The Life Of The Party

Biology concepts – plant adaptations, osmosis, parthenogenesis

Last week we discussed the biological implications of an old Christmas carol. Today’s post is a hodgepodge of holiday biology, but we can still find some exceptions.

From a distance, spruce, fir, and pine Christmas

trees look similar. The differences are mostly in

the needles, both shape and number.

Christmas trees – There are many different types of trees used for Christmas, but they are all evergreens. This is the reason they were used in the first place. The tradition sprung from old pagan ceremonies that reminded us that spring would come and there would be a rebirth of greenery.

Evergreens have a thick wax coating on their needles (these are actually their leaves). This adaptation, as well as the low surface area of each leaf, helps to reduce water loss during the arid winter.

The resin of evergreens is higher in sugar than in other trees species. This keeps the liquids in the tree from freezing solid during the cold months. The higher sugar content oozes from the bark and at the collars of the branches, and is very sticky (picture Chevy Chase in Christmas Vacation).

Evergreen is a characteristic not a botanical grouping. They tend to photosynthesize all winter long, given enough water and sunlight. In deciduous trees there are hormonal (phytohormonal) signals that induce cleavage of the leaves from the stems (abscission) when there is not enough sunlight to justify making chlorophyll. In evergreens, there is some of this signal present, and pines do lose leaves in the winter, just not all of them. When cut and kept indoors, the abscission signal is increased, and together with the reduced water – all the needles end up on your carpet.

The leaves of cedar Christmas trees

look different from other evergreens.

If you choose a red cedar, just remember

that there is actually no evidence that

they keep moths away.

The groups of trees used for Christmas are members of the conifers – cedar, fir, and pine, and spruce. In general, pines have two or three needles coming from the same place on the twig, while fir and spruce usually have just one. To tell fir from a spruce, try to roll a needle in your fingers; if flat and won’t roll, it is probably a fir, but if it is four sided and can be rolled, it is a spruce. Cedars look different from the other three, they have scale-like leaves and ball cones, and their bark is more splintered.

Christmas cactus – This is a small genus of plants, comprised of two groups, the truncata and the buckleyi. In the wild, they grow on other plants (epiphytic) or on rocks (epilithic). They don’t have leaves, common in cacti, their flattened green stems serve as their photosynthetic elements. They occur in naturally in eastern Brazil, along the coast of the Atlantic Ocean. Those for sale in the U.S. are cultivars, bred for hardiness and different colors, different plants will bloom in red, yellow orange, or pink.

Thanksgiving cactus stem is shown on the

top, while the bottom stem is from a

Christmas cactus.

In Brazil, the cacti are called May Flowers, reflecting the month in which they bloom in the Southern Hemisphere. In the northern latitudes, they flower from November through January, depending on the cultivar. This presented a classic opportunity for commercialization.

You might want to look at your Christmas cactus a little more closely; you might actually have a truncata when you think you have a buckleyi. The Christmas cactus has stem segments that are rounded, with more symmetric points. The flowers hang down low and their pollen is pink. These flowers generally bloom later and these buckleyi cultivars therefore termed the Christmas cactus.

The yellow pollen on the left is characteristic of a Thanksgiving

cactus. The pink pollen of the flower on the right is typical of

the Christmas cactus.

In contrast, truncata cacti have much sharper stem segments. If it hurts to prune your cactus, you may have one of these. The flowers stay closer to horizontal, or even rise up on the plant. The pollen grains are yellow, so there are several ways to tell these plants apart. Perhaps the best way is by the blooming time. The truncata will bloom closer to the end of November. For this reason, they are often called Thanksgiving cacti. Still think you have a Christmas cactus?

Fruitcake – I am an unapologetic fruitcake fanatic. To everyone who isn’t - stop making fun and just send them to me.

Fruitcake! It may be my favorite

holiday treat.

The biology of fruitcake is based on bacteria, or more correctly, the lack of bacteria. The candied fruits used in fruitcake are not just dried, they are preserved. For many centuries, fruits were precious commodities, especially in the winter. The vitamin C and other nutrients were needed for good health, but spoilage kept most people from having them during the colder weather.

Meats were preserved with salt, called curing, since the days of the ancients. Fruits, on the other hand, don’t taste so good when salt cured. It turned out sugar that could preserve fruits just as salt cured meats. Either liquid syrup or crystalline sugar would do the job, but sugar was very costly. Honey could do the job, but not as well, and it wasn’t much more available. Therefore, preserved fruits were a luxury for some period of time.

With the advent of sugar beet production in the Americas in the late 1500’s and the resulting availability of sugar in Europe, there was a candied fruit glut in Europe. It became more common to use them in baking. Italian pannatone, and fruitcakes were common uses.

So how do salt and sugar preserve foods? It all has to do with water. Bacteria need water to survive; if you remove the water, you stop (or at least slow) bacterial growth. An osmotic gradient is set up when cells are placed in high salt (hypertonic) or high sugar environment. If the salt or sugar content is higher outside the cell, it means that the water concentration is higher inside the cell.

In osmosis, water flows from where there

is little solute toward where there is

much solute. In hypertonic solution,

this means water leaves the cell.

Water will flow from areas of high concentration to areas of low concentration, just as the salts and sugars will. This is diffusion, but in the case of water it is called osmosis (Plants That Don't Sleep Well). The solvent (water) and solutes (those things dissolved in the solvent) try to balance their concentrations, so water flows out of the cell and salts or sugars flow in. The result is pandemonium, chemical reactions are not possible under these conditions, and the organism either dies or goes into stasis.

Dehydration by salt and sugar work in several ways. One, removing water through osmotic pressure will turn the bacteria, fungi, and parasites already on the food to dried up corpses by pulling out their water. Second, the lack of water in the preserved food stops bacteria and other microbes that might land on them from propagating; no water, no cell division.

