Increased Carotenoid and
Beta-Carotene Levels in
Phaseolus lunatus (Lima Beans)
Grown under Ultraviolet Light
Stephanie Brown, Megan Wendt,
and Nick Smith
Abstract:ÊÊ
Our goal in stream one was to
determine the effects of excess ultraviolet (UV) light on lima bean plants,
their pigment, carbohydrate, and protein production.Ê We began by growing three sets of bean
plants, one grown without light, one with light, and one with high levels of
UV-B light.Ê We first tested the plants
for differences in carbohydrates using Benedictâs test for reducing sugars,
Barfoedâs test for monosaccharides, and an Iodine test for starch.Ê Quantitatively measuring precipitate mass
showed that plants grown in the absence of light contained the lowest levels of
carbohydrates, the plants grown under normal light contained the most, and the
UV-B exposed plants fell in between as we predicted.Ê Next we tested the plants for varying pigment
levels.Ê Using paper chromatography and a
spectrophotometer to determine the action spectrum for each set of plants, we
determined that the plants with the most carotenoids, seems to be those
subjected to the UV-B treatment, supporting our original hypothesis.Ê The amount of carotenoids in the normal
plants was slightly lower, and plants grown with no light contained no
pigment.Ê Finally, we measured total
protein concentration using a
Figure:
Figure 1: This picture shows the effects of growing the same lima bean
plants is three different light environments. On the far left the plants shown
were grown under normal white light. In the middle the lima beans were grown
under UV-B lights. On the right the lima beans were grown in no light. The UV-B
lights caused the lima beans to produce plants that have high levels of
carotene pigment, which caused the plants to be dark orange. The lima bean
plants grown in the dark have no
pigment, which is why the plants are white.
Discussion:ÊÊ
The hypotheses we made for our
project were: Lima bean plants grown under normal light will produce greater
amounts of carbohydrates, chlorophyll pigments, and protein. Lima bean plants
grown under UV light will produce lesser amounts of carbohydrates and proteins,
but greater amount of carotenoids and protective pigments such as
β-carotene. Lima bean plants grown in no light will produce the smallest
amounts of carbohydrates, pigments, and protein.Ê We made these predictions thinking that
plants grown under normal conditions would be the healthiest and therefore the
best at producing chlorophyll, which powers photosynthesis, which creates
energy for protein synthesis.Ê The UV
group however should, according to our research, produce more carotenoids and
β-carotene to protect itself from the destructive wavelength, while plants
grown in the dark would have little use for chlorophyll and thus have less
pigment.Ê
To test
these hypotheses we devised a project that performs tests involving
carbohydrates, pigments, and protein.Ê
With increasing amounts of UV-B light coming through the ozone, it is
apparent that plants will begin to strengthen themselves against these harmful
rays. (Davidson et al. 2002).Ê After
performing our experiments we were able to conclude that plants expose to ultraviolet
light will produce more carotenoids and carotene pigments for protection. The
question that we were seeking to answer was: Does excess UV light have an
affect on the production of carbohydrates, pigments and protein in lima bean
plants? We devised a project that would answer just that question.
The
carbohydrate tests we performed were Benedictâs test, Barfoedâs test, and
iodine test (Krha et al. 2004). We predicted that precipitate would form in
Benedictâs and Barfoedâs tests indicating the presence of reducing sugars and
monosaccharides that are reducing sugars.Ê
We also predicted that we would have the greatest mass of precipitate
from the plants grown in normal light, the second most from UV light, and
lowest for the plants grown in the dark.Ê
We predicted that the absorption for the iodine test would be greatest
for the normal light control group, the UV light would have second highest, and
no light control group would have the lowest absorption. After performing each
test our predictions were accurate only for Benedictâs test.Ê Benedictâs test did produce a copper
precipitate (Figure 1).Ê After filtering
and drying the precipitate, we weighed and found the mass of the precipitate to
be the highest for the plants grown under normal light with 0.181 g, the second
highest for the plants grown under UV light with 0.136 g, and the lowest for
the plants grown with no light 0.081 g (Figure 2, Table 2).Ê We suggest that the sugar content is
proportional to the amount of precipitate from Benedictâs test, normal light
being the greatest and the absence of light being the lowest with UV light in
the middle.Ê Therefore, sugar production
is greater in normal light (Krha et al., 2004).
