Saturday, February 27, 2016

Best Biochemist: ABA

Growth hormones are critical to plant development, much in the same way they are for animals. Previously, I wrote about ethylene, the ripening hormone. Today, we'll look at abscisic acid (ABA), an important growth and stress hormone.

Biochemically, ABA is a 15 carbon derivative of zeaxanthin, a carotenoid, with the following chemical structure.

public domain
ABA was discovered over 50 years ago in abscising leaves. Abscission is the process by which plants detach leaves or ripened fruit. Thus the name abscisic acid. Though we now know that ABA does not play a role in abscission itself but rather cessation of growth that precedes the actual detachment process. In the 50 years since discovery, ABA has been shown to play a role in a multitude of pathways. These include: seed dormancy, embryo development, germination, cell division, flower induction, stress responses (drought, salt, cold, UV, pathogens), and stomatal closure. Let's start at the beginning of the plant's life cycle and take a look at the roles ABA plays in these processes.

Seeds in the ground remain dormant, in a state of suspended growth. The production of ABA is high during late embryo maturation which drives dormancy. Dormancy must be broken for the seed to germinate. When it is time for the seed to germinate, gibberellic acid and ethylene production results in a cascade that mutes the detection of ABA breaking dormancy. Germination then occurs and the plant grows.

As plants grow they can encounter many abiotic stressors. Personally, I research abiotic stress biology so I find the stress responsive role ABA plays to be one of the most interesting. Plant perception of environmental conditions such as, high salt, low water, cold, and wounding, all involve ABA. These stressors increase ABA levels which in turn activates stress responsive genes. The main function of ABA in all of these stresses seems to be controlling the water level within the plant in a number of ways, including gene activation, increasing water uptake in the roots, and closing the stomata.
Stomata Personal Image
Stomata are pores on the leaf that allow gas exchange, including water vapor. To close the stomata, ABA binds to receptors on the guard cells that control opening and closing of the stomata. These receptors allow the flow of ions such that the guard cells lose water and close the pores. This prevents water from leaving the leaf!

Flowering is an important stage in plant development, resulting in the production of seeds and the next generation of the species. As with all developmental phases, several hormones play important roles. The ratio of each and amount of cross-talk between the various hormone pathways results in the change of developmental stage.  Floral development requires an increase in ABA and decrease in ethylene to the proper ratio.

As the plants age, they will inevitably undergo senescence and die. The biosynthesis of ABA, along with a suite of other hormones, is increased while cytokinin is decreased. ABA works in a positive feedback manner. As ABA levels increase, water and minerals are pushed out of the leaf and into the stem. This results in dehydration of the leaf and further production of ABA. This sets up the leaf for abscission which is controlled by ethylene.

As we can see, ABA is an incredibly important hormone. It plays a role in almost every developmental stage a plant undergoes from germination to senescence. How exactly the plant knows when ABA means flowering, dehydration stress, or senescence is still a mystery. It is probably in part to genetic control, age of the plant, and coordination with other hormone levels. Plant growth and development is just as complicated as it is in animals.

Beaudoin, N., et al., 2000. Interactions between Abscisic Acid and Ethylene Signaling Cascades. The Plant Cell 12:7 1103-1115

Daszkowska-Golec, A., 2013. Open or Close the Gate - Stomata Action Under the Control of Phytohormones in Drought Stress Condition. Frontiers in Plant Science 4 138 doi 10.3389/fpls.2013.00138

Finkelstein, R. 2013. Abscisic Acid Synthesis and Response. Arabidopsis Book. 2013; 11: e0166. Published online 2013 Nov 1. doi:  10.1199/tab.0166

Lee, I., et al, 2011. Age-dependent action of an ABA-inducible receptor kinase, RPK1, as a positive regulator of senescence in Arabidopsis leaves. Plant Cell Physiology 52(4) 651-662

Tuteja, N. Abscisic Acid and Abiotic Stress Signaling. Plant Signaling & Behavior 2(3) 135-138 

Wilmowicz, E., 2008. Ethylene and ABA interactions in the regulation of flower induction in Pharbitis nil. Journal of Plant Physiology 165 (18) 1917-1928

Sunday, February 21, 2016

Minecraft Character Ornaments

This week my laptop got stolen and I lost my science post I was working on, which was very disheartening. So I'm going to take a short break from my normal science-y posts and bring you this post about Boo's Minecraft birthday party from a few months back!

One of the activities I came up with was making a Minecraft ornament. I had found some 1.5 inch paper mache block ornaments from Micheal's at 1/2 off so they were < $1 each!

To simplify things during the party, I created 4 color packs with 3 face options they could copy onto their blocks. Since the ornaments had 4 sides, the kids would rotate around the packs picking a face and gluing the correct color onto the ornament base. Then they would leave with an ornament full of their favorite Minecraft faces!