Third, the high salt or sugar concentrations, even with some water present, limits the species of organisms that could grow there. Only a few microbes, called halophiles (hal = salt, and phile = lover) can grow in high salt environments. Similarly, honey is only about 30% water, so not many bacteria can grow in this low water/high sugar environment (but some important bacteria can, so don't give raw honey to infants). Finally, the loss of water in the foodstuffs reduces the oxidation reactions that might take place to age the food. Fats are especially susceptible to oxidation, they go rancid in not too long. The curing of meats slows this process, but is less a problem in fruits due to the low fat content.

Those fruitcakes deserve a little more credit, don’t they? And by the way, fruitcakes are not the doorstops everyone thinks they are, they actually float in water.

Virgin birth – I will only touch on this subject, as the blog will soon be delving into a series of stories on mating and reproduction. There are many species of animal that can give birth to viable young without mating. This is called parthenogenesis (partheno = virgin, and genesis = birth).

In 2005, a komodo dragon in a zoo laid some

eggs. No big deal, except she hadn’t been housed

with a male for 2 years! Apparently, they can

reproduce sexually, or by parthenogenesis if

no males around. This has changed how

komodos are housed in zoos.

Parthenogenesis occurs when the unfertilized egg receives the messages necessary to begin to divide and form an embryo. The offspring have only their mother’s DNA with which to work, so they are all clones and all female. The egg does have two copies of the chromosomes, but this can occur in two ways. If the egg is haploid but undergoes chromosome doubling, the resultant offspring is a half-clone of the mother. But if the egg is produced only by mitosis, with no meiotic event to result in a haploid gamete, then the offspring is a full clone.

Many species use parthenogenesis exclusively, or in response to environmental or population conditions. Whiptail lizards, as well as aphids and some plants, are famous for undergoing parthenogenesis. No cases of mammalian parthenogenesis have been documented in the wild, but stem cells have been developed by parthenogenesis in the laboratory. Anyway, if the Christmas story was going to rely on parthenogenesis, then Jesus should have been a baby girl.

Mistletoe is an evergreen that grows

on other plants. It can draw water

from the host even in winter. It also

draws animals to the tree in winter.

Mistletoe – These are evergreen, hemi-parasitic plants that grow in many parts of the world. They have photosynthetic leaves, so they produce their own carbohydrates and energy, but they rely exclusively on their host tree for water and minerals. The mistletoe roots bore into the host bark and vascular tissue to obtain the water and minerals it needs.

The mistletoe can serve to hurt the host plant, especially if it grows too well, but they can also help the host. Junipers that harbor mistletoes produce more berries than those without. This is due to the large number of birds that come to eat the mistletoe berries; the juniper takes advantage. This makes it hard to determine of the symbiosis of mistletoe/host is parasitism or perhaps mutualism.

As the berry passes through the bird,

it releases sticky cellulose fibers that

help the seed stick to an unfortunately

placed branch.

The name, mistletoe, is not something commonly brought up at a holiday party. From the Old English word, “mistiltan,” the name tells it all. Birds eat the fruit and seeds of the plant and some of them pass through the GI tract unaltered. When excreted (mistil means dung), the sticky seeds may germinate on a limb (tan means branch). Interesting, but try not to mention it over a bowl of holiday punch.

The white berries of the mistletoe played a role in the 18^th century Christmas kissing tradition. In Scandinavia, the maid under the mistletoe could be kissed, but the gentleman had to pull off a berry each time. While the berries were gone, the kissing privilege was lost. 

Next time we will finish our stories on sleep and activity by talking about introduced species. Then we will start a series of posts on the incredible worlds of water and salts in biology. Our fruitcake discussion above may serve as a great introduction, but it is just the tip of the iceberg.

The concepts discussed here will be discussed in more detail in other posts. Resources will be provided on those occasions.

Keeping Your “Ion” The Ball – Salts and Life

Biology concepts – salts in biology, osmotic potential, action potential, transpiration

Dietary salt – crucial for survival;

Veruca Salt – not so much.

In Latin, verruca means wart, so Roald

Dahl was probably trying to tell us something

when he wrote her character into Charlie

and the Chocolate Factory.

We have learned that one of the crucial functions of water in living organisms is to help regulate the salt concentration in and between the cells (Gimme Some Dihydromonoxide). But why do living things require salts? We all know that we must have a source of salt (sal in Latin) in our diet or we die; the Romans gave it so much importance that part of a soldiers pay was to be used specifically for buying salt – his salary.  But what are its functions?

Water tends to flow from where salts are in low concentration (high water concentration) to where salts are high concentration (low water concentration). Just like other molecules, water diffuses to where its concentration is lower (It’s All In The Numbers-Sizes in Nature). Osmosis (osmo = push in Greek) is the special name given to the diffusion of water, for every other molecule it is just called diffusion.

Too much salt is destructive to cells and organisms, so water helps control the salt held in the body. On the other hand, too much water is also bad for living things (water toxicity), so salts help to control the water concentration. Together, this ratio of salt and water inside and outside of the cell leads to a controlled imbalance called the osmotic potential of the cell. Every living thing has systems to maintain this osmotic potential within a small range (osmoregulation, we will discuss this in more detail soon).

The osmotic potential is measured in units

of pressure (bars). It is equal to the amount

of water that will move in response to a

difference in solute concentration across

a membrane.

When in water, sodium chloride (NaCl, table salt) dissociates into Na⁺ and Cl^- ions, and it is these ions, along with K⁺ (potassium ion from KCl) that perform many functions in living organisms. Sodium is 10x more concentrated outside the cell, while potassium is 20x more concentrated inside. The slight difference in the charges of the two ions (and the fact that most Cl^- is outside cells) sets up a membrane potential in cells.

An important function of this membrane potential is in the neuron (nerve cell), as rapid reversal of the potential along the cell membrane (through ion specific channels) produces an electrical current that we know as the action potential (neural impulse). It is the rapid change in concentrations of Na⁺ and K⁺ cations (positively charged ions) inside and outside of the neurons that sends the messages from our muscles to our brains and back, as well as all the thought processes in our brain.

The action potential of the neuron is not simple.

Sodium is higher outside and potassium is higher inside.

When a signal is received (usually from another neuron),

sodium leaks in and potassium leaks out. The slight

difference in the the charge of each means that the neuron

goes from -70 mV to +40 mV. This depolarization travels

down the neuron’s membrane for the entire cell.

