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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Calcium movements and the cellular basis of gravitropism

Evidence that calcium is a significant factor in gravitropism of plants is examined, together with the regulatory mechanism that controls calcium efflux in plant cells. Calcium has been found to accumulate on the upper surface of a plant placed in a horizontal attitude, which is followed by growth to the vertical within a half-hour. It has also been determined that the upper surface of the plant simultaneously experiences a reduced growth rate, compared to the lower surface. The substance calmodulin has been identified as the calcium-binding regulatory protein most influential in the transduction process leading to gravitropism, while chlorpromazine can inhibit its effects. The calcium is transported by ATPase located in the cell membrane. A possibility that the calcium pump is regulated by a feedback mechanism involving the presence of calmodulin is discussed.

Roux, S. J.↗
NASA NTRS1983

Evidence for a Regulatory Role of Calcium in Gravitropism

Experiments conducted to determine the cellular basis of gravitropism, the phenomenon of calcium migration following gravitropic stimulation, and the preferential accumulation of calcium in cells are described. Results of autoradiographic studies of cross sections of oat, and the pryoantimony precipitation of calcium in situ are discussed. It was found that the movement of calcium during gravimetric stimulation is a redistribution of calcium from the vacuolar regions into the cells walls. This movement requires precipitation of a calcium ATPase. The control of calcium ATPase by calmodulin and whether chlorpromazine is binding to calmodulin in plants are considered.

Roux, S. J.↗
NASA NTRS1984

Inhibition of gravitropism in oat coleoptiles by calcium chelation

Some cellular event necessary for gravitropism is inhibited by EGTA without interferring with the overall growth. Calcium relieves this inhibition and demonstrates both that inhibition is reversible and was probably due to a reduction in the ability to free calcium required for one or more at the transduction steps of gravitropism. At the near neutral pH used, EGTA is charged and would not be expected to readily cross the membrane. One of its primary effects, then, is probably the bringing of free calcium in the apoplastic space exterior to the cell membranes.

Roux, S. J.↗
NASA NTRS1984

Mechanism of shoot gravitropism

A better understanding of the cellular basis of plant shoot gravitropism was sought. A critical evaluation of the role of auxin gravitropism was provided. An alternative hypothesis which links Ca(42) fluxes to the asymmetric growth that leads to gravicurvature was evaluated.

Rayle, D. L.↗
NASA NTRS1984

Gravitropism in leafy dicot stems

In an attempt to separate plant responses to mechanical stresses from responses to gravity compensation, six treatments were automated: (1) upright stationary controls; (2) horizontal clinostat; (3) intermittent clinostat (plants upright 3.3 minutes out of every 4 minutes, horizontal and rotated once in the remaining time); (4) inversion every ten minutes (plants upside down half the time); (5) inversion and immediate return to the vertical; and (6) vertical rotation. Epinasty appeared only on clinostated and on inverted plants, both subjected to gravity compensation. The mechanics of gravitropic stem bending and the effects of a unilateral application of ethephon of gravitropic bending were also investigated.

Salisbury, F. B.↗
NASA NTRS1984

Measurement of thigmomorphogenesis and gravitropism by non-intrusive computerized video image processing

A video image processing instrument, DARWIN (Digital Analyser of Resolvable Whole-pictures by Image Numeration), was developed. It was programmed to measure stem or root growth and bending, and coupled to a specially mounted video camera to be able to automatically generate growth and bending curves during gravitropism. The growth of the plant is recorded on a video casette recorder with a specially modified time lapse function. At the end of the experiment, DARWIN analyses the growth or movement and prints out bending and growth curves. This system was used to measure thigmomorphagenesis in light grown corn plants. If the plant is rubbed with an applied force load of 0.38 N., it grows faster than the unrubbed control, whereas 1.14 N. retards its growth. Image analysis shows that most of the change in the rate of growth is caused in the first hour after rubbing. When DARWIN was used to measure gravitropism in dark grown oat seedlings, it was found that the top side of the shoot contracts during the first hour of gravitational stimulus, whereas the bottom side begins to elongate after 10 to 15 minutes.

Jaffe, M. J.↗
NASA NTRS1984

Participation of ethylene in gravitropism

In shoots of many plants, of which tomato (Lycopersicon esculentum Mill.) is an example, ethylene production is substantially increased during gravitropism. As a first step toward elucidating the role of ethylene in gravitropism, detailed time courses of ethylene production in isolated hypocotyl segments and whole plants were measured for gravistimulated and upright tomato seedlings. In the first experiment, seedlings were set upright or laid horizontal and then, at 15 min intervals, sets of hypocotyls were excised and sealed into gas tight vials. A steady long term rise in ethylene production begins after 15 min gravistimulation. It is possible that this increase is a consequence of the accumulation of indoleacetic acid (IAA) in the lower tissue of the hypocotyle. In a second kind of experiment, whole seedlings were enclosed in sealed chambers and air samples were withdrawn at 5 min intervals. Stimulated seedlings produced more ethylene than controls during the first 5 min interval, but not appreciably more during the second. This suggests the possibility that the ethylene production induced during the first 5 min occurs immediately rather than after a lag, and thus much too soon to be controlled by redistribution of IAA.

