Double Flowers in Cultivated Roses” researchers show that in lines from both regions of the world produced double flowers as a result in a reduction of expression of the C-Function gene AGAMOUS (RhAG) leads to double flowers.  In Arabidopsis (every plant lab bench jockey’s favorite model plant), this reduction shifts expression of the A-Function genes toward the center of the plant, turning stamens into petals and carpels into sepals.

Now, one question I get from time to time is “why don’t these roses smell like the old-fashioned roses?”  One answer is that as we breed for looks, we are breeding out genes responsible for scent oil production.  So Shakespeare was actually wrong when he said that “a rose by any other name would smell as sweet.”  That isn’t true these days.

So, I wish you a perfectly lovely Valentine’s Day, no matter how you celebrate. Just remember to whisper sweet nothings of floral gene expressions in your sweetheart’s ear.  And remember to stop and smell the roses – if it is a variety that has a decent scent.

Allelopathy Helps Black Walnuts Compete

A walk through the woods can be one of the most peaceful and calming experiences — a place where you can find quiet for reflection and marvel at the beauty of nature. Little do most people know that some plants, especially one specific tree, wage chemical warfare against other plants to keep away potential neighbors that would compete for nutrients and sunlight. In the Appalachian Mountains, the tree most skilled at chemical warfare is the black walnut.

The black walnut tree (Juglans nigra) is a useful, yet often misunderstood tree. Prized for its excellent wood qualities for lumber and furniture, the nuts it produces are either loved or reviled by those who try them.

The flavor of black walnuts is hard to describe. I would say that they have an almost astringent flavor, mainly due to the high level of tannins in them. They aren’t my favorite, but I don’t mind them either. I’ve learned to accept them, unlike during my childhood when you knew which church lady’s cake to avoid at the potluck because you knew that she put black walnuts in everything she baked.

My appreciation for black walnuts grew the year that I was the official nut judge (no joke) for the Black Walnut Festival in Spencer, WV. It was quite an experience — examining and weighing all the entries with a team of high school FFA students who cracked more than a few inappropriate jokes about the situation.

You could tell when someone was picking or cracking black walnuts, thanks to the tannin stains on their hands that just wouldn’t wash off. Black walnuts are a tough nut to crack (literally), so I also remember my grandmother cracking them “the easy way.” She would just pile them up in the driveway and run over them a time or two with her behemoth of an Oldsmobile (you know, the one that had full seats front and back and could hold half the neighborhood).

Black walnut trees have the interesting ability to excrete a chemical called juglone, which makes it nearly impossible for a number of plants to grow anywhere in its root zone. Juglone works by damaging the tiny root hairs on roots that are responsible for taking up a great majority of the water and nutrients the plants use. Research shows that it also interferes with the interaction of the roots with mycorrhizal fungi that aid the plant in taking up nutrients.

This process is not just specific to black walnuts. There are several other plants that do this. The phenomenon, called allelopathy, occurs when an organism excretes something that inhibits the growth of other things around it. You could equate it to the Penicillium fungus excreting a chemical that kills bacteria around it. We harness that chemical to use as penicillin.

Some plants are especially sensitive to the chemical. Many vegetable plants, especially tomatoes, are sensitive. Some plants, mainly those that would grow wild in the woods, are not susceptible. Many grasses also have a hard time growing beneath black walnut trees (tall fescue and Kentucky bluegrass being the exception, except during periods of drought).

Publication with lists of plants tolerant and damaged by juglone

All parts of the tree produce the juglone chemical, so the effects could spread beyond the perimeter of the tree from fallen leaves and branches. I would also suggest that you make sure any fresh woodchip mulch that you use (specifically that from local tree cutters) is free of black walnut. The juglone may break down after composting the wood chips for six months to a year, but I would still be cautious about its use. The wood will release the chemical, killing susceptible plants for a few years in the area where it is applied. Studies suggest that juglone will break down during the composting process, but I would check to make sure by starting a few tomato seeds on the batch of compost to see what happens.

—Garden Professor John Porter is a county extension agent for West Virginia University and writes the weekly Sunday garden column for the Charleston Gazette-Mail Newspaper.  This article was originally published October 2, 2015.

You can find John’s writing at wvgardenguru.com and on Facebook and Twitter.