Salt's importance is illustrated when their concentrations get out of whack. Too little salt produces symptoms similar to dehydration, with cramping, nausea and confusion. Too much salt results in hallucinations and insanity. The classic example of too much salt intake is being lost at sea. Not having a supply of freshwater, people may start to drink seawater. The salt concentration is too high; their kidneys can’t get rid of all the excess, and the action potentials in the brain begin to misfire. People will see things that aren’t there, and will make critically bad decisions. Many end up swimming away from relative safety and subsequently drown.

We can get rid of some salt through our skin. Is your dog is happy to see you when licking your face after you arrive home, or does he just want the salt? Athletes will often eat bananas to augment their potassium stores and keep the cramps away after exercising. They should really follow that run with a bowl of lima beans; they have much more potassium.

However, munching on black licorice is alot like running a long distance. Glycyrrhizin is the main glycoside (a sugar bound to a non-carbohydrate) in licorice root and is 20x sweeter than sucrose. Glycyrrhizin prevents potassium reuptake in the kidney, so you end up urinating out most of your potassium stores. You could cramp up due to excessive snacking.

The source of glycyrrhizin’s effect on potassium reuptake has to do with cortisol, a stress hormone. Cortisol is converted to cortisone, but glycyrrhizin inhibits this conversion. The increased cortisol makes it appear like your body has too many salts in the blood, and you adjust. This isn’t just a problem for the people who eat a lot of licorice.

A 2010 study indicates that pregnant women who eat licorice can permanently affect their children’s hormone control in their brains. The hypothalamic-pituitary-adrenocortical axis (HPAA), is a relay that controls the child’s production of cortisol, aldosterone and other hormones. These work to control the osmotic potential of the blood and therefore the blood pressure (as well as other things).

The researchers data shows that maternally ingested licorice inhibits the fetal barrier to maternal cortisol. More cortisol then passes to the fetal blood system, and programs the HPAA to have a higher baseline. From then on, the babies make more cortisol, a stress hormone that puts pressure on the physiology, sodium and potassium levels, and can lead to weight gain. Moms – take care – what you eat does affect your baby.

Na⁺ and K⁺ work in muscle function; cramping and paralysis may result from too little or too much salt. Your heart is a muscle, so changes in salt concentration in the cell can cause heart attacks as well. Many a mystery movie has included the injection of potassium chloride to induce a heart attack. Sodium and potassium cations help maintain proper blood pressure, proper acid/base levels, and proper movement of carbon dioxide from the blood to the lungs. There are precious few functions in which these positive ions don’t play a role.

Collagen and elastin help to make your skin and

joints pliable. O.K., maybe not this elastic – this is

the result of Ehlers-Danlos syndrome, which is

often a genetic disease.

When we think of salt, we usually think of table salt (NaCl), but there are more functions for K⁺ than there are for Na⁺, and it is present in higher concentrations in the cell. Potassium is important for the formation and crosslinking of collagen and elastin proteins. These connective tissue proteins hold all your tissues together; they keep your skin from tearing when someone pokes you in the arm, and allow your lungs to expand without ripping when you inhale. So K⁺ is pretty important even when not working with Na⁺. It is interesting then that potassium is the only major mineral nutrient for which there is not a recommended daily allowance.

Remember that we often take in these salts as NaCl or KCl. Does the Cl^- play a role in organism function? – you bet it does. Chloride anion (a negatively charged ion) is used to produce the hydrochloric acid (HCl) that breaks down the food in our stomachs. Chloride also works in the immune system, hypochlorite (the same active molecule as in bleach) in the white blood cells helps to kill infectious agents and activates other immune system molecules. Chloride is required for the uptake of vitamin B12 and iron and helps control your blood pressure; therefore, Cl^- isn’t just that other ion that comes in with Na⁺ or K⁺ (or Ca²⁺).

Chloride ion is elemental chlorine that has gained one electron. This doesn’t seem like much of a change, but it is the difference between life and death. Chlorine itself is a yellowish green gas and it can kill you in a matter of seconds. Chlorine really wants that extra electron, and it doesn’t care if it has to rip it from your lung proteins to get it. When you breathe in chlorine, it reacts with the water in your lungs to produce hydrochloric acid that eats away the cells. It will also react with almost any carbon-containing molecule and further destroy the lung tissue. It was suggested during the American Civil War that chlorine gas could be useful, but it wasn’t until World War I that it was used as a weapon.

Chlorine is poisonous, but we use it to disinfect drinking water and pools. When diluted greatly in water, chlorine does not have the strongly deleterious effect on our cells as it does as a gas, but can still react with and kill microorganisms. Chlorination of water began in the Chicago stockyards around 1908, when the decaying meat and gut bacteria were getting into the drinking water and making the residents sick. The bleach used to disinfect surfaces is much the same as the chlorine used to disinfect 75% of the drinking water in the U.S.; it’s just there in lower concentration. Now chlorine is used in pools as well, and you know it is working because your eyes get red and sting.

Did you know that plants had openings in their leaves called

stomata? Turgor pressure caused by the flow ions in and

out of the guard cells makes the stomata open or close. Their

shape changes based on the amount of water in the guard cell.

There are no exceptions to the rules of salt requirements (weird, isn’t it). All living things need to take in Na⁺, K⁺, Ca²⁺, and even Cl^-. Plants use potassium and sodium for water balance, especially to bring morphologic changes like the blooming of flowers. These cations, along with chloride, work in the opening and closing of pores in the leaves (stomata) for the uptake of carbon dioxide and the release of oxygen and water during transpiration (Gimme Some Dihydromonoxide), and in the chemical splitting of water during photosynthesis. It seems that other organisms rely on these ions even more than animals.

All bacteria require potassium and sodium for osmotic regulation and cellular activities.

As the concentration of Na⁺ in a bacteria’s environment goes up, its dependence on Cl^- becomes greater. Fungi, protists, and even viruses depend on salts to remain alive, even though viruses are technically not a form of life. Viruses carry nucleic acid, and salts are needed to balance the charges of the DNA or RNA so it can be stuffed into the viral package, a function within the area of molecular biology.

