THE EFFECTS OF A SERIES OF CHANGES THE
SEEDLING PHASEOLUS VULGARIS, ZEA MAYS, AND
PISUM SATIVUM GO THROUGH DURING ITS LIFE
CYCLE FROM MOVEMENT IN RESPONSE TO LIGHT,
GRAVITY, AND HORMONES
JANELLE S. ABRAHAMS
Bio 240W
Professor Dr. Michael Gannon
Section 2, Wednesday’s 1:00-2:50 pm
April 11, 2012
ABSTRACT
Plants proceed through a continuous series of change throughout their life cycle. Bean
seedlings, Phaseolus vulgaris, corn seeds, Zea Mays, and peas, Pisum sativum, were
measured and observed over a one-week period. These different plants were observed
to identify where plant growth occurs in a plant, understand gravitropism,
phototropism, and the effects of the plant growth hormone gibberellin. On day one
four bean seedlings (Phaseolus vulgaris) were measured and afterwards placed in the
greenhouse so they could continue to grow and be measured the following week. Four
corn seeds (Zea Mays) were also observed during this lab to recognize the gravity
response to their environment. After one week each of the corn kernels had roots and
stems growing out of them in different directions in response to the gravitational force,
the stems grew upwards and the roots grew downwards. The response proved that the
roots grew towards the gravitational force and thus into the soil and the stems grew up
in the direction away from gravity and thus towards the light. We then examined
another growth response to light, called phototropism. Three different treated bean
seedlings (Phaseolus vulgaris) were observed and recorded on how each differed in
growth based on their environment. Ten bean seedlings were measured from each
treatment group: dark treatment, normal light treatment, and directional light
treatment. Our last experiment observed the effects of the plant growth hormone
gibberellins. Twenty-four pea plants (Pisum sativum) were measured, 12 with the
hormone gibberellin and 12 without the hormone gibberellin. After being measured all
plants were returned to the green house and examined after one week of growing to see
how the hormone gibberellin did or did not affect the height of the plants.
INTRODUCTION
Growth is defined as an irreversible increase in volume due to a corresponding
increase in the cell size and/or number (Gannon, Michael 1-5). The bean seedlings
(Phaseolus vulgaris) grew more towards the top portion of the plant rather than the
bottom portion. The purpose of this experiment is to identify where the major growth
in the bean seedlings occurred. When examining the plant, the marks that were made
with the Sharpie marker every 5mm were smudged and spread apart more towards the
top of the plant. The marks that were made towards the roots were still 5mm apart
from each other indicating no sign of growth happening in that region. We are
experimenting the hypothesis that plants primarily in the hypocotyl region. The
expansion of the plant cells is what causes plant growth. The expansion of a plant cell
is primarily driven by the uptake of water, which enters the cytoplasm of the cell and
accumulated in its central vacuole (Sadava, Hillis, Heller & Berenbaum, 2009)
The response of a plant to gravity is called gravitropism. Roots grow towards
the gravitational force, and thus into the soil. Stems grow up in the direction away
from gravity, and thus toward the light. Four corn seeds (Zea mays) were observed
over a one-week period to recognize the response of each root and shoot growth to
gravity. Plant organs are capable of sensing various vectorial stimuli, e.g., light,
gravity, touch, and humidity. Plants reorient their growth direction to be in a suitable
position for absorption of water or nutrients, photosynthesis, and reproduction. Plants
orient their growth with the roots anchored in the soil to absorb water and minerals,
and the shoot upward to harvest light that provides energy for photosynthesis (Morita,
2010). The response of a plant organ to a directional stimulus is called tropism.
Gravity is one of the most important directional environmental cues that control
growth direction. In general, plant shoots grow upward (negative gravitropism),
whereas roots grow downward (positive gravitropism). Because the direction and the
magnitude of gravity are almost constant on the surface of the earth, gravitropism can
be regarded as a posture control, triggered by sensing the tilt of organs relative to the
direction of gravity. (Morita, 2010).
Phototropic responses involve the bending of growing stems and other plant
parts toward sources of light. Plants response to light orients the leaves in a way in
which they are able to obtain the maximum amount of sunlight. Auxin was discovered
as a result of investigations in phototropism, which is the growth of plants towards
light or away from light. Auxin is a growth hormone manufactured in the apical
meristem tissue at the tips of the shoots in the coleoptile (leaf sheath). Auxin is
synthesized in apical meristems of shoots. It causes young stems to bend toward light
when it migrates toward the darker side, where it makes young cell walls more plastic
and thereby promotes cell elongation. By interacting with other hormones, auxin can
promote an increase in girth and is involved in growth responses to gravity and fruit
ripening (Johnson & Raven, 2001). Light reduces auxin concentration in un-lighted
cells, desensitizing shoot, apical, and coleoptile tissues to auxin. This then causes
migration of auxin away from lighted tissue. This increase in auxin concentration in
un-lighted cells causes them to elongate and their shoots to bend towards light
(Gannon, 2012). The first step in a phototropic response is perceiving the light.
