BILD 2 Chapter Notes - Chapter 31: Petal, Photoperiodism, Gravitropism
8 Dec 2015
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As soon as the darkness passes a critical length, it flowers. With an interruption (flash of light), the plant doesn"t reach its critical length and does not flower: long-day/short-night: plant flowers when the continuous darkness is shorter than the critical length. This is just like flashing r on its own. Result: coleoptile only bends with transparent cap or with opaque shield over curvature (does not bend with opaque cap) The phototropic bending, however, occurred at a distance from the site of light perception (the tip). Boysen-jensen"s results suggested that the signal for the bending is a light-activated mobile chemical: frits went i. ii. removed coleoptile tip and placed it on a cube of agar. The growth- promoting substance diffused into the agar. A block that was centered on top of the coleoptile caused it to grow straight up. When the block was placed off center, coleoptile bent away from side with agar block (growing toward light).