 

Giardia lamblia and other protozoa use salt ions

to control their osmotic potentials and for other

biochemical functions. Giardia can also change

your potassium levels by causing intense diarrhea

after drinking contaminated stream water.

Molecular biology involves replication of DNA, the transcription of DNA to RNA, and the activities of RNA translation to proteins. K⁺, Cl^-, and Na⁺ are involved in all these areas. In a feedback mechanism, salt ions control the switches that turn on genes that then control the levels of the ions. If one ion is too high, it will turn on the genes that code for proteins which remove that ion from the cell. Isn’t evolution nifty?

Tightly regulating salt concentration in the cell is important for life, and we have to drink water (kangaroo rats excepted) in order to stay alive. These are the peanut butter and jelly of biology and we will start to see how they work together next time.


Räikkönen, K., Seckl, J., Heinonen, K., Pyhälä, R., Feldt, K., Jones, A., Pesonen, A., Phillips, D., Lahti, J., Järvenpää, A., Eriksson, J., Matthews, K., Strandberg, T., & Kajantie, E. (2010). Maternal prenatal licorice consumption alters hypothalamic–pituitary–adrenocortical axis function in children Psychoneuroendocrinology, 35 (10), 1587-1593 DOI: 10.1016/j.psyneuen.2010.04.010

For more information and classroom activities on salts in biology, osmotic potential, action potentials, or chloride ion in biology, see:

Salts in biology –

http://www.ext.colostate.edu/pubs/foodnut/09355.html

http://www.physiologymodels.info/contractile/NaK_pump.htm

http://muscle.ucsd.edu/musintro/ecc.shtml

http://www.webelements.com/sodium/biology.html

http://nautilus.fis.uc.pt/st2.5/scenes-e/elem/e01140.html

http://www.youtube.com/watch?v=ntlX5Ve6yj8

http://en.wikipedia.org/wiki/Sodium_in_biology

http://en.wikipedia.org/wiki/Potassium_in_biology

http://www.webelements.com/potassium/biology.html

Osmotic potential –

http://physioweb.uvm.edu/diffusion/pages/OsmPotential.htm

http://h2g2.com/dna/h2g2/A686766

www.mrothery.co.uk/studentswork/.../osmosis%20presentation.ppt

http://biology.clemson.edu/bpc/bp/Lab/110/osmosis.htm

http://biology.kenyon.edu/HHMI/Biol113/movemet%20of%20water%20in%20plants.htm

http://5e.plantphys.net/article.php?ch=3&id=29

Action potential –

http://students.cis.uab.edu/nkm188/project_back2.html

http://faculty.washington.edu/chudler/ap.html

http://outreach.mcb.harvard.edu/animations/actionpotential.swf

http://bcs.whfreeman.com/thelifewire/content/chp44/4402002.html

http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-13/CB13.html

http://www.blackwellpublishing.com/matthews/channel.html

http://teach.genetics.utah.edu/content/

http://faculty.washington.edu/chudler/chmodel.html

http://science.education.nih.gov/supplements/nih2/addiction/guide/lesson3-1.htm

http://www.accessexcellence.org/MTC/96PT/Share/conley.php

http://www.ywpw.com/cai/software/hhsimu/

Chloride in biology -

http://web.squ.edu.om/med-Lib/MED_CD/E_CDs/anesthesia/site/content/v03/030731r00.HTM

http://muscle.ucsd.edu/musintro/ecc.shtml

http://www.comprehensivephysiology.com/WileyCDA/CompPhysArticle/refId-cp080117.html

http://www.bio.umass.edu/biology/mccormick/Cl_cell.html

http://www.webmd.com/a-to-z-guides/chloride-cl

http://ivy_league0.tripod.com/rhyme_of_the_ancient_wanderer/id101.html

http://labtestsonline.org/understanding/analytes/chloride/tab/test

http://www.livestrong.com/article/277296-sodium-potassium-chloride-in-the-body/

stomata –

http://faculty.washington.edu/ktorii/stomata.html

http://bioweb.usu.edu/kmott/Complexity_Web_Page/Stomata.htm

http://evolution.berkeley.edu/evolibrary/article/mcelwain_03

http://www.geocraft.com/WVFossils/stomata.html

http://www.nature.com/scitable/topicpage/plant-vacuoles-and-the-regulation-of-stomatal-14163334

http://www.biologycorner.com/worksheets/stomata.html

http://www.biologyjunction.com/leaf_stomata_lab.htm

http://uwstudentweb.uwyo.edu/d/dbrouss1/stomate.htm

http://www.biologycorner.com/worksheets/stomata.html

http://www.classtech2000.com/toucan/modules/stomata/stomata.htm

http://www.accessexcellence.org/AE/AEC/AEF/1994/case_leaf.php

http://www.apsnet.org/edcenter/intropp/topics/Pages/OverviewOfPlantDiseases.aspx

Plants That Don’t Sleep Will Take The Dirt Nap

Biology concepts – nastic movements, turgor pressure, evolutionary pressure, tropism, osmosis

If you don’t let a Mimosa pudica (sensitive plant) plant rest at night, it will wilt away to nothing. A plant that needs a good night’s sleep? Really? We have talked about how sleep revitalizes different brain functions, especially within the hypothalamus (The Best Cure For Insomnia Is To Get A Lot Of Sleep), but plants don’t have a hypothalamus or any brain for that matter. So why does it die if it can't rest; is it out of its mind?

The prayer plant on the left is how it looks during the day, but

on the right, the leaves have folded or curled up. They also stand

straight up, as if at attention. A tough way to spend the night, but

it must serve some purpose.

The prayer plant (Maranta leukoneura) folds up its leaves at night and tilts them upward. When morning comes, the leaves tilt back into their day position and unfold to catch as much sunlight as possible. The folded leaves might look like they are praying (hence the name), and it may appear that they are sleeping, but this is just anthropomorphism.

