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Unformatted text preview: 5-1 SPRING 2010 NAME _______________________________ BTNY21SECTION (DAY/HOUR)______________________ LABORATORY #5(PLANT GROWTH REGULATORS AND EXTERNAL FACTORS) Lab #5 Objectives:1) learn about the various affects that the plant hormones, auxin and gibberellic acid, have on plant growth and development 2) study the ways that plants and different plant parts respond to external stimuli such as light, dark, gravity and touch 3) become familiar with the basic mechanism by which auxin causes directional growth Note:In some experiments in this lab we are artificially applying hormones to plants. Keep in mind that these experiments are designed to illustrate the natural effects of the hormones within plants. A. EFFECTS OF HORMONES ON PLANT GROWTH AND DEVELOPMENT 1. Auxin and Apical Dominance The only known naturally occurring auxin is IAA (indoleacetic acid). It is produced at the shoot tip and moves downward toward the base of the plant through vascular tissues. IAA inhibits the development of lateral buds. In other words, if IAA is present at sufficient concentrations, buds will not sprout to produce new lateral shoots. These plants were treated about 14 days ago as follows: Plant 1: No treatment; served as control Plant 2: Stem and growing tip removed. Plant 3: Same as plant 2, except that 1% IAA in lanolin was applied to the cut stem Plant 4: Same as plant 2, except that lanolin alone was applied to the cut stem Examine these plants and describe their appearance, primarily looking for lateral shoot formation on the four plants. Plant 1 (untreated control): Plant 2 (stem tip removed): 5-2 Plant 3 (IAA + lanolin): Plant 4 (lanolin alone): a) What was the effect of the IAA? b) Why was plant 4 treated with lanolin alone? c) Describe apical dominance and how it is maintained. d) If you wanted to get your houseplants to look bushy, with lots of lateral stems, what would you do to them? 2. Auxin and Leaf AbscissionLeaves normally abscise (separate from the stem and fall off the plant) in the fall. The role of auxin in leaf abscission is shown with the following sets of plants. The plants were treated about 7 days ago as follows: Plant 1: No treatment; serves as a control Plant 2: Leaf blades only removed (petioles remain attached to the stem), and 1% IAA in lanolin was applied to the cut ends of the petioles of the first set of fully expanded leaves. Plant 3: Same as plant 2, except lanolin without IAA was used....
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