The Effect of Green Tea and Deionized Water on the Growth Rate and Chlorophyll
Concentration of Catharanthus roseus
Brett Niles and Carlin Harkness
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
Green tea has many claims to its health benefits on humans. In this experiment, we
tested whether green tea had health benefits to plants. The relationship between green tea,
deionized water, and tap water was determined by measuring the growth rates and
chlorophyll concentration of three groups of Catharanthus roseus that were watered with
the respective mediums. Stem diameters were measured twice a week and chlorophyll
concentration was measured by spectrophotometry. The resulting data showed no
significant difference in growth rates and chlorophyll concentration data was inconsistent.
Therefore, null hypothesis was supported. There were external factors including aphid
infestation which might have contributed to our inconsistent results.
Introduction
Extensive research has gone into studying the effects of green tea on humans and
animals. However, if out there, official research on the effects of green tea on plants is scarce.
Also, there is much media on the health benefits of green tea, mostly concerning the antioxidant
properties. Some advocates of green tea make strong claims that it can cure rheumatoid arthritis,
reduce body fat, cure gastric ulcers etc. (Johnson 2009). Other research has shown that green tea
consumption may reduce the risk of leukemia (Kuo 2008). The consumption of green tea has
also been repeatedly shown to play a protective role against liver disease and may lead to a
reduced risk of liver disease (Jin 2008). However, research of green tea consumption and cancer
is less conclusive. Most studies showed no relationship between green tea consumption and
cancer, and few showed that green tea consumption was associated with a decreased cancer risk
(Sturgeon 2009). The one thing in common with most studies is that they attribute the beneficial
qualities to certain chemicals that are contained in green tea. These chemicals are found in the
tannins released from the tea leaves when it is steeped in hot water. Tannins contain polyphenols
and flavonoids which are subgroups that contain the antioxidative chemicals that are the source
of beneficial health effects. Catechins are one of the classes of flavonoids also called flavin-3ols. The specific catechin that is known for its potent antioxidant properties is epigallocatechin
gallate (EGCG).
Plants along with many other organisms produce free radicals as byproducts or
intermediates of metabolic pathways. In plants, photosynthesis is a major producer of free
radicals (Uri 1955). In order to counter the free radical intermediates, plants must also produce
antioxidants; this is the source of catechins that is acquired from tea when consumed. Therefore,
if human consumption of tea possesses many health benefits, then it seems reasonable to
presume that it will have similar effects on plants. Our objective was to determine if there was a
relationship between plant health and different watering mediums including: green tea, deionized
water, and the control group with tap water. We hypothesized that Catharanthus roseus watered
with green tea would have improved health and therefore increased growth rates and chlorophyll
concentrations compared to Catharanthus roseus watered with tap water and that Catharanthus
roseus watered with deionized water would have worse health and therefore decreased growth
rates and chlorophyll concentrations compared to Catharanthus roseus watered with tap water.
Methods
We began with young Catharanthus roseus in three groups of ten each: a green tea group,
deionized water group, and the control group with tap water. We used soil from same bag and
pots, both provided by Saddleback College. The Catharanthus roseus was purchased from Green
Thumb International Nursery in crates of 16 plants per. The plants were kept in the greenhouse
at Saddleback College in a controlled environment. The experiment lasted for five weeks.
Measurements of stem diameter were taken using a digital caliper at location level with the top
of the pot. These measurements were taken about twice a week for the duration of the
experiment. Also, we noted any plants whose health appeared compromised or if the plant
appeared deceased. Each group was watered with the three different mediums: green tea,
deionized water, and tap water five days a week for the first week. However, due to soil
conditions from this watering frequency being detrimental to the health of the plants and in
attempt to use optimal conditions for the experiment, we watered them four days a week for the
remainder of the experiment. Each plant received 50 ml of watering medium when watered. An
attempt to determine chlorophyll concentration was done with leaf samples taken in the third and
fifth week of the experiment. We used methods derived from other research experiments that
determined chlorophyll concentration by photospectroscopy (MacKinney 1941, Cate et al. 2003).
These leaf samples were then measured out to 0.2 g of leaf material per group and added to 15
ml of 80% acetone solution and left overnight in 4ºC in the dark. Absorbance of the acetone
solution containing the chlorophyll was then taken. The absorbance was taken for each group
first at 940 nm wavelengths as a reference and then at 660 nm. We used ANOVA tests on the
stem diameter data and for the chlorophyll concentration absorbance data a ratio was taken to
determine chlorophyll content index (CCI).
Results
An analysis of variance (ANOVA) single variable test was performed on the average
values of stem diameters for each day of measurement. This first test included the measurements
of healthy and unhealthy or dead plants. Green tea did not significantly increase health and
deionized water did not significantly decrease health of Catharanthus roseus (p=0.44) compared
to the control group. The average stem diameters for each day measured was plotted over time
and is shown in figure 1. Then we performed another ANOVA single variable test on the data
with the unhealthy and dead plants omitted. Again, green tea did not significantly increase health
and deionized water did not significantly decrease health of Catharanthus roseus (p=0.69)
compared to the control group. Also, the average stem diameters for this modified data were
plotted over time and are shown in figure 2. The CCI values should be between 1 (no
chlorophyll) and 70 (very high chlorophyll), but our CCI values were far above 70. The lowest
CCI for any group was 96 and went as high as 1000.
Discussion
We did not find a significant effect of green tea or deionized water on the health of
Catharanthus roseus compared to the control group in this experiment. This could be due to
many factors. The one that appears most obvious is the infection of several of our plants in the
green tea group with aphids. Seven of our plants in the green tea group were infected with aphids
by the end of the experiment. This infection spread to the deionized group and tap water group
also, but to a less severe degree. By the end of the experiment, only two of the green tea group
and seven of the deionized group were still alive. Another factor to consider is the spoiling of the
green tea after about a week. The first batch of green tea spoiled after a week, it emitted a foul
odor and became turbid. A second batch was made after two weeks; however, it also became
spoiled after a week and no more green tea was made after this. Whether or not this could affect
the plants is unknown, but should be considered. Furthermore, green tea is richer in chemical
constituents compared to tap water. Green tea contains the minerals zinc, manganese, and copper
which are essential for plant growth and required in trace amounts. Too much of these minerals
can have detrimental effects on plant growth. Furthermore, an abundance of these minerals in the
soil can make it more difficult for the plant to take in other needed nutrients. A similar result of
the harmful effects of longer exposure to green tea has been observed (Webb 2000). Therefore,
green tea may have been beneficial in a shorter duration, but eventually became harmful to the
plants in our green tea group.
The chlorophyll concentration data for this experiment was invalid according to the
parameters of the resulting values. Our method for determining the chlorophyll concentration
may have been incorrect. To produce usable data for chlorophyll concentration, a chlorophyll
content meter could be used. The chlorophyll content meter is a handheld device that measures
chlorophyll concentration automatically. However, these measuring devices may be out of the
budget of some researchers. Therefore, a better method similar to the one used in this experiment
may be necessary.
Future research may approach this experiment by watering the green tea group in
alternating periods of green tea and tap water. This could possibly utilize the nutrient rich green
tea more effectively and not overdose the plants on certain nutrients. Also, measures should be
taken to prevent the infection of aphids and use of pesticides of infection occurs.
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