MATERIALS & METHODS the continuing preparation

This week continued as a week of preparation. I know it seems like the preparation phase just keeps going on and on. But, preparation is important and proper preparation is the only way we are able to truly reach and understand our findings once we reach our ultimate goal.

In our experiment our ultimate goal is to study the effects of allelopathy on the germination of seeds of plants of the lower Sonoran Desert. But, first we must determine the conditions under which our seeds will germinate, and how long it takes.  

Materials

Petri dishes (60 pre-labeled)

Paper towels

Seeds

Method

1.     Thoroughly wash hands, this will reduce contamination

2.     Cut the paper towels to fit the bottom of the labeled Petri dish, two for each Petri dish.

3.     Put one cut paper towel into the bottom of each Petri dish.

4.     Gently count and place seeds into Petri dish (# depends on species, but should be noted)

5.     Seeds should be counted twice.

6.     Moisten seeds with 5 mL of DI water

7.     Place lids on the Petri dishes

8.     Seal lids with paraffin, careful to assure no air can get into the Petri dish as this will alter growing conditions.

9.     Repeat the above procedure; prepare five Petri dishes for each species.

10.  Store the Petri dishes in an undisturbed area of the lab; note the room temperature.

11.  Check on the progress of germination at regular intervals

Next week I hope to have some germinating seedlings!

One of the seeds we are germinating is the Carnegiea gigantean or the Giant Saguaro. These slow growing majestic plants have come to symbolize the state of Arizona, and yet in the wild germination requires conditions that are not typical for Arizona. Evidence suggests that saguaro seeds germinate after a number of years of mild and wetter than average weather conditions. These conditions are estimated to occur “only a few times a century” and may evolutionarily be why these plants grow so slowly – only 1” in 15 years - and live beyond 200 years.

Growth Chart for the Saguaro

First year – reaches height of ½ inch

Fifteenth year – reaches height of 1 inch

40-50 years – reaches height of 10 feet and begins to flower

75 to 100 years – sprouts arm buds and reaches height of 12 to 20 feet

100 to 200 years – can reach heights of 60 feet and weigh upwards of 10 tons

 

Reference:

Dimmitt, Mark, "Cactaceae". A Natural History of the Sonoran Desert.  Arizona-Sonora Desert Museum Press, Tucson.

ALLELOPATHY among species of the lower Sonoran Desert

Introduction:

Plants, like animals, are extremely complex chemical factories. These complexities are the result of evolutionary changes that promote survival. Some methods of defense include the production of chemical scents and nutrients to encourage or attract pollinators such as bees. Other methods include the production and storage of poisons which discourage consumption by herbivores/omnivores as well as parasitic attack. Plants rely on ground nutrients and photosynthesis - sun exposure – to create the fuel they need to survive and grow. As such plants must compete with other plants for sunlight, soil nutrients, and water. Since plants do not possess the ability to flee competitive adversaries they have adopted means of chemical combat. One method of reducing the competition is to simply prevent it from sprouting in the first place.  This method is known as allelopathy, a system in which one species of plant produces chemicals that effectively prevents the germination and growth of adjacent plants.

When this type of  chemical warfare is used against  plants within the same species it is known as intraspecific competition,  when it is used against plants of a different species it is known as interspecific competition.

Some of the ways plants may release allelopathic substances into their surrounding environment:

1.     Directly into the soil via their root system

2.     Chemicals may be washed off of leaves during rain

3.     Chemicals may blow into the air which are then are deposited on the soil or the surface of other plants when dew forms.

4.     Leached from living or dead shoots into surrounding soil

In today’s laboratory experience we began the initial stages of our project. Our first step was locating information on the optimal germination environment for the plants that we are going to be growing. This process involved a great deal of internet research and an attempt at contacting some of the state’s agricultural centers, including the Desert Botanical Gardens, ASU and UA Cooperative Extension.

The seeds we will be germinating include:

Ambrosia deltoidea (triangle bursage)

Cercidium microphyllum (palo verde)

Larrea tridentata (creosote bush)

Encelia farinosa (brittlebush)

Cylindropuntia acanthocarpa (buckhorn cholla)

Phacelia campanularia (desert bluebell)

Opuntia phaeacantha (prickly pear)

Eschscholzia Mexicana (golden poppy)

Sphaeralcea ambigua (desert globemallow)

Lupines arizonicus (Arizona Lupine)

Lesquerella gordonii (bladder pod)

Carnegiea gigantea (saguaro)

Today was a day of preparation. We labeled our petri dishes, prepared paper towel mediums, counted seeds and placed them in their appropriate petri dishes. No solutions were added. 

The Effects of Leaf Extract on Seed Germination By McKenna Manning & Ainsley Chapman

The seed is the flowering plant’s most basic unit of reproduction, which in response to the environmental cues it receives has evolved to assure the plants greatest chance of survival.