Photoreceptors perceive different wavelengths of light with blue and red being the
most common (Johnson & Raven, 2001). Light affects every aspect of plant
development, beginning with seed germination. A large number of blue light
responses have been documented in plants, including inhibition of the rate of
hypocotyl growth, phototropism, stomatal opening, and the induction of gene
expression (Frankhauser & Chory, 1997). The gravity signal is present continuously,
but once illuminated the combination of light and gravity defines the growth
orientation of the seedling and later of all the plant organs.
Gibberellic acid (GA) is a naturally occurring plant hormone that stimulates
and regulates plant growth (Brumbaugh, 2009). Gibberellins can have several
different effects on plants depending upon what part of the plant is involved (Gannon,
2012). Gibberellins, which are synthesized in the apical portions of stems and roots,
have important effects on stem elongation. The elongation effect is enhanced if auxin
is also present. The application of gibberellins to dwarf mutants is known to restore
the normal growth and development in many plants (Johnson & Raven, 2001). We are
experimenting the hypothesis that if gibberellic acid is a growth hormone, which
regulates plant growth, then we expect the height of the experimental group to be
higher than that of the control group at the end of our experiment. METHODS AND MATERIALS
The experiments on the effects of growth, gravitropism, phototropism and
hormonal effects were all observed over a one-week time frame. Four bean seedlings
(Phaseolus Vulgaris) were obtained from a flat provided in the laboratory. The four
different plants were all labeled, measured, recorded and then placed back in their flat
to be observed and measured the following week. The plants were primarily measured
form the hypocotyl to the epicotyl (from the soil to the end of the tip of the stem). To
obtain these measurements, we used a millimeter ruler and marked every 5
millimeters up the stem with a black sharpie marker.
Next the corn seeds (Zea Mays) were observed to see their response to their
environment. Four corn seeds were obtained and oriented in four different directions
(up, down, left, and right) in order to understand the effects of gravitropism.
TOP
corn
kernel
masking
tape
These seeds were taped into the bottom of a petri dish with a moisten paper towel
over the taped seeds. Once all the proper procedures are performed mark the top of
the petri dish and place it on its edges with the marked top facing upwards. Once
everything is done place the petri dish in a dark place and leave it to be observed the
following week.
To understand the response to light in plants (phototropism), three flats of
bean seedlings (Phaseolus Vulgaris) were provided in the laboratory. Each flat was
treated differently and have been growing for a week already. Flat #1 contained the
normal light treatment group of plants that were greenhouse grown, flat #2 contained
the dark treatment plant group which were placed in a box with no light at all, and flat
#3 contained the directional light treatment which were placed in a box in which it
received light coming in from only one direction. Ten seedlings were then observed,
measured, and recorded form each treatment group. The seedlings were measured
with a millimeter ruler from the hypocotyl to the epicotyl (from the soil to the end of
the tip of the stem).
The last experiment focused on the hormonal effect on plants due to
gibberellins. Flats of pea seedlings (Pisum sativum) were provided in the laboratory,
some contained the hormone gibberellins and some didn’t. Twelve plants with the
hormone gibberellins were measured, observed, and recorded then twelve plants
without the hormone gibberellins was observed, measured, and recorded. After all
measurements and observations are recorded leave these 24 seedlings to grow for one
week in the greenhouse. Measurements were taken with a millimeter ruler form the
hypocotyl to the epicotyl (from the soil to the end of the tip of the stem.
RESULTS
Bean Seedling (Phaseolus Vulgaris) Growth 450 400 350 300 250 Height Week #2 200 Height Week #1 150 100 50 0 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41 43 45 47 Table 1, Experiment #1 Plant Growth in bean seedlings
Twelve different groups observed 4 sets of bean seedling (Phaseolus vulgaris) and all
recorded some kind of growth over a one-week period (Table 1).
GRAVITROPISM
- There wasn’t graphed for this second experiment but 3 out f the 4 corn kernels
responded to gravity appropriately. They all had roots and shoots coming out of
them in the right direction. The Seed facing the left (2nd kernel) ended up being
dead after being left alone for a week. There are several different reasons why
this could have happened. The kernel could have been dead already or not
properly taped into the petri dish.
Phototropism in Phaseolus Vulgaris 400 350 300 250 Normal Light Treatment "Greenhouse grown" 200 Dark Light Treatment 150 100 Directional Light Treatment 50 0 1 -
2 3 4 5 6 7 8 9 10 Table 2, Experiment #3 Phototropism in the bean seedlings (Phaseolus vulgaris)
In table # 2 we can see that of the three different treated groups he tallest were the
Dark Light Treatment.