Harrison, M.↗
NASA NTRS1985

Calcium and Calmodulin Localization in Gravitropically-responding Plant Organs

Antimonate staining procedures were used to detect calcium redistribution changes in corn roots. Results show that an asymmetric redistribution of Ca is induced by a gravitropic stimulus in roots as it is in shoots. Since this response occurs within 10 min, at least 5 min before any visible bending, it could play a role in the regulation of root gravitropism. Two different general approaches were used to localize calmodulin in plant tissue: radioimmunoassay of its content in tissue and in purified subcellular organelles, and immunocytochemical detection of it in roots and coleoptiles. Radioimmunoassay results indicate that calmodulin is present in large quantities in pllant cells and that it is specifically associated with mitochondria, etioplasts and nuclei. An assayed of an extract of soluble wall proteins revealed that over 1% of these proteins was calmodulin. Controls indicate that this calmodulin is not cytoplasmic in origin. A reaction product from anti-calmodulin was found mainly in the root cap cells, moderately in metazylem elements, in some cells in the stele surrounding metaxylem elements and in cortical cells.

Roux, S. J.↗
NASA NTRS1985

Mutant Peas as Probes in the Understanding of Growth and Gravitropism

One mutant of Pism sativum CREEP grows normally up to the first internode stage, and then begins to grow plagiotropically. The upper internodes bend slowly downward according to a programmed sequence which follows circumnutation of the previous internode and opening of the previous leaves, but preceeds expansion of the previous leaves. The bending is partially inhibited by excission of the opposing stipules. The second mutant, AGEOTROPUM is gravitropically incompetant when grown etiolated, in the dark. When etiolated plants are illuminated with white light, the stems become gravitropically competant, but the roots do not. If the plants are grown in the light in particulate medium, some secondary roots, growing randomly, emerge into the air, and turn and grow downward toward moist soil. When etiolated AGEOTROPUM plants are illuminated, the shoots then become able to respond to gravity in a normal, negatively orthogravitropic manner. The response is to red light and is reversed by far red light. The mutation may involve one or more of the following: (1) release of sequestered calcium for redistribution; (2) radial transport of released calcium; or (3) net calcium flux in the upward direction.

Jaffe, M. J.↗
NASA NTRS1989

Gravitropism in plants: Hydraulics and wall growth properties of responding cells

Gravitropism is the asymmetrical alteration of plant growth in response to a change in the gravity vector, with the typical result that stems grow up and roots grow down. The gravity response is important for plants because it enables them to grow their aerial parts in a mechanically stable (upright) position and to develop their roots and leaves to make efficient use of soil nutrients and sunlight. The elucidation of gravitropic responses will tell much about how gravity exerts its morphogenetic effects on plants and how plants regulate their growth at the cellular and molecular levels.

Cosgrove, Daniel J.↗
NASA NTRS1986

Gravitropism in higher plant shoots. IV - Further studies on participation of ethylene

Various hypotheses regarding the influence of ethylene on gravitropism in higher plant shoots were experimentally tested. It was found that ethylene at 1.0 and 10.0 cu cm/cu m decreased the rate of gravitropic bending in cocklebur stems, while 0.1 cm/cu m of ethylene had little effect. Treating cocklebur plants with 1.0 mmol aminoethoxyvinylglycine (AVG, an ethylene synthesis inhibitor) delayed stem bending compared with controls, but adding 0.1 cu cm/cu m ethylene in the surrounding atmosphere partially restored the rate of bending of AVG-treated plants. Virtually all newly synthesized ethylene appeared in bottom halves of horizontal stems, where ethylene concentrations were as much as 100 times those in upright stems or in top halves of horizontal stems. Auxin applied to one side of a vertical stem caused extreme bending away from that side; gibberellic acid, kinetin, and abscisic acid were without effect.

Wheeler, Raymond M.↗
NASA NTRS2003

Microinjection--a tool to study gravitropism

Despite extensive studies on plant gravitropism this phenomenon is still poorly understood. The separation of gravity sensing, signal transduction and response is a common concept but especially the mechanism of gravisensing remains unclear. This paper focuses on microinjection as powerful tool to investigate gravisensing in plants. We describe the microinjection of magnetic beads in rhizoids of the green alga Chara and related subsequent manipulation of the gravisensing system. After injection, an external magnet can control the movement of the magnetic beads. We demonstrate successful injection of magnetic beads into rhizoids and describe a multitude of experiments that can be carried out to investigate gravitropism in Chara rhizoids. In addition to examining mechanical properties, bead microinjection is also useful for probing the function of the cytoskeleton by coating beads with drugs that interfere with the cytoskeleton. The injection of fluorescently labeled beads or probes may reveal the involvement of the cytoskeleton during gravistimulation and response in living cells. c2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

NASA Program Fundamental Space Biology↗
NASA NTRS2003

Phytochromes play a role in phototropism and gravitropism in Arabidopsis roots

Phototropism as well as gravitropism plays a role in the oriented growth of roots in flowering plants. In blue or white light, roots exhibit negative phototropism, but red light induces positive phototropism in Arabidopsis roots. Phytochrome A (phyA) and phyB mediate the positive red-light-based photoresponse in roots since single mutants (and the double phyAB mutant) were severely impaired in this response. In blue-light-based negative phototropism, phyA and phyAB (but not phyB) were inhibited in the response relative to the WT. In root gravitropism, phyB and phyAB (but not phyA) were inhibited in the response compared to the WT. The differences observed in tropistic responses were not due to growth limitations since the growth rates among all the mutants tested were not significantly different from that of the WT. Thus, our study shows that the blue-light and red-light systems interact in roots and that phytochrome plays a key role in plant development by integrating multiple environmental stimuli. c2003 COSPAR. Published by Elsevier Ltd. All rights reserved.

