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Topic: Gravitropism

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Root

	Gravitropism - Wikipedia, the free encyclopedia
		The root cap is vital for gravitropism since it contains cells with sensors called statoliths, which are amyloplasts packed with starch.
		This model postulates that the interaction of falling amyloplasts with the structural integrity of the cell is responsible for gravitropism.
		There are cultivars known that are mutants for mechanisms thought to be required for gravitropism.
	en.wikipedia.org /wiki/Gravitropism (1036 words)

	Gravitropism - how it should be measured
		Gravitropism is caused by unequal rates of elongation at different positions across the radial axis of an organ.
		Consequently the ideal method of measuring gravitropism is to assess the rates of cell elongation at various positions in an organ before and after gravitropic stimulation.
		Very often one end of an organ is regarded as a fixed point and is held at a particular angle with respect to the gravity vector so that the free end of the curving organ is then referenced to the fixed point or to the gravity vector.
	www-users.york.ac.uk /~drf1/gsa_1.htm (741 words)

	GraPhoBox NL-Taxivlucht
		Gravitropism is initiated by starch sedimentation in plant cells.
		Gravitropism has mostly been investigated with the use of clinostats, but barely in the microgravitational conditions of space.
		Because gravitropism is one major component of the directional growth of the plant, it’s obvious to try to establish if this system influences the effects of phototropism, the other major directional component.
	www.desc.med.vu.nl /NL-taxi/GraPhoBox/GPB-page1.htm (1509 words)

	Gravitropism
		The initial phase of gravitropism, that of perception, probably involves the root cap and, within the cap, the columella cells have been considered for some time to contain the gravity detecting mechanism.
		Although there is some controversy as to the exact mechanism, the popular model describes the settling of cell components with sufficient mass (e.g., amyloplasts or nucleus) on the bottom of the cells to trigger a pressure-sensitive effect from the ER or plasmelemma.
		There are some similarities, however, since in both cases the kinetics of the gravitropic response reportedly are alike, and since Ca is always redistributed on the side of slow growth whereas auxin is always on the lower sides (although auxin induces two opposite effects on stem and root cells).
	www.inclinehs.org /smb/gravitropism.htm (4918 words)

	Cytoskeleton and IAA
		The Cholodony-Went hypothesis for gravitropism suggests that differential elongation between opposite flanks of graviresponding organs is linked to auxin transport, concentration, and/or sensitivity of the responding tissue.
		The contrasting effect of MT depolymerization on root and shoot gravitropism and auxin transport is unclear but suggests either that roots and shoots have different cellular mechanisms for gravity response or they differ in their sensitivity to MT disruption.
		Gravitropism of the primary root of maize: a complex pattern of differential cellular growth in the cortex independent of the microtubule cytoskeleton.
	www.ucs.louisiana.edu /~khh6430/taxol-iaa.html (5467 words)

	Two explanations have been proposed: (Site not responding. Last check: 2007-10-08)
		I- In 1990 and 1992, Okada and Shimura proposed that root waving is the result from interraction between Gravitropism and Thigmotropism.
		Gravitropic sensitivity provides thigmostimulation by giving the root a tendency to grow into the agar.
		Root growth is described as a growing helix (circumnutation) along the vector of gravity (gravitropism) which is continuously switches growth direction when the root tip touches the agar surface.
	www.tau.ac.il /~ecology/virtau/5-Tali_S/explan.html (86 words)

	vithaabst_meetings
		Root phototropism and gravitropism in wild-type and starchless mutants of Arabidopsis
		To determine the contribution of phototropism to the measurement of apparent root gravitropism, various measures of gravitropism were performed so that the responses with light from above or below were compared in the WT and in the starchless mutants pgm-1 and adg1-1 (TL255) of Arabidopsis.
		Gravitropism and tissue-specific phenotypes in plastid starch and sedimentation in the Arabidopsis sex1 mutant
	www.msu.edu /~vitha/vithaabst_meetings.html (1170 words)

	Plant graviperception and gravitropism: a newcomer's view -- RANJEVA et al. 13 (9001): 135 -- The FASEB Journal
		Gravitropism is an adaptable mechanism corresponding to the
		Baluska, F., Hauskrecht, M., Barlow, P. W., Sievers, A. (1996) Gravitropism of the primary root of maize: a complex pattern of differential cellular growth in the cortex independent of the microtubular cytoskeleton.
		Lu, Y-T., Feldman, L. (1997) Light-regulated root gravitropism: a role for, and characterization of, a calcium/calmodulin-dependent protein kinase homolog.
	www.fasebj.org /cgi/content/full/13/9001/S135 (4257 words)