Humans have a need to feel connected to the rest of Earth’s life, and in the process, we tend to see the behaviors of other organisms in human terms, trying to assign some human motivation to them. So, is the plant sleeping? Does it need to rest? No. Sleep in animals implies inactivity and neural rearrangement, and these don’t occur in plants.

Charles Darwin performed crucial experiments

in plant movement in his later life, including the

identification that chemical signals moving in the

plant are responsible for growth toward the light

(heliotropism). Notice that his son got pretty good

billing as an assistant.

However, the fact that the plant carries out this activity every night suggests that it has evolved in response to some pressure, some need. Surprisingly little is known about why plants move their leaves at night, but there are a few hypotheses. Some scientists believe that changing the angle of the leaves helps funnel dewdrops and overnight rain down the trunk or stem to the roots. Charles Darwin published two books on these plant movements, his theory being that the behavior reduced the chance of chill or freezing.

Another hypothesis suggests that leaves fold up to keep the rain from pooling on them and promoting bacterial or fungal growth. Or perhaps, apposing one leaf closely to the opposite leaf reduces the amount of water lost overnight. However, aquatic plants don’t have to worry about loss of water, but some immersed plants, like Myriophyllum Mattogrossense, still fold up at night. It may be a holdover from their terrestrial days, as most of today’s aquatic plants evolved from terrestrial plants.

My personal favorite proposes that by folding up their leaves, the plants give nocturnal predators a better shot at seeing, hearing, and smelling nocturnal prey. By helping the predators, plants are indirectly protecting themselves from animals that would eat them- plants are sly little devils (more anthropomorphism). It is probable that different plants move for different reasons, so one hypothesis almost certainly won’t cut it for all organisms.

Plants have night moves other than folding leaves. Morning glories (Ipomoea violacea) close their flowers overnight. The reasons for this movement may be a little plainer. Dry pollen sticks to pollinators better than wet pollen, so closing off the stigma to rain or dew keeps the pollen dry. It also takes energy to maintain an open flower; this energy would be best spent when pollinators are around. If the plant’s pollinators are diurnal, they why leave the buffet open all night?

Just as animals have an internal clock, plants gauge

their movements according to the circadian period.

Often plants match their rhythms to pollinator animals

they depend on or to avoid the active periods of

predators. Anyway, I like the picture.

There are also flowers that have the exact opposite behavior, opening their flowers as the sun sets. Philodendron selloum (Is It Hot In Here Or Is It Just My Philodendron) is a classic example, with its spathe closing down in the early morning hours.

Moonflowers (Ipomoea alba) are another example.  At about 8:00 pm, the moonflower opens. A single flower can go from completely closed to fully open in less than a minute (http://www.moonlightsys.com/themoon/flower.html). The morning glories and the moonflowers are both of genus Ipomoea, but they have opposite behaviors – different pressures lead to different adaptations, even in closely related species.

These movements of plant structures are independent of the direction of the stimulus, ie. they are not following the sun or being blown by a particularly wind, so they are called nastic movements. Nyctinasty (nyc = night or darkness, nastic = firm or pressed close) is the specific movement of leaves or flowers in a daily pattern, open during the day and closed at night. If directed by the position of a stimulus, the movements are called tropisms (heliotropism, thigmotropism, gravitropism).

The left picture shows that changes in the pulvinus shape could affect the direction of the entire petiole and all the leaves, or individual leaves (like on the sensitive plant). The middle cartoon indicates that filling the central vacuole with water can change the shape of the cell, pushing in one or more directions. The right image shows just how the extensor cells on the bottom must be inflated to lift the petiole, while turgidity in the flexor cells makes the leaf drop.

Nyctinastic movements are accomplished by the flow of water in and out of specific cells in the pulvini (swellings, singular is pulvinus) at the base of the petioles (the stalk that attaches the leaf blade to the stem). It is not unlike our muscle movements in that there is an extensor and a flexor pair. When K+ and Cl- are pumped into the extensor cells on the bottom of the pulvini, they become hypertonic and water follows the ions through osmosis. This causes the extensor cells to swell due to increased turgor pressure.

Turgor pressure refers to the pressure of the cell contents against the cell wall. This increased turgor pressure at the bottom of the petiole pushes the leaf up. In an opposite fashion, night causes a movement of ions to the flexor cells on the top of the petiole. Water flows out of the extensors and into the flexors by osmosis, causing the stem to droop. Flowers and leaves open and close by the same movements, with the extensor and flexor cells located at their bases.

Turgor pressure is the same mechanism which causes the venus flytrap (Dionaea muscipula) to snap closed its jaws of death when an insect disturbs its trigger hairs. These hairs are located on the nectar laden, red lobes of the trap. Touching just one trigger hair doesn’t spring the trap, two must be displaced within 20 seconds of each other. This saves energy and unnecessary trap closings; each trap snaps shut only four or five times, then dies. If you thought the moonflower moved fast, check out the venus flytrap (http://www.youtube.com/watch?v=ymnLpQNyI6g). I’m just surprised we can’t hear the water shooting into the flexor cells!

The venus flytrap supplements its diet of water and carbon

dioxide with proteins from the insects it catches and digests.

The bright surface with nectar draws them in, where they trigger the

mechanosensor hairs. The magnified image on the right shows a

trigger hair with its hinge that transmits a signal to the pulvini to

swell quickly and snap the trap shut.

The trigger hairs are mechanosensors. The stimulus that trips the trigger and causes the flow of ions and water in the extensor and flexor cells of the hinge region is directionally irrelevant; therefore, the snapping shut of the trap can be considered a nastic movement. In this case, as with the sensitive plant (Mimosa pudica), the movement is called haptonasty (hapto = touch).

A small percentage of plants have nyctinastic movements, so they are an exception to the rule that plants don’t move actively, but even a small percentage means that thousands of species do have these movements. This many exceptions underscores the point that nyctinasty must perform an important function.

Just as humans with fatal familial insomnia die from a lack of sleep (An Infectious, Genetic Disease), the sensitive plant has a much shorter lifespan when nyctinasty is prevented. A plant hormone that stimulates leaf opening was identified in 2006. When given to plants continuously, it caused the leaves to remain open. When nyctinasty was prevented in this way, the leaves were noticeably damaged within a few days, and the plant was dead in less than two weeks. It may not be sleep, but whatever it is, it is just as important.