Non-NASA Center↗
NASA NTRS2003

Extracellular ATP inhibits root gravitropism at concentrations that inhibit polar auxin transport

Raising the level of extracellular ATP to mM concentrations similar to those found inside cells can block gravitropism of Arabidopsis roots. When plants are grown in Murashige and Skoog medium supplied with 1 mM ATP, their roots grow horizontally instead of growing straight down. Medium with 2 mM ATP induces root curling, and 3 mM ATP stimulates lateral root growth. When plants are transferred to medium containing exogenous ATP, the gravity response is reduced or in some cases completely blocked by ATP. Equivalent concentrations of ADP or inorganic phosphate have slight but usually statistically insignificant effects, suggesting the specificity of ATP in these responses. The ATP effects may be attributable to the disturbance of auxin distribution in roots by exogenously applied ATP, because extracellular ATP can alter the pattern of auxin-induced gene expression in DR5-beta-glucuronidase transgenic plants and increase the response sensitivity of plant roots to exogenously added auxin. The presence of extracellular ATP also decreases basipetal auxin transport in a dose-dependent fashion in both maize (Zea mays) and Arabidopsis roots and increases the retention of [(3)H]indole-3-acetic acid in root tips of maize. Taken together, these results suggest that the inhibitory effects of extracellular ATP on auxin distribution may happen at the level of auxin export. The potential role of the trans-plasma membrane ATP gradient in auxin export and plant root gravitropism is discussed.

Non-NASA Center↗
NASA NTRS2002

Interactions between gravitropism and phototropism in plants

To receive adequate light and nutrients for survival, plants orient stems and stem-like organs toward light and away from the gravity vector and, conversely, orient roots into the soil, away from light toward the direction of gravity. Therefore, both gravity and light can influence the differential growth of plant organs. To add to the complexity of the interactions between gravity and light, each stimulus can enhance or reduce the effectiveness of the other. On earth, the constant presence of gravity makes it difficult to determine whether plant growth and development is influenced by gravity or light alone or the combination of the two stimuli. In the past decade, our understanding of the gravity and light transduction pathways has advanced through the use of mutants in either gravitropic or phototropic responses and the use of innovative techniques that reduce the effects of one stimulus on the other. Thus, both unique and common elements in the transduction pathways of the gravitropic and phototropic responses have been isolated. This article is focused on the interactions between the light- and gravity-transduction pathways and describes methods used to separate the influences of these two environmental stimuli.

NASA Discipline Plant Biology↗
NASA NTRS2002

Root gravitropism in response to a signal originating outside of the cap

We have developed image analysis software linked to a rotating stage, allowing constraint of any user-selected region of a root at a prescribed angle during root gravitropism. This device allows the cap of a graviresponding root to reach vertical while maintaining a selected region within the elongation zone at a gravistimulated angle. Under these conditions gravitropic curvature of roots of Zea mays L. continues long after the root cap reaches vertical, indicating that a signal from outside of the cap can contribute to the curvature response.

Non-NASA Center↗
NASA NTRS1997

Interaction of light and gravitropism with nutation of hypocotyls of Arabidopsis thaliana seedlings

Etiolated seedlings of Arabidopsis thaliana nutated under conditions of physiological darkness while about ten percent of monitored individuals exhibited regular elliptical nutation, circumnutation. Pre-irradiation with red light prevented occurrence of circumnutation without having an effect on the average rate of the nutational movement. Phototropic response of seedlings to unilateral blue light appeared to be superimposed over nutation. Throughout gravitropism, some seedlings continued to exhibit nutation suggesting that these two processes are independently controlled. Based on these results, we suggest that nutation in Arabidopsis probably is not controlled by the mechanism predicted by the theory of gravitropic overshoots.

NASA Discipline Plant Biology↗
NASA NTRS1997

Cytochalasin D does not inhibit gravitropism in roots

It is generally thought that sedimenting plastids are responsible for gravity sensing in higher plants. We directly tested the model generated by the current statolith hypothesis that the gravity sensing that leads to gravitropism results from an interaction between the plastids and actin microfilaments. We find that the primary roots of rice, corn, and cress undergo normal gravitropism and growth even when exposed to cytochalasin D, a disruptor of actin microfilaments. These results indicate that an interaction between amyloplasts and the actin cytoskeleton is not critical for gravity sensing in higher plants and weaken the current statolith hypothesis.

NASA Discipline Plant Biology↗