Lecture 22 bild 2

Lecture 22 bild 2 - Lecture#22 Endocrinology III Plant...

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Lecture #22 Endocrinology III – Plant Hormones I) Auxin: plant “hormone” a. Structure: indole acetic acid b. Effects i. Phototropism: growth of shoots toward sunlight ii. shoot geotropism: growth of shoots away from gravity iii. root geotropism: growth of roots towards gravity iv. Other: inhibits lateral buds; induces fruit formation c. Mechanism: change [Auxin] change [cell growth rate] Figure. 39-6 as evidence i. Phototropism: tip of growing shoot (coleoptiles) contains auxin; light moves auxin away. Diagram shows: Therefore, Auxin moves away from light, down the far side of shoot where it induces those cells to grow faster, tipping the shoot towards the light source ii. Shoot Geotropism: auxin collects along bottom side of shoot accelerates cell growth there; tips shoot upwards (diagram shows this) iii. Root Geotropism: gravity turns roots down; 1. sensitivity range to auxin (graph ask for it): in roots low auxin concentration increase growth rate whereas very high concentration inhibit growth rate. Therefore, different plant parts have different auxin sensitivity effects.
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