Seed Germination
In this exercise you will learn about propagating plants sexually (from seeds). Pay careful attention to your instructor on the use of Petri dishes. Every group should carry out the non-majors project described here with tomato juice and the various light treatments. This requires six petri dishes to be prepared and placed in the correct conditions. Then each group should do something to shed some light on mechanisms of why the sample results occurred or how the results can be circumvented.
I. The effect of fruits on seed germination.
In a non-majors course, three Petri Dishes were lined with one disc of filter paper. The bottom is the smaller of the two dishes and fits inside the cover. Put 5 ml of distilled water in the first dish, 5 ml of tomato juice in the second dish, and 5 ml of 1 mM Abscisic Acid in the third dish.
50 lettuce seeds were counted carefully and placed in each dish on top of the moist paper. The
three dishes were placed under the lights to allow the seeds to germinate.
| After 3 days | After 6 days
|
|---|
| Water + light | 80% | 90%
|
| Tomato juice + light | 0% | 0%
|
| 1 mM Abscisic acid + light | 0% | 0%
|
It would be interesting to know what caused the tomato juice to inhibit seed germination. What are some of the possibilities?
- The project seems to lead you into the idea that it is due to Abscisic acid. One group might do a dose response of Abscisic Acid to check out this variable. Use factors of ten between treatment concentrations. All dishes should be placed in the light!
- Tomato juice is sweet and probably contains lots of sugar. One group might check the osmolarity of tomato juice with the osmometer, and then prepare a dilution series of 1 M sucrose that encompasses that osmolarity.
- Tomato juice also is acidic (sour tasting). One group should determine the pH of tomato juice, and prepare a series of buffers over a range including the pH of of tomato juice. A recipe follows:
| pH | mL 0.1 M
Citric Acid | mL 0.2 M
K2HPO4
|
| 3.0 | 4.0 | 1.0
|
|---|
| 4.0 | 3.1 | 1.9
|
|---|
| 5.0 | 2.4 | 2.6
|
|---|
| 6.0 | 1.8 | 3.2
|
|---|
| 7.0 | 0.9 | 4.1
|
|---|
| 8.0 | 0.1 | 4.9
|
|---|
II. The effect of light on seed germination.
In the non-majors course, similar preparations (all with water) were made, but the dishes were placed under different light sources. The dishes for the dark treatment were wrapped immediately in aluminum foil.
After counting on the third day, all dishes were put in white light for three days.
| After Three Days | After Six Days
(~ 3 days in white light)
|
|---|
| Treatment | Germination (% of 50) | Germination(% of 50)
|
|---|
| Water in red light | 85 % | 95 %
|
| Water in far-red light | 2 % | 60 %
|
| Water in darkness | 30 % | 80 %
|
The light effects could also be "dissected" some.
- The elimination of germination under far-red light is pretty impressive. A group might see whether GA can overcome this effect. A dose response could be prepared with factors of ten between concentrations. All dishes should be placed under far-red light.
- Another group might determine whether the dark-inhibition can be overcome by gibberellic acid. The factors of ten dilution series could be prepared, but all dishes should be wrapped in foil.
Another dormant seed
Also available is a limited supply of Crotalaria (rattlepod) seeds. Select forty seeds. Put twenty in each of two dishes just as you did for lettuce. Use plain distilled water. We will observe later to see what happens.
After three days, use dissecting needles to perform a needed operation (scarification). Then observe after three more days.
HELP!
This week we need one volunteer from each group to meet me at the greenhouse to spray some plants for a future lab. It needs to be done THIS WEEK and SOONER rather than later. Today would be GREAT!
Go back to the Course Schedule.