	Involvement of the Vacuoles of the Endodermis in the Early Process of Shoot Gravitropism in Arabidopsis -- Morita et ...
		Gravitropism is an important environmental response in plants.
		Fukaki, H., Fujisawa, H., and Tasaka, M. The RHG gene is involved in root and hypocotyl gravitropism in Arabidopsis thaliana.
		Weise, S.E., and Kiss, J.Z. Gravitropism of inflorescence stems in starch-deficient mutants of Arabidopsis.
	www.plantcell.org /cgi/content/full/14/1/47 (5282 words)

	ASPB - Education - GRAVITROPISM - Chapter 8
		Gravitropism (sometimes called geotropism in older texts) is a key regulatory process in plants to insure that roots grow down and shoots grow up in developing seedlings.
		As the student should find, the orientation of seeds in the soil is not important because as the radicle and shoot emerge from the seed their growth is regulated through the action of hormones to cause each organ to grow in the proper direction.
		The basic mechanism that results in gravitropism is still not resolved.
	www.aspb.org /education/lab_gravitro.cfm (855 words)

	Gravitropism: Encyclopedia topic (Site not responding. Last check: 2007-10-08)
		Gravitropism (or geotropism) is a turning or growth movement by a plant in response to gravity (gravity: A solemn and dignified feeling).
		When laid onto its side, the growing parts of the stem (stem: The tube of a tobacco pipe) begin to display negative gravitropism, bending (biologists say, turning; see tropism (tropism: An involuntary orienting response; positive or negative reaction to a stimulus source)) upwards.
		Herbaceous (non-woody) stems are capable of a small degree of actual bending, but most of the redirected movement occurs as a consequence of root or stem growth in a new direction.
	www.absoluteastronomy.com /reference/gravitropism (705 words)

	John Z. Kiss - Department of Botany - Miami University
		Gravitropism of inflorescence stems in starch- deficient mutants of Arabidopsis.
		Gravitropism of hypocotyls of wild-type and starch-deficient Arabidopsis seedlings in spaceflight studies.
		Gravitropism in roots of intermediate-starch mutants of Arabidopsis.
	www.cas.muohio.edu /botany/bot/jzk.html (733 words)

	[No title] (Site not responding. Last check: 2007-10-08)
		These severe defects in gravitropism appear to be restricted to the root, as the hypocotyl in all three eirl mutant strains tested, still reorients when germinated in the dark.
		Gravitropism, the curvature of the root in response to gravity, results from greater elongation of the upper side of the root than the lower side.
		This distribution is consistent with a model that proposes an inhibitory role for auxin in the regulation of root cell elongation and differential inhibition as the basis for gravitropism.
	www.wipo.int /cgi-pct/guest/getbykey5?KEY=99/63092.000406&ELEMENT_SET=DECL (10139 words)

	Richard D Firn - Tropisms
		Gravitropism is one of the fundamental unique physiological processes of plants and despite intensive study for 150 years it is very poorly understood.
		Good models of gravitropism must be able to account for all gravitropic behaviour not just the extremes.
		Plant organs that show differential flank elongation as part of the process of becoming curved during gravitropism or phototropism often show a reversed phase of differential flank elongation to straighten the organ again.
	www-users.york.ac.uk /~drf1/rdf_tr1.htm (664 words)

	Plant Physiology Online: Root Gravitropism
		Although this kind of evidence is consistent with the classical model of root gravitropism, it is becoming clear from detailed studies of gravitropic curvature that the classical model is over-simplified.
		We are interested in determining the relationship between the two gravitropic motor systems (DEZ and CEZ), the relationship of these motors to the two phases of the curvature response (the rapid Phase 1 and the slower Phase 2), and the relationship of the two gravity sensors to these components.
		It will be especially exciting to begin characterizing the wide variety of root gravitropism mutants (mutants with impaired ability to detect or respond to gravity) to determine the specific nature of their gravitropic lesions.
	www.plantphys.net /article.php?ch=19&id=286 (2271 words)

	JohnS2.html
		A gravitropism is a growth response in response to gravity.
		Roots have positive gravitropism, that is, they grow towards the direction that gravity is moving (i.e.
		When the root is growing parallel to gravity, there is no more "upper" and "lower" side, and therefore Ca+ and IAA are not accumulated in the "lower" side, and therefore the roots grow straight.
	www2.mcdaniel.edu /Biology/botanyweb/JohnS2.html (2011 words)

	Plant Physiology
		The mechanism generally requires: (1) an amplification of the signal; and (2) the plant must be in a physiological state to be able to respond to the stimulus.
		The evidence for this conclusion is: (a) Presentation time - there is a correlation between the rate of amyloplast sedimentation and presentation time; and (b) GA or kinetin treatment at elevated temperature (35 C), which causes starch to disappear in the roots of cress seedlings, abolishes the gravitational response.
		Recovery of gravitropism is correlated with the reappearance of amyloplasts.
	employees.csbsju.edu /ssaupe/biol327/Lecture/positioning.htm (2403 words)