Some plants are open during the day and some are open at night, just as some animals are active during the day and some during the night. And just as plants adapt to a time schedule to promote survival, animal adaptations are crucial to life in the light or the dark. But that doesn’t mean that some organisms won’t throw us a curve, as we will discover next time.

Ueda, M., & Nakamura, Y. (2006). Metabolites involved in plant movement and ?memory?: nyctinasty of legumes and trap movement in the Venus flytrap Natural Product Reports, 23 (4) DOI: 10.1039/b515708k

For more information, classroom activities or laboratories on nastic movements or turgor pressure, see:

nastic movements –

http://plantsinmotion.bio.indiana.edu/plantmotion/movements/nastic/nastic.html

http://sci-wikibook.bacs.uq.edu.au/?q=content/8-2-5-nastic-movements

http://www.biologie.uni-hamburg.de/b-online/e32/32.htm

http://www.tiem.utk.edu/~gross/bioed/webmodules/nasticmovements.html

http://dennis-holley.suite101.com/nastic-movements-in-plants-a129827

http://seedsaside.wordpress.com/2007/02/18/word-of-the-week-nyctinasty/

http://abstracts.aspb.org/pb2011/public/P19/P19066.html

http://amirshahrokhi.christopherconnock.com/tag/haptonasty/

http://bottleworld.net/?p=38

http://www.wiziq.com/tutorial/33908-2-How-Plants-grow-and-move

www.the-aps.org/education/k12curric/activities/pdfs/watson.pdf

http://www.actionbioscience.org/education/hershey3.html

turgor pressure –

http://5e.plantphys.net/article.php?ch=t&id=387

http://mayaanjali.hubpages.com/hub/Determination-of-turgor-pressure-and-study-of-the-process-of-osmosis

http://sci-wikibook.bacs.uq.edu.au/?q=content/4-2-5-turgor-pressure-controlling-ion-flow

http://biology.kenyon.edu/edwards/project/steffan/frames/turgor.htm

http://www.practicalbiology.org/areas/advanced/exchange-of-materials/osmosis/observing-osmosis-plasmolysis-and-turgor-in-plant-cells,66,EXP.html

http://www.bigsiteofamazingfacts.com/why-do-flowers-close-up-at-night

http://www.scientificameriken.com/yr2/flower.asp

http://www.biology-online.org/11/8_water_in_plants.htm

http://www.biologie.uni-hamburg.de/b-online/e32/32f.htm

http://www.letstalkscience.ca/educators/hands-on-activities.html?sobi2Task=sobi2Details&catid=8&sobi2Id=9

It’s Not Just Chili Peppers That Are Hot

Biology concepts – cinnamaldehyde, nasal hyperreactivity, piperine, allyl isothiocyanate, eugenol, gingerol, tinyatoxin, osmotic stress, agonist/antagonist

The last few years have seen the rise and fall of The Cinnamon Challenge. I can’t tell you why it came, but I can explain why it went. And the reason relates to the capsaicin receptors we have been talking about.

Don’t think cinnamon candy can be hot. Your unbearably hot

cinnamon bears from Jelly Belly and your Atomic Fireballs are

both flavored with cinnamon oil. Fireballs have been around

since the 1950’s which explains the atomic reference. It takes

over two weeks to make one. Cinnamon is not ranked on the

Scoville scale because the main spicy compound is

cinnamaldehyde, not capsaicin. But there is some capsaicin in

cinnamon oil, so I think it could be ranked without breaking

some long standing policy.

The challenge goes like this: you take one tablespoon of cinnamon and try to swallow it all in 60 seconds without any water. If any one tells you they did it and came out O.K., they’re lying. If you see video of someone doing it easily, it's been faked.

Here’s how the challenge works for everyone. The compounds in cinnamon stimulate a coughing reflex (explained below). When you cough, you expel air and you have a compulsion to inhale. Here’s where the trouble starts. The inhalation carries a good portion of the cinnamon powder down your trachea and into your lungs.

Now you’ve done it. The ensuing coughing fit can be powerful enough to break ribs. The compounds in the cinnamon immediately begin to burn your lungs, make your eyes water, make your nose run, and increase your breathing rate. More inhalations carry more cinnamon into your lungs and the burn intensifies. YOU WILL blow it out, spit it out, vomit it out. The pain in your lungs will likely last for three weeks or more. Sounds like fun, doesn’t it?

Here’s the biology of the why it ends well for no one. Cinnamon contains compounds called cinnamaldehyde and eugenol, as well as capsaicin (much lower amount). The capsaicin and eugenol activate TRPV1 ion channels. Cinnamaldehyde is a different class of molecule from the capsainoids, so it does not activate TRPV1, but it does activate a powerful member of another subfamily, TRPA1. We will talk more about this receptor in later posts.

TRPV1 is involved in cough reflex, runny nose, and in the burn that the follows the challenge. The TRPA1 activation causes powerful pain in the lungs and trachea. Together, these compounds result in the involuntary cough, reflexive inhalation of cinnamon into the lungs, and all the pain that follows from activating the TRPV1 pain receptors in your lungs. Now you know WHY you should avoid the challenge.

Asthma is a trigger for airway or nasal hyper-reactivity.

It is easy to see how this could get out of hand, especially

when it can lead to chronic inflammation and damage of

the airway tissues. And to think, it is mediated in part by

the same receptor that makes your Sunday afternoon

chili stew spicy.

Don’t laugh at the portion of the response that takes place in your nose. My mother-in-law got some chili pepper oil up her nose once, and she still refuses to be in the same room as a chili. Her runny nose, sneezing, and watery eyes were directly due to the capsaicin. But for some people it happens for no reason. This is called nasal hyper-reactivity.

In some cases the exaggerated nasal response is due to an allergen, but in other people the trigger is unknown. The TRPV1 ion channels in the nasal mucosa may be over-expressed (too many of them). Their activation brings mucous, bronchoconstriction, cough, and sneeze.

