The Effects of Hypertonic Saline Solutions on the Germination of Mung Beans

Jeremy CummingsVirginia Commonwealth University

BIOZ 151 – L2710/23/2015

Abstract

Salt water intrusion is a growing threat to agriculture across the United States.

Higher levels of salinity in the soil negatively affect plant growth and development,

however little is known about how salinity affects plant germination. The purpose of

this experiment was to address the effects of salinity on the germination of mung

beans.

To test the effects of salinity, hypertonic saline solutions were prepared.

Paper towels were saturated in the solutions, and placed into a sealed bag with

mung bean seeds. The seeds were left in a dark environment for several days to

allow germination to take place. The seeds were examined daily to determine the

rate of germination and the quality of their development.

The data collected did not provide significant evidence to the effects of

salinity on mung bean germination. Unexpectedly, it was noted that beans which

germinated in the 0.05M NaCl solution exhibited faster rates of germination than

any other group. The data collected negated the hypothesis that mung beans

sprouted in hypertonic solutions would display inhibited development.

Introduction

Salt-water intrusion is one of the biggest problems facing modern agricultural. This

experiment was conducted to address the effects of increasing salinity on plants,

and specifically examine how seed germination was affected by hypotonic and

hypertonic solutions. Seed germination is a delicate process, which requires specific

amounts of water, oxygen, appropriate temperatures, and also relies upon specific

light and nitrate conditions. Germination begins with the seed taking up water,

followed by expansion of the embryo within the seed. As the seed continues to take

up water, the cell begins to elongate until eventually emerging as a radicle from the

seed coat. Once the radicle has emerged, germination is considered to be complete

(Finch-Savage, William, and Gerhard, 2006).

Osmosis is defined as net movement of water across a semi-permeable

membrane, due to differences in osmotic pressure. Osmotic pressure is therefore

defined as the minimum pressure that must be applied to a solution to prevent

inward flow of water across a membrane. When solutes are present in a solution,

osmotic pressure is changed (a colligative property of solutions) thus changing the

net movement of water across the membrane. This experiment, 0.5M CaCl2 was used

as the hypertonic solutions. In environments of high solute, organisms, including

plants, die from dehydration due to osmosis (Tzahi , Childress, and Elimelech,

2006).

The growth of various cells in hypertonic and hypotonic solutions has been

examined in various laboratory settings. Cells which are grown in hypertonic

solutions have inhibited growth abilities. On the other hand, cells which were grown

in hypotonic solutions displayed an accelerated rate of growth (Hogue, 1919).

Because hypertonic solutions seem to inhibit cell growth, it is predicted that if seeds

are placed in various hypertonic solutions, that seed germination will be inhibited

by the solution. It is further predicted that plants grown in hypertonic solutions will

exhibit delayed development.

This experiment can help to better understand the problem that salt water

intrusion presents to agriculture, by gaining a better understanding of how the

earliest stages of plant development are affected by salinity. Understanding what

effects salinity has on seed germination can help to alter agriculture practices to

better combat increasing salinity within the soil. This research can also help us to

understand what properties of plants may help them to be better adapted to live in

high salinity environments.

Materials and Methods:

Hypertonic solutions of 0.005M, 0.01M M, 0.05M, and 0.1M NaCl were prepared

using the standard molarity formula: M= molessoluteLiter of solution . A control solution of

deionized water was also prepared. Approximately 3mL of 0.005M NaCl solution

was applied to a single paper towel, which was then placed into a self-seal plastic

bag. This was repeated six times for each of the experimental groups, and 24 times

for the control group.

Ten mung beans were placed into the paper towels within the bag, and the

bag was then sealed. This was repeated for all 48 trials. Each bag was labeled with

the solution it contained. The bags with seeds were then placed into dark rooms at

room temperature (approximately 20-24°C). Each day, the seeds were checked first

thing in the morning, and the number of seeds germinated was counted. A seed was

considered to be germinated when the seed capsule had broken and a radicle had

begun to emerge from the seed. Data was collected over a period of seven days, after

which the average rate of germination, and average daily germination per group

were calculated. Data from each of these calculations were then graphed (Figures 1

& 2).

Data & Results:

Data was collected and compiled into the two figures shown below. Figure 1

displays the average rate of germination by day seven of the experiment; each of the

trials were analyzed and averaged based upon how many seeds germinated by the

seventh day. From the graph, no significant difference in germination is noted

between the experimental and control groups. Figure 1 visually displays the rates of

germination by day 7, with 0.05M NaCl having the highest bar, because it had the

highest rate of germination by day seven.