The project which we plan to undertake will involve five common plant species of the lower Sonoran Desert and are all located on the Phoenix College grounds, including: brittlebush, creosote bush, bursage as well as ironwood and palo verde trees.

But first, a brief review:

Anatomy of the Seed

Seeds vary according to their plant species, via natural selection and various other evolutionary forces they have evolved a number of different anatomies. As an example some are small and easily carried in the wind to either high or distant places. These seeds generally contain very little endosperm and therefore have little reserve energy to support a sprout during germination.

On the other hand, seeds that typically germinate underground tend to contain high reserves of endosperm. This is because the deeper a seed is buried the more energy is required to produce a sprout that will break the surface and begin the process of photosynthesis – thereby creating its own food.

Dormancy and Germination       

Dormancy is a state in which the seed will not germinate. This does not mean that the seed is defective or not viable; it simply means that the seed will not germinate until dormancy has been removed or alleviated. Dormancy does not have a simple temperature, time or environmental cause it is the result of, “blocks within the seed that prevent germination, as distinguished from the absence of factors required to evoke germination”(Vleeshouwers, 1995). During this time the seed metabolism is slowed and very little energy is required to stay alive.

Germination is an awaking from dormancy. It is the process, under the right conditions, when a seed begins the process of plant growth. The process of germination is typically divided into three main phases:

1.     Activation Phase

This phase begins with imbibition or the uptake of water by the seed. The most dramatic physical change in the seed is an increase in volume. The seed respiration increases and a number of enzymes are manufactured.   The enzymes will break down the endosperm into simple compounds such as sugar which will be used for growth. By the end of this phase the embryonic cells have begun to elongate and the radicle has started to lengthen.

2.     Digestion and Translocation Phase

In this phase there is a dramatic increase in the metabolic activity. Protein synthesis begins as the stored energy in the endosperm becomes metabolized.  The synthesis of enzymes to soften the cell was begins and there is a further increase in cell volume and elongation. Nutrients are transported to areas of growth, such as the embryo axis and roots.

3.     Seedling growth

This is the final stage of the germination process, when the radicle emerges from the seed coat and the embryo obtains access to water and nutrients in the environment via its’ developing root system. In this stage the primary activity is rapid cell elongation and cell division.  

Our next post will explore the factors that influence germination.

Vleeshouwers, L. M. (1995). Redefining seed dormancy: an attempt to integrate physiology and ecology. The Journal of Ecology, 83, 1031-1037. Retrieved from http://www.jstor.org.ezproxy1.lib.asu.edu/stable/2261184

A New Direction

 

       This week my internship, and therefore my blog, takes a turn in an entirely new direction. As those of you who read my blog know, I have been working with elementary age, special education students at Houston Elementary in Gilbert. However, after further consideration – and a very informative meeting with Amanda – I decided to join many of my fellow S-STEM recipients and work in the Phoenix College biology lab. Having very minimal biology this is a very exciting time for me and I can already tell that I am really going to enjoy this new adventure.

       Since all good new experiences begin with a lesson in safety it was no surprise to me that my biology lab experience began with information pertaining to safety. Clearly, any laboratory environment has the potential of being a hazardous setting. Professors and students alike are exposed to a number of potentially dangerous conditions, including: chemical, biological, radioactive and accident/injury.

       In order to maintain a safe environment all parties must abide by an enforceable code of behavior and procedure. They must respect and follow the numerous rules that have been adopted by the laboratory, whether they are the result of departmental regulations or state/federal law. Unfortunately, as a person becomes comfortable in a setting many times rules become lax and many times are forgotten.

       I found an example of an incident that occurred at Boston College in June of 2011. According to news reports a graduate level chemistry student was working alone in a lab with only a small amount of thionyl chloride. A small explosion occurred and the student received minor cuts and burns to her face and hands. Though a minor incident the student complicated matters by driving herself home before a thorough decontamination could be undertaken – as such the contamination site, which should have been contained to the lab, grew to include a car and an apartment (Wolford, 2011).

       Unfortunately, not all laboratory accidents are so easily ‘cleaned up’. In late December of 2009, a UCLA staff research assistant died after receiving second and third degree burns over much of her body in a chemical fire. Though only a mere six feet from a shower, the poorly trained researcher ran in the opposite direction. Investigation into this incident led to criminal charges being filed against UC regents and the chemistry professor who oversaw the lab (Grasgreen, 2012).

        The lab at Phoenix College is a wonderfully exciting place, I am sincerely looking forward to the time that I will spend working with the people and the equipment over the course of this semester. And, I’m glad Josh and Matt took the time to teach me about safety!

References:

Grasgreen, A. (2012). Fallout from a lab tragedy. Retrieved from
             http://www.insidehighered.com
             /news/2012/01/03/ucla-faces-criminal-charges-lab-accident

Wolford, B. (2011). Boston.com. Retrieved from

http://www.boston.com/news/education/higher/articles/2011/06