The packs were:
Green - Creeper, Zombie, Slime
Black - Enderman, Spider, Ender Dragon
Tan - Steve, Alex, Sheep
Gray - Skeleton, Wolf, Moo-shroom
After the party, for fun I also created a squid and ocelot pattern.

After I designed the patterns, I cut 1/2 inch squares out of all of the colors I needed from scrapbook paper. I had a dark green, light green, black, purple, pink, red, gray, tan, brown, white, orange, yellow, and blue.

A few characters required special pieces. For example, the creepers mouth, slime mouth, zombie eyes, and squid pupils. I cut all of those out by hand.

 The paper squares were put into plastic cups as needed for each station. Once the kids got started, they really enjoyed this activity! I gave each boy a glue stick for them to glue each piece. Some decided to drag the paper square over the glue then put it on, others spread glue all over the ornament and then stuck the paper onto the glue.  

On the bottom, I added the logo from Boo's party with the date so they would know where they made it. On the top, I had them put their names so while the glue was drying and we were doing our scavenger hunt we would know which ornament went in which goodie bag!

This project was a lot of fun. Since I have a big paper cutter, it was easy to set up as well. Finished ornaments were adorable and the boys raved about them. You can see some of the resulting faces below!

 This Friday we'll be back to science, thanks for indulging me on my Mom post!

Sunday, February 14, 2016

A Valentine's Day Species Spotlight!

Roses are Red
Violets are Blue
Sugar is Sweet
And so are you! 

A classic oldie, but goodie poem that makes the rounds on Valentine's Day. For this very special Species Spotlight we are going to take a quick look at the 3 plants that star in this classic nursery rhyme.

Personal Image

are not always red! I briefly talked about roses at July 4 as they are the national flower of the USA. The Rosaceae family contains over 2500 species, including some agriculturally important ones: apples, strawberries, raspberries, pears, plums, and more. The poem above is, of course, talking about flowers from the genus Rosa. There are over 100 species in this genus.

And while "Every rose has its thorns" is a popular lyric, rose thorns are not true botanical thorns but rather prickles. Thorns are a modified branch. Prickles are modified from the epidermis tissue on the stem. Though I suppose "every rose has its prickles" does not sound as sharp ;)

Personal Images

are not usually blue! The Violaceae family contains around 800 species, the commonly called violet flowers are within the genus Viola. Viola sororia or the common blue violet, is quite popular representing Illinois, Rhode Island, New Jersey, and Wisconsin as the state flower. Violets have 5 petals and 5 sepals (the green part behind the petals) that are arranged asymmetrically. Their leaves and petals can be heart shaped which makes them a nice match for Valentine's Day.

The bright coloration of violets is to attract pollinators, such as bees. The bees will have to burrow deep into the flower to get to the nectar, ensuring pollen will be transferred to the bee to be taken to another violet. Violets have fascinating seed pods that allow the seeds to become flying projectiles. Drying out of the seed pod increases the pressure and eventually POP! Seeds go flying. This allows the violet to spread rapidly. This rapid spreading, and hardiness of the seeds, contributes to the ability of violets to quickly spread over an area. Watch the video below to see the amazing exploding violet seed:

Another incredible way that violets can spread seed is via ants. Violet seeds are covered in a rich oily covering called an elaiosome. This sugary oil attracts the ants which drag the seed back to their nest. After the elaiosome is consumed, the exposed seed can now germinate in ant fertilized (read full of ant poop) soil. This mutulistic relationship has a very long fancy name: myrmecochory and it is found in 1000s of other flowering species.

Sugar Cane

is indeed sweet, after processing. Sugar cane is a grass from the genus Saccharum and it is in the same family as other important crops such as wheat and rice. Sugar cane is though to have been introduced to America by Christopher Columbus. The tall, thick stems of sugar cane have a sucrose filled sap. This sap is removed and then boiled and crystallized to form sugar! Since the stems, and not the fruit, are the agriculturally important part, they can be harvested repeatedly without having to replant from seed.

As a fan of photosynthesis, in my opinion one of the coolest things about sugarcane is how they do photosynthesis. They do what is known as C4 carbon fixation. Light capture happens the same way in C3 ("normal" photosynthesis) and C4 plants, it is the Calvin Cycle that is different. One of the downfalls to photosynthesis is photorespiration, when RuBisCo utilizes oxygen instead of carbon dioxide. To get around this, C4 plants have a special modification, called kranz anatomy.

Inside the leaf, there are "wreath" shaped bundles of bundle sheath cells surrounded by mesopyll. Only the bundle sheath cells have RuBisCo and all of the carbon dioxide produced by the light-reactions is passed to these bundle sheath cells from the mesophyll cells. The movement of carbon dioxide between the cells is facilitated by a 4 carbon compound, hence the name C4 carbon fixation. This is advantageous as it concentrates the carbon dioxide around RuBisCo and drastically reduces the amount of photorespiration. Reducing photorespiration means that more energy goes into sugar production. Thus C4 carbon fixation is the true reason sugar is so sweet.

