Phototropism

) is regulated by blue to UV light , a fungus, also exhibit phototropismPhototropism is directional plant growth in which the direction of growth is determined by the direction of the light source. Phototropism is one of the many plant tropisms or movements which respond to external stimuli. Growth towards a light source is a positive phototropism, while growth away from light is called negative phototropism . Most plant shoots exhibit positive phototropism, while roots usually exhibit negative phototropism, although gravitropism may play a larger role in root behavior and growth. Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them.Phototropism in plants such as Arabidopsis thaliana is regulated by blue light receptors called phototropins. Other photosensitive receptors in plants include phytochromes that sense red light and cryptochromes that sense blue light. Different organs of the plant may exhibit different phototropic reactions to different wavelengths of light. Stem tips exhibit positive phototropic reactions to blue light, while root tips exhibit negative phototropic reactions to blue light. Both root tips and most stem tips exhibit positive phototropism to red light. Phototropism is enabled by auxins. Auxins are plant hormones that have many functions. In this respect, auxins are responsible for expelling H+ ions which decreases pH in the cells on the dark side of the plant. This acidification of the cell wall region activates enzymes known as expansins which break bonds in the cell wall structure, making the cell walls less rigid. In addition, the acidic environment causes disruption of hydrogen bonds in the cellulose that makes up the cell wall. The decrease in cell wall strength causes cells to swell, exerting the mechanical pressure that drives phototropic movement. (From the Wikpedia article Phototropism.)

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Recent Publications on Phototropism:
Distribution and phylogeny of the blue light receptors aureochromes in eukaryotes. The new type blue light (BL) receptor aureochrome (AUREO) was recently...	3rd November, 2009	Graduate School of Life Sciences, Tohoku University, Sendai, 980-8577,	Planta. 2009 Aug;230(3):543-52. Epub 2009 Jun 21. DOI Direct Link
Analysis of the phytochrome gene family in Ceratodon purpureus by gene targeting reveals the primary phytochrome responsible for photo- and polarotropism. Using gene targeting by homologous recombination in Ceratodon purpureus,...	3rd November, 2009	Department of Plant Physiology, Justus Liebig University,	Planta. 2009 Jun;230(1):27-37. Epub 2009 Mar 28. DOI Direct Link
Two seven-transmembrane domain MILDEW RESISTANCE LOCUS O proteins cofunction in Arabidopsis root thigmomorphogenesis. Directional root expansion is governed by nutrient gradients, positive...	29th October, 2009	Department of Biology, University of North Carolina, Chapel Hill, North	Plant Cell. 2009 Jul;21(7):1972-91. Epub 2009 Jul 14. DOI Direct Link
Conformational heterogeneity and propagation of structural changes in the LOV2/Jalpha domain from Avena sativa phototropin 1 as recorded by temperature-dependent FTIR spectroscopy. Phototropins control phototropism, chloroplast movement, stomatal opening,...	14th October, 2009	Department of Biophysics, Faculty of Sciences, Vrije Universiteit, 1081HV	Biophys J. 2009 Jul 8;97(1):238-47. DOI Direct Link
Distribution and phylogeny of light-oxygen-voltage-blue-light-signaling proteins in the three kingdoms of life. Plants and fungi respond to environmental light stimuli via the action of...	29th September, 2009	Institut fur Molekulare Enzymtechnologie, Heinrich-Heine Universitat	J Bacteriol. 2009 Dec;191(23):7234-42. Epub 2009 Sep 25. DOI Direct Link
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Phototropism Patents:
US Patent No.	Title
5424255	High-refractive index phototropic glass
6114503	Human blue-light photoreceptor hCRY2
6160617	High resolution imaging microscope (HIRIM) and uses thereof
6245717	Suppression of auxin in higher plants
6255466	Purified plant expansion proteins and DNA encoding same
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