Hay Fever: Maladies, Melodies And Remedies

In addition to kicking off the barbeque, swimming and vacation seasons, spring also marks the beginning of that pesky and sometimes debilitating seasonal woe, hay fever. Much like Noel Coward’s 1924 play Hay Fever, the colloquial designation has really nothing to do with hay or fever. Clinically known as allergic rhinitis, hay fever describes the hypersensitivity to airborne allergens and the onslaught of bothersome symptoms they provoke. Approximately 20% of the world’s population suffers from seasonal or perennial hay fever. Even Paul Simon wasn’t spared from the suffocating spiral that is allergies.

 

With the blooming of spring flowers and sprouting of fresh green leaves and grasses, we are reminded that life is all around us. Quite literally, too, as windborne plant pollen is small enough to enter our eyes, nose, and mouth. Pollen, the primary cause of seasonal allergies, contains the male gametophytes of seed-bearing grasses and trees. Each pollen grain contains a generative cell, or sperm, which fertilizes the egg of the female plant, and a vegetative cell, which develops into a pollen tube and delivers the sperm to the ovule. Many trees and grasses rely on wind to spread their pollen and fertilize the female plant. So although your college roommate may have been discrete while attempting to procreate, wind-pollinated plants uphold no such personal boundaries.



Next time you smell a flower, realize you are sniffing a plant’s “naughty bits”.

So which plants are responsible for producing the powdered cheese-like substance that coats our houses, bicycles, and cars? Although thousands of plant species produce pollen that makes the Holderness family cough and gag, only a handful are responsible for their allergic wheezing and sneezing.

The exact timing of seasonal allergies can vary depending on region and climate. You can blame your early spring allergies on tree pollen, particularly that from birch trees. From March to May, many other trees including beech, ash, pine, box elder, cottonwood, oak, mulberry, elm, alder, cedar, hazel, willow, poplar, linden, olive, hornbeam, and plane contribute to early spring allergies. By June, grass pollen becomes predominant, especially timothy and ryegrass. Other grasses such as Bermuda, Johnson, Kentucky bluegrass, orchard, redtop, sweet vernal, and rye contribute to allergies. As the heat and humidity rises during July and August, your hair and electricity bill aren’t the only things that grow. Molds can thrive in grass, grains and leaves; airborne spores can cause hay fever.

The warm days and cool nights of late summer and autumn are perfect conditions for weeds, particularly ragweed, which is the primary cause of autumn-onset seasonal allergies. Ragweed can produce metric tons of pollen per square mile of plant. Other weeds that produce allergenic pollen are cocklebur, burning bush, lamb’s quarters, pigweed, plaintain, Russian thistle, sagebrush, mugwort, and sheep sorrel.

The heavy vegetation towards the end of the growing season provides a perfect breeding ground for additional outdoor mold. Mold grows in fallen autumn leaves, hay, and straw, and can be stirred up during raking or baling. In general, mold spores are considered perennial allergens because mold has the potential to grow outdoors and indoors, especially in kitchens, bathrooms, and basements throughout the entire year. However, growth conditions are optimal during different seasons, potentially resulting in a seasonal effect with mold allergies.

Even in winter, mold spores on indoor live pine trees can cause an allergic reaction. So even though the pine tree isn’t releasing pollen, it can still aggravate hay fever symptoms.

Other perennial allergens besides mold spores include dust mites, pet hair dander, and cockroach droppings. Dust mites are always present, but have been shown to increase with installation and use of central heating and insulated windows in apartment buildings. And although we may not even know cockroaches are present, the proteins in their droppings can cause hay fever. Cat dander is the most common cause of pet allergies, but thankfully The Big Bang Theory writers conveniently overlooked Sheldon’s alleged cat dander allergy so he could adopt this zazzy guy.

What is it about allergens that trigger the allergic response? Although scientists have worked to understand the molecular details of allergens and how they interact with components of our immune system, there is no clear answer as to what specifically makes something allergenic. However, within many of the most common allergens, the primary antigen has been identified. The antigen is the specific molecule that is recognized by our immune system. Antigens can be different components of a bacterial cell or viral particle; in the case of allergens, it is a protein derived from pollen, dander, mold, etc.