• The normal light treatment “greenhouse grown” plants were the greenest and
shortest of all the groups. The average amount of leaves was 8 and the average
length was 176.5mm.
• The Dark treatment group was the tallest of all the groups. They had white
stems, and dead yellow leaves. The average amount of leaves was 2.2 and the
average length was 319mm.
• Directional light treatment was the middle plant. All the plants were bent right
towards the light source (the hole in the box). They had light green stems and
leaves. The average amount of leaves was 2, and the average length was
213mm.
Figure 1, the effects that gibberellins has on pea plants
Hormonal Effects with
Gibberellins!
350!
300!
250!
200!
Ending Height (mm)!
150!
Beginning Height (mm)!
100!
50!
0!
1!
2!
3!
4!
5!
6!
7!
8!
9!
10!
11!
12!
Table #3, Hormonal effects with gibberellins in the pea plant (Pisum sativum)
The 12 Plants that were observed in this graph shows that with the gibberellic acid
hormone the plants tended to grow more than they normally would. The plants grew a
significant amount compared to the plants without gibberellins. Plant #6 in this data
died, this could have been caused by too much gibberellic acid or poor nutrition.
Plant Growth without Gibberellins !
160!
140!
120!
100!
80!
Ending Height (mm)!
60!
Beginning Height (mm)!
40!
20!
0!
1!
2!
3!
4!
5!
6!
7!
8!
9!
10!
11!
12!
Table #4, Growth in the pea plant (Pisum Sativum) without gibberellins
The 12 plants that were grown without the gibberellic acid grew normally but not a
significant amount like the ones with the gibberellic acid. This basically just shows
regular growth over a one-week period like the first experiment we did in (Table 1).
DISCUSSION
In plant growth and development, plants have to undergo changes during their
life cycle. The result showed in the above sections of this report shows a lot of
differences in plant growth depending on the changes they undergo. Even though all
the experiment were different, they overlapped with each other and all resulted how I
expected them to. Everything that I knew about each of the individual experiments
proved my hypotheses right. Plant growth happens primarily in the hypocotyl region
of the bean seedling (Phaseolus vulgaris) by cell expansion. The corn seeds (Zea
mays) responded to their environment appropriately, the roots and shoots grew in
response to gravity in the right direction. In this experiment one of my seeds didn’t
have an outcome so it was labeled dead. This could have been because the seed itself
was rotten or wasn’t taped down good enough in the petri dish so it was floating
around. The bean seedlings (Phaseolus vulgaris) all had different growth and leaf
counts because of the different type of treatments and the pea plants (Pisum sativum)
were elongated by the gibberellic acid hormone.
To get more accurate results, one person should of did the experiment, these
measurements are a compilation of everyone’s measurements and work put together.
I'm positive that not everyone measured each plant the same distances, some people
might have measured for the soil to the tip of the leaves and others might have
measured form the soil to the end of the stem.
An additional experiment that could be added to this lab is to observe these
plants for more than one week and see if the results are the same as the previous
week. Would the pea plants without the gibberellic acid grow to reach the lengths of
the plants with gibberellic acid? For the phototropism experiment, how would the
outcome for the directional treatment group be different if the hole was bigger or
smaller?
References
Brumbaugh, Steven G. (Spring, 2009). Laboratory 4: Pea Lab. Biology 100
Laboratory Manual. pp. 49-53.
Frankhauser, C., & Chory, J. (1997). Light control of plant development. Annual
Review of Cell Development Biology, 13, 203-229.
Gannon, M. Lab #3, Plant Development and Growth, Penn State Altoona Biology
Department. Spring Semester 2012. 1-5. Print
Harrison, B. R., Morita, M. T., Masson, P. H., & Tasaka, M. (2008). Plant
tropisms. (1st ed., pp. 21-40). Ames, Iowa: Blackwell Publishing.
Johnson, G. B., & Raven, P. H. (2001). Biology. (6th ed., pp. 807-836). McGrawHill Companies, Inc.
Lariguet, P., & Frankhauser, C. (2004). Hypocotyl growth orientation in blue light
is determined by phytochrome a inhibition of gravitropism and phototropin
promotion of photropism. The Plant Journal, 40, 826-834. doi: doi:
10.1111/j.1365-313X.2004.02256.x
Morita, M. T. (2010). Directional gravity sensing in gravitropism. The Annual
Review of Plant Biology, 61, 705-20. doi:10.1146/annurev.arplant.043008.092042
Sadava, D., Hillis, D. M., Heller, H. C., & Berenbaum, M. R. (2009). Life: The
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