“Lazy” corn and gravitropism

Inspired by Linda’s post about thigmomorphogenesis, I decided today I would add the word gravitropism to your vocabulary. It simply means growth in response to gravity. Shoots of plants grow up, because they are negatively gravitropic, they grow against the pull of gravity, while roots are positively gravitropic and grow down towards the pull of gravity.

And why is that so important? Well… this is what happens when gravitropism is missing.

cornlazyplant

To the left is normal old corn. The plant to the right was not sat on by a raccoon or anything, it simply has a mutation in a gene called lazy plant1. I’m not kidding. That’s the official, scientific name for this gene. Geneticists have fun with their names, though fruit fly geneticists are for sure the kings of silly gene names. This gene got that name because, as you can see, without a functioning copy of that gene, the corn plant no longer can detect the pull of gravity and so flops down in a “lazy” manner.

This corn is just odd, of course, with no real value (though it was fun to grow) but similar mutations are what give us some of the “weeping” or trailing forms of popular ornamental trees and shrubs.

Your new word for the day: thigmomorphogenesis

I just finished reviewing 4 manuscripts for three different journals and boy is my brain fried. My private reactions ranged from “I can’t wait until this one is published!” to “If I were to use sheet mulch this manuscript would be my first choice.” Anyway, it was the latter manuscript that got me to thinking about what can go wrong with experimental design, which brings up today’s word: thigmomorphogenesis.

This is a great word for those who enjoy figuring out word meanings by deciphering the (usually) Greek or Latin roots. (This exercise also helps you figure out how to pronounce it.) We have “thigmo-” which means touch, “-morpho-” which means appearance, and “-genesis” which means beginning. String them all together and you get the phenomenon seen when plants respond to mechanical stimulation by changing their growth pattern and hence the way they look.

Wind direction from the right creates an asymmetric hedge.
Wind direction from the right creates an asymmetric hedge.

You can easily see examples of thigmomorphogenesis in everyday life. Look at a line of hedge plants where the plants on the end are more susceptible to wind movement and brushing by people, animals or vehicles. They are always shorter, aren’t they? Plants subjected to chronic thigmomorphogenic forces are generally shorter than their neighbors and thicker in girth. (For a longer discussion about how thigmorphogenesis works, you can read my online column.)

How does all of this relate to experimental design? Well, think about what happens if you are testing a product that requires applying it to the leaves of plants once a week. Your treatment plants are touched every week. How can you know that any changes in your experimental plants aren’t due to being touched? The way you eliminate this source of variability is by treating all of the plants the same way. When you are applying the product to the treatment leaves, you apply water (or whatever the solvent is for the product in question) to the control leaves. That way thigmomorphogenesis remains just an interesting tongue-twister and not a fatal design flaw in an experiment.

Puya report!

For all five of you that might have paid attention to my posts on the genus Puya (which does in fact rhyme with booyah…thank you my west-coastie friends):

Here’s the update that you’ve been waiting for!

Puya is a horrifically spiny, painful, and hateful genus in the Bromeliad family. Native to the Andes, the fish-hook-like spines snare passing mammals; the rotting flesh provides nutrients to the exceptionally lean soil of the arid steppes on which it sort of grows/becomes grumpier.

Puya flowers once an eon, in a spectacular [but ill-earned] display that turned me to mush, based on a photo in an Annie’s Annuals catalog (see my “eternal gardening optimist” post). Autumn of 2012, I ordered and received one healthy Puya berteroniana in a 4” pot. Heckling commenced.  Overwinters in a 40 F greenhouse, where it was watered once or twice. Summers have been spent on our deck. Osmocote has hopefully provided required nutrients. Expected to kill her within months, as it is SO VERY not native to the verdant and humid Blue Ridge mountains of Southwest Virginia.

Happy and amazed to say Pootie [what was I going to name her? Bert??] is in her 3rd year – continuing to grow, and, AND, captured her very first mammal!

Pooyah!

Okay… so it’s a fluffy stuffed possum, and the dogs dropped it from the deck above. But snagged! You know Pootie got a thrill…

When Plants Attack! (each other)

When you talk about killer plants, your mind may conjure images of a man-eating plant in “Little Shop of Horrors,” insect-eating Venus flytraps or poisonous plants like deadly nightshade.

While all of those scenarios are interesting in and of themselves, what about plants that attack other plants?