Ê Because Barfoedâs test produced a white
precipitate that was not expected, it provided no conclusive evidence for us
(Figure 3).Ê The sugars tested were not
primarily monosaccharides (Krha et al. 2004).Ê
The precipitate that did form we weighed and found UV light to weigh the
most at 0.175g, dark next at 0.157g, and normal light last at 0.116g (Figure 4,
Table 2).Ê Because this precipitate was
an unknown substance, we do not know what caused the reaction or what
precipitate formed and cannot use this information to support our claims, only
to refute our predictions of Barfoedâs test.Ê
The iodine
test indicated that all of the plants contained starch, as a color change
indicates the presence of coiled polysaccharides (Figure 5).Ê Our results from running our iodine test
solutions through the spectrophotometer were not as expected.Ê Plants grown under UV light had greatest
transmittance and an intermediate absorbance.Ê
Plants grown in normal light had the second highest transmittance and
the lowest absorbance, and plants grown with no light had the lowest
transmittance and highest absorbance.Ê
This indicates that the solution of the plants grown in the dark had the
greatest absorption difference, absorbing the most light, and the darkest color
change due to the iodine test: therefore, the most starch.Ê Normal light followed.Ê Ultraviolet light contained the least
starch.Ê This was not what we expected to
find.Ê Either our predictions were
ill-founded due to an error in reasoning or our tests were not accurate due to
color change and differing absorption rates because of the excess IKI added
intended to test for a color change or other unknown factors.
ÊPaper chromatography was done to determine
what pigments are in each sample (Krha et al. 2004). We predicted that the
normal light plants would produce the highest levels of chlorophyll; the UV
light plants would have the highest levels of carotene; and the no light plants
would have very little pigment if any. After analyzing the strips we found
large amounts chlorophyll in the normal light plants.Ê We found this reasonable because light stimulates
the production of chlorophyll during the light phases of photosynthesis
(Freeman 2002).Ê The UV light plants
showed large amounts of orange β-carotene and yellow carotenoids, which
are produced by plants for protection from harmful light rays (Davidson 2002).
The plants grown in no light had little to no pigment in them (Figure 6).Ê There was no quantitative way to measure
pigment levels.Ê We made these
assumptions qualitatively based on the appearance of our strips.Ê
The action
spectrum was run to determine how well the plants photosynthesized.Ê As photolysis takes place, the solution which
contains blue dye is bleached as a result of the reaction.Ê A greater color change, as determined by
spectrophotometry, indicates that chloroplasts are undergoing more
photosynthesis.Ê We saw that our lowest
absorption readings were for plants grown in the dark, while the UV group had
the second highest, and the white light group had the highest.Ê These results suggest that the plants grown
in the dark were the best at photosynthesizing while the normal light group was
the slowest.Ê To explain these results we
could hypothesize that after going without light for so long this group might
have been preparing to whenever it finally could.Ê Another argument would be that since the
solution made using the white light group was a dark green color to begin with,
while the dark room group was nearly white, the absorption would obviously be
higher and make it seem as though they were photosynthesizing less.
The next
set of test we performed was for the presence of protein. The test we ran was
the Bradford Protein Assay in which we find the concentrations of protein in
the different experimental groups (Krha et al., 2004). Normal light was
predicted to have the highest concentration of protein; UV light would have the
second highest, while no light was predicted to have the least amount of
protein. After performing the test we found the average protein concentrations
for the UV plants to be the highest at approximately 3.85 μg/μl,
normal light plants were the second highest at 2.46 μg/μl , and no
light plants had the least 1.73 μg/μl (Figure 7, Table 6).Ê Protein concentration in UV plants being the
highest suggests that normal cell functions were not taking place.Ê The UV light could have stimulated production
of certain proteins as a defense or perhaps the destructive force of the UV
light damaged the plant so much that extra protein was produced to make
repairs.
After
performing all the different tests, we concluded that the data supported our
hypothesis in nearly all the tests. Many problems arose while performing the
different experiments, however. If this experiment was to be repeated we would
recommend doing more repetitions of each test. Also, some of the tests we
preformed were not conclusive because we could not control factors such as
excess plant residue in our solutions as well as samples that contained plant
components that cause secondary reactions in our experiments.Ê Due to a lack of time, we felt like more
accurate data could have been attained if we had had more time to perform
alternate experiments. Another problem that occurred was not enough time was
allotted for the lima beans to grow reasonable sized plants.Ê Other than these problems, we felt that this
project was very successful in answering our question.Ê
All one
need do is look at the pictures of our plants to see the effects UV light can
have on the environment.Ê If the hole in
the ozone is indeed getting larger what could happen if it where to spread to
places other than the arctic?Ê Without
the protection of the ozone layer dangerous wavelengths of UV light could
destroy crops and forests worldwide leading not only to famine, but
deforestation and the destruction of entire ecosystems.