Pollen from birch trees is one of the largest contributors to hay fever in spring and early summer in North America The primary antigen from birch tree pollen, Betula verrucosa is called Bet v 1. The Bet v 1 antigen exists as a mixture of 14 isoforms that share ≥ 96.5% sequence identity; these isoforms possess different binding capabilities for the antibody immunoglobulin E (IgE). In fact, only 1 of the 14 isoforms, Bet v 1.0101, induces an immune response in an individual with birch tree allergy, and the two other isoforms tested, Bet v 1.0401 and Bet v 1.1001 induced no response (PMID:  20005001). Immune cells isolated from patients with no birch tree allergy did not react to any of the isoforms. The difference in the antigens is their affinity for the IgE, but precisely what makes one antigen more reactive than the other is unclear. On a basic level, the protein sequence and structure influence the binding to antibodies.


Birch pollen primary antigen Bet v 1 (wikipedia.org)

One complication with diagnosing and treating allergies is the potential for cross-reactivity between different antigens. In some parts of the world, allergic patients are double-sensitized to ragweed and mugwort, Artemisia vulgaris. The flowering season of these two plants overlaps, making it difficult to diagnose the primary sensitizer. In addition to increasing the number of allergies a patient may have, cross-reactivity also complicates prescription of the correct immunotherapy to combat the primary allergy. The primary antigen of mugwort is Art v 1 and up to 95% of people are sensitized to Art v 1. However, a minor mugwort antigen, Art v 6 shares high homology with and commonly cross-reacts with the primary ragweed antigen, Amb a 1. At least 90% of ragweed-allergen sufferers are sensitized to Amb a 1. This means that patients who are allergic to ragweed may be sensitive to mugwort and vice versa. New proteomic technologies allow for more accurate diagnoses of the primary sensitizer so that the proper immunotherapy can be prescribed. Treatment of allergies will be discussed in article 4 of this series.

With so many potential allergens bombarding us more or less year-round, it’s almost surprising that more of us don’t suffer from hay fever. As mentioned above, 1 in 5 people are afflicted and, unfortunately, that number is increasing, particularly in suburban areas of North America. Perhaps the reason allergies are not more common is because they are not hardwired into us, as is the immune response to infectious agents such as bacteria, viruses, and parasites. Hay fever is considered an atopy, a genetic predisposition to mount inappropriate immune responses to harmless environmental allergens. The immune response mounted against allergens will be described in detail in article 2 of this series.

The tendency to have seasonal allergies is hereditary, but does not follow Mendelian principles, like inheritance of eye or hair color. In addition to genes, the environment contributes to allergy susceptibility. Understanding the genetic and environmental factors involved in allergy development is complex and requires sound knowledge of the actual allergic response. A more complete discussion of genetic and environmental factors that influence allergy susceptibility will be presented in the third article of this series. We hope you’ll tune in for the remaining articles in this ongoing series.

Contributed by:  Julia van Rensburg
Follow Julia on Twitter.
 

Hirsch T, Hering M, Bürkner K, Hirsch D, Leupold W, Kerkmann ML, Kuhlisch E, & Jatzwauk L (2000). House-dust-mite allergen concentrations (Der f 1) and mold spores in apartment bedrooms before and after installation of insulated windows and central heating systems. Allergy, 55 (1), 79-83 PMID: 10696861

Leb VM, Jahn-Schmid B, Schmetterer KG, Kueng HJ, Haiderer D, Neunkirchner A, Fischer GF, Nissler K, Hartl A, Thalhamer J, Bohle B, Seed B, & Pickl WF (2008). Molecular and functional analysis of the antigen receptor of Art v 1-specific helper T lymphocytes. The Journal of allergy and clinical immunology, 121 (1), 64-71 PMID: 18037161

Jahn-Schmid B, Hauser M, Wopfner N, Briza P, Berger UE, Asero R, Ebner C, Ferreira F, & Bohle B (2012). Humoral and cellular cross-reactivity between Amb a 1, the major ragweed pollen allergen, and its mugwort homolog Art v 6. Journal of immunology (Baltimore, Md. : 1950), 188 (3), 1559-67 PMID: 22205029

