Observations: You have doubtless observed autumn leaves abscising, or perhaps you have had to rake the many piles after the process was over. In lecture you have observed that fruit ripening, leaf senescence, and development of the abscission layer are interrelated and parallel in design.
Question: Do plant growth regulators play any role in the maintenance or hydrolysis of the abscission layer in leaves?
Hypothesis: Hormones may stimulate the maintenance of the abscission layer in leaves.
Prediction: If the hypothesis is true, then petioles should fall off the plant when their maintenance hormone is no longer delivered to the abscission zone.
Experiment: Coleus blumei plants were cultivated to maturity in the greenhouse and pinched to induce many branches. Available to you are plain lanolin, various lanolin pastes containing growth regulators, toothpicks, razor blades, paper, scissors, and hand punch.
Design a project of your own choosing. You might consider cutting off the blade (potential source of hormones) and replacing it with some PGR. You might screen a battery of PGRs. You might consider a chemical ÒdecapitationÓ rather than a surgical treatment. You might consider different points of application to the petiole (basal, apical).
Do not forget about replicates and suitable controls!! Mark each treated leaf with a paper tag fashioned with an opened punch hole to wrap around the stem. Use pencil on the label (remember inks run if wet and fade in the sun).
After a suitable incubation period (several days), observe any petioles that have already abscised. Tap very lightly any remaining petiole to determine the strength of its attachment.
Analysis: Score each replicate 2 if the petiole has fallen off on its own. Score each replicate 1 if the petiole is attached but fell off with a light touch. Add no score (0) if the replicate has its petiole still firmly attached. Get a total score for each treatment and control.
Decision: on the hypothesis:
Go back to the Course Schedule.