Exploring Plant Hormones
In class, we explored a few analyses that have led to our current understanding of the roles of
hormones in various plant processes. This lab is your opportunity to carry out your own experiments! You will
be studying a dwarf plant variety whose short stature is hypothesized to be due to altered hormone signaling.
The first part of your analysis, which will occur in the same lab period as your Termite Lab Report Peer
Review, will involve observing the plants, developing hypotheses, and setting up your experiment. In Part II of
the lab, you’ll develop predictions based on your hypotheses, and collect preliminary data. The following week,
you’ll collect and begin to analyze your data. As a post-lab assignment, you will finish your data analysis and
create a document in which you present the results of your experiments, and draw conclusions.
IMPORTANT: In addition to this handout, please review your notes from class regarding the basic features of
hormones and plant hormone analyses we discussed.
OUTLINE OF ACTIVITIES
• Part I: Make Observations, Develop Hypotheses, & Set Up Experiment
• Part II: Make Predictions & Collect Preliminary Data
• Part III: Collect Data & Start Data Analysis
LEARNING OBJECTIVES
• Practice gathering observations to aid in hypothesis development.
• Apply your understanding of plant hormones to develop informed hypotheses and predictions.
• Further develop your data analysis and presentation skills.
• Be able to draw appropriate conclusions based on your data.
INTRODUCTION
Brassica Background
Brassica is a group of closely related flowering plant species, many of which are of agricultural and
economic importance. These species include crop plants commonly known as cruciferous vegetables (e.g.
broccoli, Brussel sprouts, cauliflower), as well as oil plants used for both consumption, and biofuel (e.g.
canola). Due to their importance, significant effort has been put into better understanding the growth,
development, and disease susceptibilities of Brassica. Since many species have long generation times (time
from planting to seed production), scientists have worked to generate plant varieties that germinate and
produce seed more rapidly. Through artificial selection, a process by which humans selectively breed
individuals that possess desired traits, researchers have generated Brassica plants with very short generation
times. These plants flower about two weeks post-planting, and seeds can be harvested in about a month.
Unselected Brassica species can take up to six months to produce seeds, so these faster-growing varieties
represent valuable experimental tools that allow scientists to carry out analyses much more quickly. In the
process of selecting plants with shorter growing cycles, many other interesting traits were observed and
various varieties of rapid-growing Brassica now exist. Scientists are still working to unravel the differences in
internal processes that lead to these variety-specific traits.
For your analyses, you will be studying a dwarf variety of rapid-growing Brassica, which, as its name
suggests, is much shorter than typical Brassica plants. Plants that possess the trait most commonly observed
in a group, in this case “tallness,” are referred to as wild-type. As you know, hormone signaling plays an
essential role in virtually all plant process, including growth! Therefore, it has been hypothesized that altered
1
hormone signaling contributes to the differences observed between wild-type and dwarf plants. Previous
studies have identified a candidate hormone, and few analyses in unrelated plant species indicate that the
hormone acts to promote plant growth. Other reports, however, suggest it acts as a growth inhibitor.
Experiment Overview
Your goal is to carry out an analysis that addresses two questions: 1) does the hormone act as a growth
promoter or growth inhibitor in rapid-growing Brassica, and 2) assuming that altered signaling of this hormone
contributes to the short stature of the dwarf plants, how is the signaling pathway altered. For your analyses,
you will be provided with wild-type seeds, dwarf variety seeds, and a solution of the hormone dissolved in
water. As you’ve seen in the analyses we discussed in class, one of the great things about studying plant
hormones is that, very often, you can gain a better understanding of the effects of the hormone by simply
applying it to the plant! The hormone is able to diffuse into the plant and can interact with receptors on cells
that are capable of binding the hormone. Of course, if there are no cells in the plant that possess receptors for
the hormone, the hormone won’t have any effects. After your plants have germinated (sprouted) you will apply
the hormone solution and allow the plants to grow further, and then collect measurements to assess your
hypotheses.
Although we covered the basic structure of flowering plants, there are a few more details that you may find
helpful for your analysis. The diagram and descriptions below illustrate these additional features.