The evolutionary strategy here is like with the cinnamon. Your body is trying to keep toxic or harmful substances out of your lungs. A new study has linked nasal hyper-reactivity to TRPV1 action alone, without need of other receptors. What is more, the paper identifies a new TRPV1 antagonist. An antagonist is a molecule that binds to the receptor but does not activate it, and it can prevent the receptor’s stimulation by molecules that would normally activate it (agonists).

This new antagonist of TRPV1 can suppress the nasal hyper-reactivity and give some relief those afflicted. You may think nasal hyper-responsiveness is trivial, but it’s snot – get it? It’s snot.

Nasal hyper-reactivity is often diagnosed by assessing an exaggerated response to capsaicin in the nose. I can’t imagine how any response to nasal capsaicin could be considered exaggerated. It’s just lucky for us that capsaicin isn’t volatile. Less of it gets into the air because it has a long hydrocarbon tail. 

Because it isn’t volatile, capsaicin doesn’t have an odor, not until you chew it and volatilize it yourself into your nose do you know you’re in trouble. The runny nose is your body recognizing there is something there that you really don’t want in your lungs. It’s bad enough with cinnamon, can you imagine getting capsaicin in your lungs?

The capsinoids are a group of compounds within the

vanilloids. You can see the resemblance to vanillin, so

there are all vanilloids. The different capsinoids are all

found in chili peppers, but capsaicin is the most

abundant and potent, but the structures of the different

capsinoids are very similar.

Pure capsaicin ranks at 16 million Scoville heat units (SHU). But it isn’t the  only capsinoid in chili peppers. There is also dihydrocapsaicin (15 million SHU), nordihydrocapsaicin (9.1 million SHU), homocapsaicin (8.6 million SHU), and homodihydrocapsaicin (8.6 million SHU). Each of these can activate TRPV1 to bring the burn. But it doesn’t stop there; many other compounds can bind to TRPV1 as well. Here's some of them:

Piperine (100,000 SHU) is the spicy compound in black and white peppercorns. You already know black pepper is spicy, and it activates TRPV1 just like capsaicin. Remarkably, it's even more efficient than capsaicin at opening the TRPV1 ion channel. However, it's found in lower amounts that capsaicin in most chilies and has a greater ability to desensitize TRPV1, so it burns less. We will talk about desensitization of TRPV1 in the coming weeks.

Allicin is found in garlic and onions; they can burn too. Raw garlic is especially pungent; try it some time. Garlic is used in many folk medicines – it has been show to prevent or treat fungal infections, lowers blood pressure, is neuroprotective, and can slow the growth of some cancer cells. Some of these effects are mediated by TRPV1. Oh, and it wards off vampires too.

Eugenol is found in many foods, including cinnamon, bay leaf, clove, and allspice. It activates TRPV1, but like piperine, it can be desensitizing too. For this reason, eugenol has a numbing effect and is often used in dental preparations. If you have ever had a cavity filled with the silver amalgam, you probably smelled cloves in the process - that was the eugenol. Just recently it has been shown that eugenol also activates TRPA1 pain receptor, so maybe the dentists should be rethinking their strategy.

Radishes, horseradish, wasabi, and mustard contain allyl isothiocyanate (AITC). This compound binds to both TRPV1 and TRPA1, so they can generate a lot of pain, and the heat sensation as well. In mustard seeds, the AITC isn’t produced until the seeds are broken and an enzyme is released that converts one compound into AITC. This is why stone ground mustards with larger chunks of seeds are less spicy.

In the horse trade, a raised tail means a younger, livelier

horse. When someone wanted to sell an old, worn out

horse, but get more money, they might put a piece of

ginger in the anus of the horse. The burn from the

gingerol would make it raise it’s tail. It has also been

used in horse shows, but is now illegal. Oh yes,

sometimes “gingering a horse” also involved live eels.

The spicy compound is not stored in the plant as AITC because it's harmful to the plant as well. Only when an herbivorous predator comes along and starts munching on the plant is the toxic chemical produced. A new study (2013) shows that AITC actually makes TRPV1 more sensitive to heat, so using wasabi with hot food will really crank up the pain.

Ginger contains gingerol (60,000 SHU), but when you cook it gingerol is converted to the sweeter and more aromatic form called zingerone. Both can activate TRPV1.  There is also gingerol in mustard oil, so both mustard and ginger have been used in folk medicine, like plasters they use to slather on wounds. For a less appropriate use of ginger, see the photograph at the right.

Camphor is used in things like Vicks VapoRub. It activates TRPV1, so you feel warm, but it can also activate a cool receptor, so it seems to open up your nose. We will have much more to say about this in a couple of weeks. Found in certain trees, camphor is slightly analgesic (pain killing), and is antimicrobial, so it does serve a purpose in Vicks.

In addition to these plant-based agonists, TRPV1 is activated by other things as well. We already talked about how the channel is opened by acid (excess protons), but it can be activated by inflammation in tissues and some endogenous pain killers as well, like the endocannabinoids we talked about at New Year’s.

Tinyatoxin (and resiniferatoxin for that matter) are

produce by the Euhorpbia poissonii plant. Native to Nigeria,

its extract is used by natives as a pesticide. The tinyatoxin

and resiniferatoxin are neurotoxic and can kill TRPV1-

expressing neurons, so they are being looked at as a

way to treat chronic pain.

There are artificially produced agonists as well. Resinferitoxin activates the heat receptor TRPV1. It rates 108.8 billion on the Scoville scale! Scientists are trying to find a use for it in chronic pain and other diseases (more in two weeks). There is also tinyatoxin from the Euphorbia plant. It is slightly less spicy, about 5.3 billion SHU. It is a neurotoxin and can kill you in large amounts.

One last agonist for TRPV1 – osmotic stress. This refers to the movement of water out of cells (so they shrink) or into cells (so they swell) when there is an imbalance of salts inside and outside of the cell. Too much salt in the extracellular fluid is called hypertonic, and water will flow out of cells and toward the more concentrated salts. Too little salt in the extracellular fluid is called hypotonic and water will move into the cells where the salt concentration is higher.  We want an isotonic environment, where the slat is the same in and out of the cell.

