This exercise is one of preparation and therefore will not be handed in at any time. Keep this in your notebook, and use it as directed by the instructor.
The apex of a plant produces hormones that signal the lateral buds of the plant to remain dormant. At the beginning of the term you planted pea seeds in four pots. Retrieve those pots; their pot labels should have your group name and the words "pruning" on them.
Observe how many plants are growing in each pot. Remove plants as needed so that the same number of plants remain in each pot. Selectively remove the abnormally large or small plants as you do this. When you are finished, the plants in each of the four pots should be about the same size and should be the same in number.
Mark the label of the first pot "Intact."
Mark the label of the second pot "Decapitated." Decapitate each plant in this pot just above the first compound leaf, as directed by your instructor. There should be an obvious terminal stem stub extending beyond the last node.
Mark the label of the third pot "Lanolin." Decapitate the apical bud from each plant in this pot as before. Then, using a toothpick, apply a small dollop of plain lanolin paste to the terminal stem stub of each plant.
Mark the label of the fourth pot "IBA." Decapitate the apical bud from each plant in this pot as before. Then, using a toothpick, apply a small dollop of 5000 ppm IBA in lanolin paste to the terminal stem stub of each plant.
Return your four labeled pots to the designated area of the greenhouse bench and put them on-line with the watering system.
Gibberellic acid (GA) is a plant hormone involved with the elongation of stems. In tall varieties of peas much GA is produced by young leaves and it causes the stem to elongate. Dwarf varieties of peas are believed to produce very little GA. B-9 is a potent inhibitor of the natural production of GA in pea plants.
Retrieve your eight pots of pea plants labeled with your group name and "growth hormones." Sort out the four pots of tall peas from the four pots of dwarf peas. This experiment must be carried out IN SEQUENCE as described below:
Label the first pot of each variety (dwarf and tall) as "Untreated." Return these two pots to the greenhouse bench and put on-line with the watering system.
Label the second pot of each variety (dwarf and tall) as "Water." Spray the plants with detergent water until they drip with it. Return these two pots to the greenhouse bench and put on-line with the watering system.
Label the third pot of each variety (dwarf and tall) as "GA." Spray the plants with 10-4 M GA until they drip with it. Return these two pots to the greenhouse bench and put on-line with the watering system.
Label the fourth pot of each variety (dwarf and tall) as "B-9." Water the soil in each pot with 75 mL of 0.5% B-9 Drench (2t/l). Add the solution very slowly so it can be taken into the soil without running out the bottom of the pot. Return these two pots to the greenhouse bench and put on-line with the watering system.
Retrieve your two pots of mung beans planted in vermiculite from the greenhouse. Take them to the classroom (Shafer 215).
Prepare four cups:
Label each cup with the treatment and your group name. The four treatments are: "0 M IBA," "10-7 M IBA," "10-5 M IBA," and "10-3 M IBA."
Put 20 mL of the corresponding solution into each of the four cups. Be careful that you use the correct graduated cylinder to measure this volume; even the tiny drops adhering to the glass would influence the concentration if you mixed up the cylinders. Read the labels and use the correct one. If you make a mistake, call the instructor immediately!
Carefully uproot the seedling to minimize any damage to the stems. Examine the seedlings to find the cotyledonary node (maybe with shriveled cotyledons attached) and the two opposite pointed primary leaves at the node just above. Remove the cotyledons if they are still attached.
Using a razor blade carefully cut off the root system with a cut located 1 or 2 cm (ask your instructor which!) below the cotyledonary node. Immediately stand the stem cutting in one of the prepared cups. Continue this step until each cup contains ten stem cuttings. Put the cups in the designated area under the fluorescent lights.
Return any undisturbed pots to the greenhouse. Put the used pot contents and any other plant debris into the compost bag as designated by your instructor. Clean up all vermiculite from the table surface (you might have to scrub a little). Discard all labels from the empty pots, rinse out the inside of the pots, and return the clean, empty pot to the designated area.
This page © Ross E. Koning 1994.
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