	AGAINST GRAVITROPISM
		"Gravitropism" means growth in response to gravity [1].
		I use the term gravitropism in art beyond its biological origin, to underscore the fact that gravity plays a fundamental role in the forms and events we are able to create on Earth, and that forms and events created in zero gravity to be experienced in the same environment might be radically different.
		I first wrote about gravitropic forms and events in 1987, while creating and articulating the theory of a new poetic language produced out of light, with protean linguistic events floating and changing in space, freed from material and gravitational constraints.
	www.ekac.org /levitation.html (3908 words)

	Chapter 38: Control of Plant Growth and Responses (Site not responding. Last check: 2007-10-08)
		Gravitropism is response to earth's gravity; roots demonstrate positive gravitropism (Fig.
		Auxin is also involved in gravitropism, apical dominance, and root and seed development.
		Auxin-controlled cell elongation is involved in gravitropism and phototropism.
	www.sirinet.net /~jgjohnso/apbio38.html (2077 words)

	Taskbook (Site not responding. Last check: 2007-10-08)
		Gravitropism is an important process for plant growth and development.
		If/when a gravitropic defect is found, we will collaborate with other investigators to analyze the effect of these mutations on amyloplast sedimentation, the visco-elastic properties of the statocytes, the gravity-induced relocalization of auxin efflux carriers in the root tip, and cytoplasmic alkalinization of the statocytes early after gravistimulation.
		Furthermore, the new proteomic approaches that are being developed as a part of this project are likely to be very useful in the study of multiple developmental processes and responses to environmental stimuli in plants.
	taskbook.nasaprs.com /publication/index.cfm?action=public_query_taskbook_content&TASKID=2073 (809 words)

	Auxin Transport and Root Gravitropism
		One of the interests of the Muday laboratory is the role of auxin transport in plant gravitropism.
		The gravitropic bending of roots has been suggested to be mediated by change in the normal polar transport of auxin leading to lateral movement and the accumulation of auxin on the lower side of the root.
		We are also examining the role of the gaseous plant hormone, ethylene, in regulation of auxin transport and gravitropic bending.
	www.wfu.edu /academics/biology/faculty/muday/gravity.htm (477 words)

	Poff, K; Faculty Plant Biology Department at Michigan State Unversity (Site not responding. Last check: 2007-10-08)
		Our approach is to define the physiological processes, to isolate mutants with alterations in the sensory responses, to characterize these mutants physiologically, biophysically and genetically, to use particularly interesting mutants as material from which we can clone the genes of interest, and to use the genes to identify the corresponding proteins.
		By analyzing gravitropism and phototropism of a number of mutants we have shown that we can alter phototropism, leaving gravitropism normal; we can alter gravitropism, leaving phototropism normal; or we can simultaneously alter phototropism and gravitropism.
		This clear evidence for the relationship between gravitropism and phototropism could have been obtained only through a genetic approach.
	www.plantbiology.msu.edu /poff.shtml (481 words)

	Interaction of Root Gravitropism and Phototropism in Arabidopsis Wild-Type and Starchless Mutants -- Vitha et al. 122 ...
		Interaction of Root Gravitropism and Phototropism in Arabidopsis Wild-Type and Starchless Mutants -- Vitha et al.
		Root gravitropism in wild-type Arabidopsis and in two starchless mutants, pgm1-1 and adg1-1, was evaluated as a function of
		The gravitropic setpoint angle of dark-grown rye seedlings and the role of ethylene
	www.plantphysiol.org /cgi/content/abstract/122/2/453 (438 words)

	The power of chemical genomics to study the link between endomembrane system components and the gravitropic response -- ...
		Quantification of the Inhibition of the Gravitropic Response.
		The chemical library was screened in a 24-well format, and seedlings were scored for gravitropic response after reorientation.
		in the shoot gravitropic response have lesions in genes encoding
	www.pnas.org /cgi/content/full/102/13/4902 (4441 words)

	Nat' Academies Press, A Strategy for Research in Space Biology and Medicine into the Next Century (1998)
		Gravitropism in single cells might best be concentrated on the Chara rhizoid and the Ceratodon protonema systems.
		The power of genetics to dissect the steps in gravitropism is immense, and the information that could be obtained by sequencing genes directly involved in this process could lead to an understanding of how the pieces fit together.
		Studies of gravitropism must make use of the most advanced techniques available, including extensive use of genetics and transgenic plants.
	www.nap.edu /openbook/0309060478/html/59.html (745 words)

	Growth Substances
		If a plant part bends down, it is positive gravitropism (A2); if it bends up it is negative gravitropism (A3).
		Gravitropism is due to the movement of an auxin to the lower surface of the shoot where it stimulates cell division and causes the shoot to bend upwards.
		In roots, a growth inhibitor, possibly auxin or abscissic acid moves to the lower surface of the root where it actually inhibits root cell elongation.
	www.library.wisc.edu /libraries/Biology/BotanyDepartmentTeachingCollection/web-lessons/Physiology/External_factors.html (713 words)

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