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Lecture 19

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SOC 205
Ingrid L.Stefanovic

Phototropism:, Blue light absorption Red light absorption VS. Far red light absorption Controls the growth of stems towards the light(phototropism) Determines : a)seed germination b)stem and root Role and the opening of stomata growth c) flowering time -play role in photodormancy (plants that require activation by light) Photoreceptor: phototropin Phytochrome Pathway: 1) A flavin containing protein, phototropin, absorb blue light  Photo morphogenesis: effects of light on plant 2) After absorption of blue light, phosphate is added to growth and development phototropin which initiates a signal transduction pathway  Phytochrome: the photoreceptor that absorbs leading to movement of auxin to the dark side of the stem light and causes developmental effects 3) This movement stimulates growth on the dark side of  Pigment exists in 2 shapes, When exposed to red coleoptiles, causing movement of stem toward light light, photochrome is converted to a form that absorbs far red light (Pfr). When exposed to far Phototropin is similar to other proteins that help detect light, red light, the phytochrome is converted to a form oxygen and voltage (LOV DOMAIN) that absorbs red light, Pr. autophosphorylation of 2 membrane proteins,  Photoreversibility occurs because light absorption Phototrophins 1 & 2) makes photoreceptor pigment change shape  PFR is the on switch, thus red light causes roots have a greater sensitivity to auxin (negative developmental effects , PFR form results in seed phototropism vs positive phototropism), concentrations of germination, PR form inhibit seed germination auxin that promote shoot growth, inhibit root growth  R wavelengths drives photosynthesis, but FR light is not absorbed by photosynthetic pigments ;When plants are shaded, more FR filters through leaves and is absorbed by plant , shaded plants promote stem elongation ;photdormacy can be overcome by exposure to red or far red light, gibberellins, cold treatments, or by removing seed coat and endosperm to expose the embryo Protein structure: -protein structure of phototropins 1 & 2 consist of:  Included genes involved in greening of leaves, a) Flavin mononucleotides binding domains and expression of several key proteins in b)Kinas Domain: phosphorylate serine/threonine amino acid photosynthesis residues in target substrate , auto phosphorylate Photoperiodism:  Define: photoperiodism is any response by an organism that is based on photoperiod, the relative lengths of day and night o To determine what time of year plants grow and flower, plants integrate many environmental cures o In response to changes in photoperiods plants can alter their development and switch to flower production  Role: regulates flowering and other seasonal responses  Researchers discovered plants measured the night length and not daylength o Therefore it would be more
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