I’m talking, of course, about parasitic plants. These plants thrive on stealing nutrients from other plants, either weakening them or, quite possibly, killing them.

Parasitic plants connect themselves to a host plant and siphon off the sugars that plant produces and the nutrients it pulls from the soil. These plants often bend the definition we have in our heads of plants, since they don’t have to behave like other plants that make their own food.

Probably the most well-known (and beloved) parasitic plant is mistletoe. The plant that gives us the warm fuzzies and romantic feelings around the holidays makes its living by feeding off of the trees in which it lives. They don’t talk about that aspect of the plant in all those Christmas songs. It doesn’t kill the tree, but a heavy infestation can weaken a tree and slow its growth.

Indian pipe (Monotropa uniflora). Photo courtesy GP Raymond Eckhart

While they are few in number, there are some parasitic plants you may run into. Another parasitic plant in our part of the world is the Indian pipe (Monotropa uniflora), a white, chlorophyll-free plant that resembles a smoking pipe as it unfurls from the forest floor. Without chlorophyll, it can’t make its own food, so it connects itself to a nearby tree (usually beech) for nutrients.

Another plant, called a beech drop (Epifagus americana), also makes its living in the same manner. A plant called squaw root or bear corn (Conopholis americana), because it resembles an ear of corn growing out of the forest floor, is a parasitic plant that connects with the roots of oak trees.

An infestation of dodder beginning in an annual bed. Photo courtesy Ann Berry.
An infestation of dodder beginning in an annual bed. Photo courtesy Ann Berry.

These plants may cause a little damage to their host plants. This week, though, there seems to be something more sinister afoot. I received two different calls about the same parasitic plant this week, from different parts of West Virginia (one of which came from Ann Berry, associate vice president for marketing and outreach at WVU). It seems that the problem here was with a parasitic plant called dodder (Cuscuta sp.). Despite the name, I assure you that this plant does not dodder around when it comes to feeding off other plants. This plant can severely infect and potentially kill any plant it touches.

 

Seeds of the plant germinate in the soil, so it starts life just like any other plant. Once germinated, though, the seedling has about 10 days to find a host plant to attach to and begin feeding. But this is not left to chance — it seems that dodder is a pretty good hunter. Scientists have determined that dodder can, in a way, sense chemical signals from nearby plants and grow directly toward them.

Dodder is an odd-looking plant, and many people don’t even know to classify it as a plant. It grows in long strings, often without leaves (or only having inconspicuous ones). Different species can be different colors. The one that is most common here is often a yellow-orange color.

cuscuta Haustorium
Dodder, above, inserts a haustorium into its host plant.

Once the dodder touches the soft tissue of a plant (leaves or stems), it inserts a structure called a haustorium into the plant. Haustoria insert themselves into the plants vascular tissue (veins) and siphons off the water, sugars and nutrients. After the connection is made, the dodder plant detaches its roots from the ground and becomes completely reliant upon the host plant. Luckily it has trouble attacking woody plants, so it mainly goes after herbaceous ones.

One connection is bad enough, but the dodder twines its way around the plant as it grows, resembling what some would call “silly string.” Everywhere the dodder touches the host, it sends in new haustoria to strengthen its connection. If other plants are close enough, the dodder will grow outward through the air to ensnare another host. It can easily grow to encompass many plants, covering them completely and eventually strangling them or starving them out.

My advice to both of the callers this week was to remove as much of the plant as possible, as soon as possible. Unfortunately, the plant can regrow from the connections it makes with the host plant, so you often need to remove whole parts of the plant or the whole plant itself. If it has only made one or two connections, you may be able to control it just by removing the dodder from the plant.

Dodder is hard to see on the ground as it germinates, so it is only usually spotted after it has attached and grown on a plant. If you do happen to catch it before it attaches to a plant, cultivating the soil to break it up and removing as much by hand as possible will help. Unfortunately, there is no spray or control method that will kill the dodder without killing the host.

Dodder is definitely a bizarre plant that many have not seen. Keep an eye out for it this year, since it seems to be cropping up in unexpected places. It just goes to show you that sometimes it’s a plant-eat-plant world out there.

This article was originally published 08.09.15 in the Charleston Gazette-Mail.  You can find more article at wvgardenguru.com.