TRPV1 sense osmotic changes, specifically hypertonicity. A 2010 paper shows that there is a TRPV1 in the brain that does not react to heat or capsaicin, but does respond to osmotic stress. TRPV1 sense cell shrinkage and signals the hypothalamus of the brain to release a hormone called vasopressin (also called ADH). This hormone causes more water to be retained and more salt to be excreted, This lowers the salt concentration outside the cells and the cell shrinkage can be corrected.

Osmotic pressure is related to the amount of water versus the

amount of salts in the water. In the cartoon, the salts are

represented by the blue spheres. Water will travel to wherever

salts are highest, because that means water concentration is

lower. Hypertonic means water will flow out of cells, while

hypotonic means water will swell the cells, even to the point of

lysing them. The representative cell is a red blood cell, since

they are very susceptible to osmotic changes.

Another receptor of the same subfamily, TRPV4, senses swelling during hypotonic crises. This then triggers the hypothalamus to release less vasopressin and the salt concentration will increase outside the cell; excess fluid in the cell will flow out of the swollen cells. A 2011 paper shows that TRPV1 works only on shrunken cells and TRPV4 only on swollen cells.

Using TRPV1 in osmoregulation makes sense. It is closely related to thermoregulation, considering how you use sweating to get rid of excess heat. Sweating messes with osmotic pressures. Nature is smart that way.

Next week, more functions of TRPV1 – it can make pain worse and stop pain. How can that be?

Holland C, van Drunen C, Denyer J, Smart K, Segboer C, Terreehorst I, Newlands A, Beerahee M, Fokkens W, & Tsitoura DC (2013). Inhibition of capsaicin-driven nasal hyper-reactivity by SB-705498, a TRPV1 antagonist. British journal of clinical pharmacology PMID: 23909699

Chung G, Im ST, Kim YH, Jung SJ, Rhyu MR, & Oh SB (2014). Activation of transient receptor potential ankyrin 1 by eugenol. Neuroscience, 261, 153-60 PMID: 24384226

Alpizar YA, Boonen B, Gees M, Sanchez A, Nilius B, Voets T, & Talavera K (2014). Allyl isothiocyanate sensitizes TRPV1 to heat stimulation. Pflugers Archiv : European journal of physiology, 466 (3), 507-15 PMID: 23955021

Ciura S, Liedtke W, & Bourque CW (2011). Hypertonicity sensing in organum vasculosum lamina terminalis neurons: a mechanical process involving TRPV1 but not TRPV4. The Journal of neuroscience : the official journal of the Society for Neuroscience, 31 (41), 14669-76 PMID: 21994383

Sudbury JR, Ciura S, Sharif-Naeini R, & Bourque CW (2010). Osmotic and thermal control of magnocellular neurosecretory neurons--role of an N-terminal variant of trpv1. The European journal of neuroscience, 32 (12), 2022-30 PMID: 21143657

For more information or classroom activities, see:

Agonist/antagonist –

http://www.biopsychology.com/6e/activity0403.html

http://biowiki.ucdavis.edu/Biochemistry/Transport_and_Kinetics/Enzyme_Inhibition/Agonist_and_Antagonist_of_Ligand_Binding

http://forums.studentdoctor.net/threads/understanding-antagonist-agonist-drugs.1005095/

http://employees.csbsju.edu/hjakubowski/classes/ch331/transkinetics/olinhibition.html

Eugenol –

http://pubchem.ncbi.nlm.nih.gov/summary/summary.cgi?cid=3314

http://www.nlm.nih.gov/medlineplus/ency/article/002647.htm

http://mentalfloss.com/article/12297/why-do-all-dental-offices-smell-same

http://www.ewg.org/skindeep/ingredient/702373/EUGENOL/

http://chemistry.about.com/od/factsstructures/ig/Chemical-Structures---E/Eugenol.htm

http://www.motherearthliving.com/plant-profile/eugenol.aspx

Gingerol –

http://www.whfoods.com/genpage.php?tname=foodspice&dbid=72

http://books.google.com/books?id=5WY08iuJyawC&pg=PA86&lpg=PA86&dq=gingerol&source=bl&ots=1LwF_y9UUy&sig=-phjWzpMtWo8-QbJ-RDayDgxZUg&hl=en&sa=X&ei=BhUEU67SBafuyQHFhYDYAw&ved=0CDYQ6AEwBTgK#v=onepage&q=gingerol&f=false

https://www.acs.org/content/acs/en/molecule-of-the-week/archive/molecule-of-the-week-gingerol.html

http://rucore.libraries.rutgers.edu/rutgers-lib/21328/

camphor -

http://www.webmd.com/vitamins-supplements/ingredientmono-709-CAMPHOR.aspx?activeIngredientId=709&activeIngredientName=CAMPHOR

http://www.botanical.com/botanical/mgmh/c/campho13.html

http://plants.ifas.ufl.edu/node/101

http://www.chemie.fu-berlin.de/chemistry/oc/terpene/campher_en.html

http://www.drugs.com/cdi/camphor-ointment.html

http://www.ipm.ucdavis.edu/PMG/GARDEN/PLANTS/camphor.html

tonicity –

http://www.phschool.com/science/biology_place/biocoach/biomembrane1/solutions.html

http://www.youtube.com/watch?v=_slUL3kMZlU

http://chemistry.about.com/b/2013/11/17/osmotic-pressure-and-tonicity.htm

http://differentmedicalcareers.com/hypertonic-hypotonic-isotonic-solutions/

http://www2.nl.edu/jste/osmosis.htm

http://www.slideshare.net/dewisivasamy/the-effects-of-hypotonic-hypertonic-and-isotonic

http://www.glencoe.com/sites/common_assets/science/virtual_labs/LS03/LS03.html

http://biology.unm.edu/ccouncil/Biology_124/Summaries/Membranes.html

http://www.biologycorner.com/bio1/notes_diffusion.html

http://mcatdaily.blogspot.com/2010/05/difference-between-hypertonic-hypotonic.html