Wopfner N, Bauer R, Thalhamer J, Ferreira F, & Chapman M (2008). Immunologic analysis of monoclonal and immunoglobulin E antibody epitopes on natural and recombinant Amb a 1. Clinical and experimental allergy : journal of the British Society for Allergy and Clinical Immunology, 38 (1), 219-26 PMID: 18028463

Asero R, Bellotto E, Ghiani A, Aina R, Villalta D, & Citterio S (2014). Concomitant sensitization to ragweed and mugwort pollen: who is who in clinical allergy? Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology, 113 (3), 307-13 PMID: 25053399

O Christmas Tree: It’s Not Easy Being Green

Evergreens are a remarkable mainstay in the evolution of plants. Evidence suggests that they have existed more or less in their present form for the past 300 million years. In other words, the evergreens are so resilient and exquisitely adapted to their environment that nature has not tweaked with their genetic recipe since the Permian. The evergreens can survive just about anything nature can throw at them, except humans. Nearly 40 million of these stoic conifers are chopped down each Christmas season in North America alone.

"Christmas Tree" farms cultivate a variety of evergreens that will grace one of 40 million homes each season. This makes it a lot easier than hiking into the forest to cut one down yourself.

Humans have long been fascinated by the evergreens because these trees and shrubs do not lose their leaves (needles) in autumn like the broadleaf trees. Seemingly in defiance to the harsh winter, the aptly named evergreens stay full and green all year long. Impressed with this act of endurance, early humans thought that evergreens must hold special powers. The ancient Pagans would place evergreen branches over their doors and windows to ward off evil spirits, especially during the winter solstice when the days were at their shortest and the nights at their coldest. Evergreens served as a reminder that the days would lengthen and the crops would grow once again in the spring.

A decorated evergreen is now synonymous with “Christmas Tree”, but this ritual has its “roots” in Paganism. Interestingly, it has even been argued that this passage from the Bible forbids emulating this Pagan practice.

So how do evergreens stay green year round? In winter, shorter days mean less sunlight. As sunlight is required for photosynthesis, plants face a dramatic reduction in energy during winter. To cope with this, broadleaf plants stop making chlorophyll, the molecule that drives photosynthesis and reflects green light. Consequently, the leaves change color and eventually fall off as the tree goes dormant.

By way of comparison, evergreen “leaves” do not have a lot of surface area; they are more resistant to lower temperatures and decreased moisture. Chlorophyll in these needle-like leaves is retained and photosynthesis can still generate energy from light, albeit at a much slower rate than spring or summer.

In addition to keeping chlorophyll, retaining moisture is equally important:  trees cannot extract water from frozen ground, and occasional sunlight in the winter can draw out precious moisture. Evergreen needles have a thick coating of wax and a slender shape, characteristics that help them hold water in and prevent evaporation, respectively.

A recent study has shown that the conifer’s ability to survive arid times involves the coordinated evolution of tissues regulating water supply (xylem) and water loss (stomatal pores) in the needle leaves. A plant hormone called abscisic acid helps keep the leaf’s pores sealed when water isn’t available. Another mechanism allows leaves to dehydrate and resist damage via a water transport system.

Close up image of pine needle – the small pores are stomata, which open and close to regulate gas exchange. When open, water vapor can escape.

Conifers have thousands of needle leaves, which help maximize energy production while not losing water to dehydration. Of course, evergreen needles do not last forever. They do need to be replaced, but conifers do this intermittently and a green appearance is always observed.

Ever since ancient times, the evergreens have been admired for their stamina and hardiness through the winter. They are a source of inspiration reminding us that better times are ahead. In this light, the ritual chopping down of the tree for decoration seems a most bizarre way to honor the mighty evergreen. Consider, instead, a Festivus Pole.
 

Contributed by:  Bill Sullivan

Follow Bill on Twitter.

Brodribb TJ, McAdam SA, Jordan GJ, & Martins SC (2014). Conifer species adapt to low-rainfall climates by following one of two divergent pathways. Proceedings of the National Academy of Sciences of the United States of America, 111 (40), 14489-93 PMID: 25246559

I Am Groot! Plants Are More “Alive” Than We Think

So who saw Guardians of the Galaxy this summer? Awesome, wasn’t it? How could a movie with a talking raccoon and a 1970s-based soundtrack go wrong? Oh, and then there’s Groot, the beloved walking, talking tree-like creature who sprouted the catch phrase, “I AM GROOT!” Until Groot, the only sentient plants children probably knew of were the Evil Trees hurling apples at Dorothy in The Wizard of Oz. But Groot was a “Giving Tree” incarnate.    