•
•
•
•
apex: tip of the main stem; considered the top of a plant
nodes: points along the stem where leaves are attached
internodes: portion of the stem between nodes
branch: an extension that grows out of the stem
2
Part I: Observations, Hypotheses, & Planting
For your analysis, you will work in groups of two. Both partners should record their OWN observations and
hypotheses. You will need these for the next part of this lab.
Lab Activities Outline
I. Quiz
To prepare for the quiz, read this handout carefully AND review your notes from our discussions in lecture
on the basic features of hormones and the role of hormones in plant processes.
II. Lab Discussion: plant hormones lab overview
III. Make Observations and Develop Hypotheses
Observe the wild-type and dwarf plants provided for you. Focus on identifying common and unique
features of the two plant types, and record your observations. Using your observations and the information
provided in this handout, develop TWO hypotheses that address the questions of whether the hormone
promotes or inhibits growth in Brassica, and in what way the signaling pathway could be altered. Each
hypothesis must address BOTH questions. (Think about why this is important!) You should also identify at
least two features that you could measure to collect data for your analysis.
IV. Lab Discussion: hypotheses, measurements, & planting instructions
V. Experiment Set-Up: planting
Follow the instructions given by your lab TA to plant your wild-type and dwarf seeds. Your plants will be
taken care of for you over Spring Break, and undergo one round of hormone treatment. When you return,
you will collect preliminary data, and treat the plants with the hormone a second time.
IMPORTANT: You must bring your Plant Hormones Observations and Hypotheses sheet to the next lab
period. Don’t lose it over spring break!!
3
Part II: Predictions & Preliminary Data
This week you will make predictions for each of the hypotheses, gather preliminary data, and apply a second
hormone treatment to your plants. You will start your Plant Hormones Preliminary Data Analysis assignment
and finish it on your own before next lab period. Therefore, each person should be sure to record their OWN
preliminary results. IMPORTANT: Remember to bring the Observations & Hypotheses sheet you completed in
the first part of this lab back this week!
Lab Activities Outline
I. Quiz
To prepare for the quiz, review this handout carefully AND your notes from your Plant Hormones Lab Part I
discussions, including your Observations & Hypotheses sheet!
II. Lab Discussion: hypotheses (review)
III. Prediction Development
Work with your lab partner to develop predictions that would support each of your hypotheses. Once you
have completed your predictions, check in with your lab TA and then go get your plants.
IV. Collect Preliminary Data and Perform Second Hormone Treatment
At this point, you plants are too small to be able to collect accurate quantitative data, and you cannot
directly assess features that require uprooting and/or killing the plant. Instead, collect qualitative (i.e.
observational) data on the three features you are using to evaluate your hypotheses. Record any
additional observations that are relevant to your analyses. Follow your lab TA’s instructions to perform a
second hormone treatment.
IMPORTANT: Your completed Plant Hormones Preliminary Data Analysis assignment is due next week at the
beginning of your lab period.
4
Part III: Data Collection & Analysis
Your goal this week is to collect data and begin to analyze it. You will complete the analysis and draw
conclusions on your own, and then turn in your completed Plant Hormones Data Analysis assignment next
week at the beginning of lab.
Lab Activities Outline
I. Quiz
This quiz will focus on assessing your understanding of data analysis and presentation. To prepare for the
quiz, review this handout carefully AND review what you learned in the Termites Trail-Following Lab
activities and Excel Workshop regarding data analysis and presentation.
II. Lab Discussion: preliminary data analysis & data analysis expectations
III. Collect Data and Start Your Data Analysis
Collect measurements on the three features you chose to evaluate your hypotheses. Use Excel to
calculate means and standard deviations, and to perform the appropriate t-tests. If there is time, you may
choose to make the appropriate graphs and/or tables. Be sure to e-mail any files you generate to yourself
(or bring a flash drive and copy the files). You must write your conclusions INDIVIDUALLY, so be sure that
BOTH lab partners have copies of the files before you leave lab!!
IMPORTANT: Your completed Plant Hormones Data Analysis assignment is due next week at the beginning of
next lab period.
5