Seed Germination

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Seed Germination

The basic idea of this project is to try to understand why seeds do not germinate inside a fleshy fruit (such as a tomato), where the warm and moist conditions favorable for seed germination exist. How does the juice of the fruit inhibit seed germination? Could it be the pH of the juice? the osmolarity? the presence of an inhibitory compound, such as abscisic acid?

To model this question, we note that the germination of lettuce (Lactuca sativa) is inhibited in tomato juice. Three possibilities seem plausible which we shall test. The fruit juice environment contains too much solute (mostly sugar) for the seeds to sprout. The fruit juice environment could have an inappropriate pH (likely too acidic) for the seeds to sprout. The fruit juice contains too much Abscisic acid (ABA) for the seeds to sprout. If there are sufficient teams available, we shall also test the ability of gibberellic acid (GA) in the fruit juice to overcome the inhibitory effect of darkness and far-red light exposure.

Petri dishes will be used as a chamber for seed germination. The bottom should be lined with a single disc of filter paper moistened with 5 or 6.75 mL of some test solution; the volume used should be the same among your group’s choice of approach. A group of 50 seeds should be sprinkled over this paper. Except for the possible GA study the dishes should be incubated in white light. For the GA study a far-red light source and appropriate filter or aluminum foil are available to provide reasonably monochromatic far-red light and darkness.

In the case of hormones, a 1 mM ABA and/or GA solution and distilled water are available for 1:9 serial dilutions:

For testing osmolarity, a 1 M sucrose stock solution is available for one group; tomato juice for another group. In the Petri dishes, make solutions with 5 mL total volume; starting with 5 mL of stock solution at one end of the concentration scale and 0 mL of stock at the other end, decreasing by 0.5 mL at each step (11 dishes total).

For testing pH, the components for making different pH buffers (citric acid and phosphate) are available for one group:

After at least 3 days of incubation, the number of seeds germinated should be recorded for each treatment and the percentage of seeds germinating should be calculated.

A sample of tomato juice will be available for us to test germination (as a comparator in the seed germination trials). It will also be useful for testing its osmolarity and pH with the vapor pressure osmometer and the a pH meter. For a GA test, perhaps a trial with tomato juice as the diluent should be the focus of at least one group.

You should prepare a proper Biology-publishable quality (Not Microsoft “cute”) graph with caption. Then write a suitable caption for your graph. Write an abstract of your project and attach it to the front of your graph with caption. Hand in your amplified abstract by the due date.

Tomato Juice Osmolarity:______M and pH:______