Desert Plant Lab

8/11/2019 Desert Plant Lab

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Desert

PlantDesign

Lab

How will simulated

drought conditions

affect soybean

growth?


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I.

Question

How will simulated drought conditions affect soybean growth?1

II.

Hypothesis

Soybeans allowed to germinate under regular moisture conditions will demonstrate more radical growth

during the 168 hour (seven day) growth period than beans germinated under simulated drought

conditions. Adding glycol to the growing medium will alter osmotic pressure to mimic drought-like

conditions.

III. Variables and Controls

Table 1 identifies the experiments independent and dependent variables and noteworthy controlsIndependent variable Glycol concentration/osmotic pressureVarying proportions of water and

glycol were used to alter the osmotic pressure in the seeds.

Dependent variable Radical lengthLength in centimeters was measured using a twist tie bent to

follow radical growth and measured straight against a ruler.

Controls Exposure to lightThe petri dishes were placed under a grow light

Mineral composition of waterOne tap water source was used for

all petri dishes

Temperature of waterOne tap water source was used for all petri

dishes (10C)

1Several studies provided background and expected behavior information:

Drought Stress and Tolerance in Soybean (Yee-Shan Ku, Wan-Kin Au-Yeung, Yuk-Lin Yung,

Man-Wah Li, Chao-Qing Wen, Xueyi Liu and Hon-Ming Lam),

http://www.intechopen.com/download/get/type/pdfs/id/40090

How Soybeans Respond to Drought Stress (Roger Borges),

http://www.uwex.edu/ces/ag/issues/drought2003/soybeansrespondstress.html


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IV.

Materials

Four plastic petri dishes

White paper towel, cut to four 6

squares

7 mL polyethylene glycol (PEG)

10 mL graduated cylinder

1 mL pipette

12 soybean seeds

33 mL tap water

Grow light

Centimeter ruler

Plastic twist tie

Latex or nitrile gloves and safety

goggles (glycol is an irritant)

V.

Procedure

1.

Four petri dishes of different growth solution were prepared (10mL water:0 mL glycol, 9mL

water:1mL glycol, 8mL water:2mL glycol, 6mL water:4mL glycol)2. Glycol was added with a

pipette to water in a graduated cylinder. A paper towel square was scrunched up and used to

cover the opening of the graduated cylinder. The cylinder was then shaken to combine the

water and glycol, and the solution was poured into the paper towel square until all liquid was

absorbed.

2.

Three soybeans were placed into each of the four petri dishes. They were completely enveloped

in the saturated paper towel.

3.

The petri dishes were placed under the grow light for a total of 168 hours, with observations

made three times during this period.

4.

Radical lengths for all soybeans were recorded to the tenth of one centimeter. The plastic twist

tie was bent to follow the shape of the radical, then straightened and measured against a ruler.

2The idea to use glycol to simulate drought condition by regulating osmotic pressure with glycol comes

from the study Weed Seed Germination Under Stimulated Drought by Hoveland and Buchanan. The

authors in turn took inspiration from the PEG method used by Parmar and Moore (1965).

http://www.jstor.org/discover/10.2307/4042002?uid=3739920&uid=2&uid=4&uid=3739256&sid=2110

3542823177


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VI.

Data and Presentation

Table 2 presents quantitative data of radical length (raw and averaged) at three times.

Date Hours since

water added

10:0 radical

length (cm)

9:1 radical

length (cm)

8:2 radical

length (cm)

6:4 radical

length (cm)

3/4 24 0, 0, 0 (avg: 0) 0, 0, 0 (avg: 0) 0, 0, 0 (avg: 0) 0, 0, 0 (avg: 0)

3/7 96 0, 1.4, 1.8

(avg: 1.1)

0, 0, 0 (avg: 0) 0, 0, 0 (avg: 0) 0, 0, 0 (avg: 0)

3/10 168 1.6, 4.6, 5.9

(avg:4.0)

0, 0, 0 (avg: 0) 0, 0, 0 (avg: 0) 0, 0, 0 (avg: 0)

Average values were calculated as follows:

For example, the average value in the 10:0 group after 96 hours was calculated as follows:

The resulting averages are listed in Table 2. These values were then plotted in Figure 1.

Figure 1 shows average radical growth plotted against time since water was added.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 50 100 150 200

Averageradicalgrow

th(cm)

Time since water added (hours)

Average radical growth

10:0 group

9:1 group

8:2 group

6:4 group


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Figures 2-5 show the petri dishes after 24 hours. The control group shows healthy development with the

radical about to emerge. The 9:1 group looks as if it will burst as well, but by the end of the experiment,

the radicals had not emerged. The 8:2 and 6:4 groups with glycol show early signs of shriveling that

became more pronounced for the duration of the experiment.

VII.

Conclusion and Evaluation

Only the seeds in the 10:0 group produced radical growth during the 196-hour period. While

some swelling of the seeds in the 9:1 group was observed, no radical formed. Though additional

recording times would be necessary to verify the trend, it appears that the growth in the 10:0 group

followed an exponential growth pattern. The experiment produced very limited data, making further

analysis difficult. It is therefore necessary to complete a follow-up experiment with a modified

procedure.

In the follow-up experiment, the seeds should be germinated in water to develop initial radical

growth. Based on the data in the 10:0 group, this should take approximately 25 to 100 hours. Only after

they have sprouted should they be subjected to the water-glycol solution used in this study. This new

procedure will assume that, in the simulated drought, the seeds had access to enough water to

germinate, but further water supply was reduced.

Apart from the aforementioned, the experiment design seemed effective. The paper towels

provided an excellent growth medium; even after 196 hours, the paper towels (including the water

control group towel) retained enough moisture to keep the seeds from entirely drying up in their

proximity to the grow lamp. This being said, the fact that the moisture was contained in this small area


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did lead to some mold formation. The mold appeared toward the end of the experiment and only

affected the paper towel in the 6:4 group. No mold was present on the seeds themselves.

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