Table 2 displays the average of how many seeds germinated each day,

broken down by saline solution concentration. The table better demonstrates how

germination occurred over the period of seven days. The Control group had the

quickest rate of germination, with an average of 9.0417 seeds germinating on the

fifth day of the experiment, and 9.917 seven. The next quickest rate of germination

was observed in 0.05M NaCl, with nine seeds germinating by day five, and all ten by

day seven. Figure 2 provides a visual representation of the data from the table. The

line that represents the control and the line representing 0.05M NaCl have steeper

slopes because these trials germinated the quickest. The lines representing 0.005M

NaCl and 0.01M NaCl appear to demonstrate that these trials had the slowest rates

of germination, and germinated at approximately the same rate. Because of the

many similarities between each of the experimental groups and the control group,

the data collected is likely not significant.

0.005 M NaCl 0.01M NaCl 0.05 M NaCl 0.1 M NaCl Control0

1

2

3

4

5

6

7

8

9

10

Salinity Concentration

Ave

rage

Ger

min

atio

n b

y D

ay 7

Figure 1: Average Germination Rate by Day 7

1 2 3 4 5 6 70

1

2

3

4

5

6

7

8

9

10

0.005 M NaCl0.01 M NaCl0.05 M NaCl0.1 M NaClControl

Day

Ave

rage

Nu

mb

er o

f See

ds

Ger

min

ated

Figure 2: Average Germination by Day

Discussion:

The results of the experiment rejected the hypothesis that if seeds were placed into

a hypertonic solution, that germination would be inhibited. The data did not show

enough variation to support the hypothesis; the rates of germination for each of the

differing solutions only varied by <1.0 point, indicating no significant difference

between each of the groups. It was noted however, the rate of germination for the

0.05M NaCl group was slightly higher than that of the control group. Surprisingly,

figure 2 indicates that some of the hypotonic solutions (0.005M NaCl) had slower

rates of germination than that of the more hypertonic solutions such as 0.05M NaCl.

While legumes such as mung beans typically are not tolerant to salinity, the

mung bean has been observed to have the ability to exclude sodium ions from their

shoots out into soil from their roots (Salim, 1988). This may provide an explanation

as to why there was not much variation observed in the groups; if mung beans are

able to tolerate salinity well through salt exclusion, then the presence of saline

would have minimal effects. These findings and the findings of our experiment are

conflicting with the findings of Ashruf and Rasul, who found that mung beans have a

high sensitivity to salt during germination, “due to reduced absorption of water by

the germinating seeds,” (1988).

The solutions in the experiment conducted were of approximately the same

concentrations of those mentioned in literature (Ashruf and Rasul, 1988)(Salim,

1988). However different findings were observed in the experimental germination

rates versus those found in the literature. These findings may possibly be due to the

use of iodized salt to prepare the solutions, rather than solutions of sea salt. The role

iodide ions play in growth of the mung bean is unknown, and could be any area of

further study. While the seeds in the literature were typically grown in a sand

environment, as is the native environment of the mung bean, experimental data

used a damp paper towel medium. The lack of significance between the

experimental groups is possibly due to variation within the natural population.

Because sample size was small, this may have also affected the significance of the

data. To further validate the findings of this experiment, sand medium could be used

for comparison.

The findings of this experiment indicate that salinity neither inhibits nor

promotes the germination of mung beans. As salt intrusion becomes an ever more

worrisome threat to our agriculture, these findings may have important application.

In high salt environments, mung beans could potentially be grown where other

crops are unable to grow, such as coastal areas. Further experimentation is needed

to validate these findings, however if the findings hold true, the agricultural

implications would be vast.

References

Ashraf, M. & Rasul, E. (1988). Salt tolerance of mung beans (vigna radiate (L.)Wliczek). Plant and Soil, 110(1), 63-67.

Cath, Tzahi Y., Amy E. Childress, and Menachem Elimelech. "Forward Osmosis:Prince, Applications and Developments." Journal of Membrane Science 281 (2006): 70-87. Elsevier. 6 June 2006. Web. 15 Sept. 2015.

Finch-Savage, William E., and Gerhard Leubner-Metzger. “Seed Dormancyand the Control of Germination.” New Phytologist (2006): 501-23. Wiley Online Library. 8 Apr. 2006. Web. 15 Sept. 2015.

Hogue, Mary J. "The Effect of Hypotonic and Hypertonic Solutions on the Fibrolastsof the Embryonic Chick Heart in Vitro." Journal of Experimental Medicine (1919): 617-50. Journal of Experimental Medicine. 19 Aug. 1919. Web. 15 Sept. 2015.

Salim, M. (1988). Loss of Sodium from Mung Bean Shoots to Saline RootMedia. Journal Of Agronomy & Crop Science,160(5), 314-318.