And so are You

Happy Valentine's Day to all of my readers!


Friday, February 5, 2016

Species Spotlight: Garlic Mustard

One of my favorite plants is Garlic mustard, or as it is known in science Alliaria petiolata. It was the first plant I spent a significant amount of time researching, forming the backbone of my honors undergrad thesis. This is why, despite its reputation, I will always have a fond spot for this weed. 

2nd year Garlic Mustard - Personal image
Garlic mustard is a biennial mustard native to Europe. In 1868, the first documented garlic mustard arrived in New York and thus begins an alien invasion. Genetics has suggested that garlic mustard was brought over multiple times, from multiple regions in Europe which has led to a high genetic diversity in North America.

As a biennial, garlic mustard requires 2 years to flower and produce seed. The first year is spent as a rosette, a small bundle of leaves.In the second year, the inflorescence (flowering stem) shoots up. Each plant can produce thousands of seeds. Each seed can live up to 5 years in the soil before germinating. The longevity of the seed bank is one of the reasons garlic mustard is difficult to control. It would take over 5 years of gathering every single one of those thousands and thousands of  plants that germinated from the seed bank to successfully clear an invaded area. 

Garlic Mustard with siliques (seed pods) - Personal image
Garlic mustard is able to wage chemical warfare upon other seedlings and mycorrhizal fungi. Mycorrhizal fungi is symbiotic with the roots of many plant species, they provide nutrients that the plants are unable to synthesize and vice versa. When garlic mustard invades a region the mycorrhizal fungi is greatly reduced, resulting in the death of the native plants that rely on it. For garlic mustard this is perfect, more real estate! For the invaded forest this decreases the species diversity.

As the name suggests, garlic mustard tastes like a mix of garlic and mustard. This particular  combination is disliked by the common large herbivore in North America: deer. Deer ignore garlic mustard, but eat the native plants. Clearing even more room for garlic mustard to invade!

Me taking field notes in a field of garlic mustard (white flowers)
Lots of factors have played into garlic mustard's takeover of North America, yet it is not preset across the entire continent. One of the factors that has limited garlic mustard spread is it requires a lengthy cold period for germination. The mimicking of a natural cold period in the lab is called startification. During startification, the seeds are kept moist and cold, mimicking the conditions of cold/frozen ground. This softens the seed coat so that when temperatures increase in the spring the seed germinates. Garlic mustard requires 12 - 16 weeks of startification for germination. This is what keeps garlic mustard contained to Canada and the northern US. Beyond this, there are not many other road blocks to stop this alien invasion.

The most effective control method is pulling the plants before they can make seeds. For small invasions this works well. However, garlic mustard's fast spreading rate (some predictions say >3000 miles/year) and the fact that seeds can persist for 5 years makes manual removal a difficult task for larger invasion areas. Herbicides are effective but can cause further damage to native flora. 

If you find some garlic mustard, pull it before it makes seeds. If you are feeling adventurous, you can use the plants for a number of recipes! My undergrad advisor had a soup recipe that was pretty tasty! A number of which have been put together in the Mid-Atlantic Invasive Plant Council Garlic Mustard recipe file. I haven't had the chance to try these recipe but that ricotta dip will be a must try this spring! Garlic mustard should be coming up in March/April so let me know which of the MAIPC recipes you try!

Delaware DNR made an info video about garlic mustard which I will leave you with:

  • Baskin, J. M., C. C. Baskin. 1992. Seed germination biology of the weedy biennial Alliaria petiolata. Natural Areas Journal 12(4):191-197.
  • Durka, W., Bossdorf, O., Prati, D., & Auge, H. (2005). Molecular evidence for multiple introductions of garlic mustard (Alliaria petiolata, Brassicaceae) to North America. Molecular ecology, 14(6), 1697-1706. Research Gate PDF
  •  Meekins, J. F., and B. C. McCarthy. 1999. Competitive ability of Alliara petiolata (garlic mustard, Brassicaceae), an invasive nonindigenous forest herb. International Journal of Plant Sciences 160(4):741-752.
  • Nuzzo, V. 1991. Distribution and spread of the invasive biennial Alliaria petiolata (garlic mustard) in North America. P. 137-145. In McKnight, Bill N. ed. Biological Pollution: The Control and Impact of Invasive Exotic Species. Indiana Academy of Sciences: Indiana, USA. 
  • Rodgers, V. L., Stinson, K. A., & Finzi, A. C. (2008). Ready or not, garlic mustard is moving in: Alliaria petiolata as a member of eastern North American forests. Bioscience, 58(5), 426-436. 
  • Wolfe, B. E., Rodgers, V. L., Stinson, K. A., & Pringle, A. (2008). The invasive plant Alliaria petiolata (garlic mustard) inhibits ectomycorrhizal fungi in its introduced range. Journal of Ecology, 96(4), 777-783. PDF