Groot shatters the evil living plant stereotype and saves the day in Guardians of the Galaxy.

 

Groot was so endearing, he has given my kids a new reason not to eat their veggies – they don’t like the idea of slaughtering plants. When I reminded the kids that plants are only sentient in the movies, they gave me the look of skepticism. I know it well…I taught it to them. This inspired me to leaf through some botany literature. Much to my surprise, my kids might have a point! Plants are more “alive” than we ever imagined.

Exhibit A.  Plants know when they are being eaten alive! And they fight back…

There is a plant that scientists typically use as a model to study in the lab called Arabidopsis (thale cress, similar to broccoli but tastes even worse). Researchers recently discovered that when they expose these plants to vibrations that mimic those produced by a hungry caterpillar, the plants increase production of glucosinolate and anthocyanin defenses. These are mustard oils that don’t sit well with caterpillars. In other words, the plants can tell when they are being chewed on and release oils to deter the predator.

Another sophisticated defense system used by plants comes from studies on tobacco. When caterpillars attack, these tobacco plants produce “green leaf volatiles”, compounds that act as a distress call by attracting insects that devour caterpillars!

The Hungry Caterpillar: Adorable children's tale or a horror story of gruesome predation?

 

Exhibit B. Plants have a memory and can be trained.

Everyone is familiar with the story of Pavlov’s dog, the famous experiment that demonstrated classical conditioning. Dogs salivate when presented with meat. If you ring a bell before presenting the meat, the dogs become conditioned to salivate at just the sound of a bell. Plants do a similar thing when exposed to light. Researchers have shown that when a plant is exposed to a certain wavelength of light, and then infected with a plant pathogen, the plant “learns” to build up resistance to that pathogen when it “sees” that particular wavelength of light once again. Plants that were infected and then exposed to the light developed no protective response. Plants must possess some sort of biochemical nervous system and memory in order to execute this kind of behavior.

Plants don’t have a brain, but they do behave as if they can think.

 

Exhibit C. Plants protect their young.

Seeds are the equivalent of a plant’s babies and plants have evolved a variety of fascinating ways to take care of their young. Consider serotinous plants, which keep some of their seeds inside the plant body instead of releasing them into the environment where they can be eaten or destroyed by weather. These plants can hold onto their seeds and release them when the time is most favorable for them to survive.

In the 1986 film, “Little Shop of Horrors”, the carnivorous plant Audrey II demonstrated a terrifying new way plants could protect their kin.

 

In another striking example, scientists studying a plant called sea rocket (Cakile edentula) noticed that when grown in a pot with a different member of its species, its roots grew wildly so to soak up more water and nutrients from its competitor. However, if the sea rocket was put into the same pot as its offspring, this competition did not take place!

Still not convinced that plants are more alive than we give them credit for? Check out this video by Michael Pollan.
 

 

While the evidence above isn’t sufficient to conclude that plants on Earth are like Groot, it is clear they are capable of some level of feeling and response. But don’t tell your vegetarian friends…what else would they eat?

Contributed by:  Bill Sullivan

Follow Bill on Twitter.

 

 

Appel HM, & Cocroft RB (2014). Plants respond to leaf vibrations caused by insect herbivore chewing. Oecologia, 175 (4), 1257-66 PMID: 24985883

Allmann, S., & Baldwin, I. (2010). Insects Betray Themselves in Nature to Predators by Rapid Isomerization of Green Leaf Volatiles Science, 329 (5995), 1075-1078 DOI: 10.1126/science.1191634

Karpiński S, & Szechyńska-Hebda M (2010). Secret life of plants: from memory to intelligence. Plant signaling & behavior, 5 (11), 1391-4 PMID: 21051941

Dudley SA, & File AL (2007). Kin recognition in an annual plant. Biology letters, 3 (4), 435-8 PMID: 17567552