Gravity-dependent polarity of cytoplasmic streaming inNitellopsis

Wayne, Randy; Staves, Mark P.; Leopold, A. C.

doi:10.1007/bf01322614

Cited by 80 publications

(48 citation statements)

References 45 publications

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“…While gravity could be sensed and curvature initiated by the individual plant cell (if it is capable of growth), the noise which accompanies all channel behaviour would likely ensure that gravity perception would be weak and stochastic and the response slow and variable. Wayne et al (1990) suggest that the primary reason the higher-plant graviperceptive ceils have starch-filled amyloplasts is simply to increase the density of the protoplast, i.e. to act like ballast, thus greatly refining the accuracy of graviperception.…”

Section: Discussionmentioning

confidence: 98%

“…Thus many (if not all) cells of the seedling are able to increase CaM mRNA levels in response to a gravitational stimulus and are thus gravisensitive, not just those containing amyloplasts. Wayne et al (1990) have recently suggested that graviperception in giant algal cells could be mediated by compression of the basal plasma membrane as a result of the weight of the cytoplasm. They show there is sufficient potential energy in this mechanism to open numerous stretch-activated calcium channels.…”

Section: Discussionmentioning

confidence: 99%

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The role of calmodulin in the gravitropic response of the Arabidopsis thaliana agr-3 mutant

Sinclair

Oliver

Maher

et al. 1996

Planta

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Calmodulin, a primary plant calcium receptor, is known to be intimately involved with gravitropic sensing and transduction. Using the calmodulin-binding inhibitors trifluoperazine, W7 and calmidazolium, gravitropic curvature of Arabidopsis thaliana (L.) Heynh, ecotype Landsberg, roots was separable into two phases. Phase I was detected at very low concentrations (0.01 microM) of trifluoperazine and calmidazolium, did not involve growth changes, accounted for about half the total curvature of the root and may represent the specific contribution of the cap to gravity sensing. Phase II commenced around 1.0 microM and involved inhibition of both growth and curvature. The agr-3 mutant exhibited a reduced gravitropic response and was found to lack phase I curvature, suggesting that the mutation alters either use or expression of calmodulin. The sequences of wild-type and agr-3 calmodulin (CaM-1) cDNAs, which are root specific were completely determined and found to be identical. Upon gravitropic stimulation, wild-type Arabidopsis seedlings increased calmodulin mRNA levels by threefold in 0.5 h. On the other hand, gravitropic stimulation of agr-3 decreased calmodulin mRNA accumulation. The possible basis of the two phases of curvature is discussed and it is concluded that agr-3 has a lesion located in a general gravity transmission sequence, present in many root cells, which involves calmodulin mRNA accumulation.

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Section: Discussionmentioning

confidence: 98%

Section: Discussionmentioning

confidence: 99%

The role of calmodulin in the gravitropic response of the Arabidopsis thaliana agr-3 mutant

Sinclair

Oliver

Maher

et al. 1996

Planta

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“…Most of the biophysical parameters required to accurately model the statolith dynamics have been determined to varying degrees of accuracy, such as amyloplast density (Leach and Schoch, 1961;Robinson, 1985;Wayne et al, 1990) and maize and whiteclover statolith dimensions (Moore, 1986;Smith, 1996;Smith et al, 1997). If cytoplasmic viscosity is assumed to be 5 to 20 cP (Sack et al, 1985), the elastic forces due to interaction with the cytoskeletal network (F actin ) remain to be characterized.…”

Section: Physical Simulation Of the Tethered Statolith Model Of Gravimentioning

confidence: 99%

Amyloplast Sedimentation Dynamics in Maize Columella Cells Support a New Model for the Gravity-Sensing Apparatus of Roots

et al. 2001

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Quantitative analysis of statolith sedimentation behavior was accomplished using videomicroscopy of living columella cells of corn (Zea mays) roots, which displayed no systematic cytoplasmic streaming. Following 90°rotation of the root, the statoliths moved downward along the distal wall and then spread out along the bottom with an average velocity of 1.7 m min Ϫ1 . When statolith trajectories traversed the complete width or length of the cell, they initially moved horizontally toward channel-initiation sites and then moved vertically through the channels to the lower side of the reoriented cell where they again dispersed. These statoliths exhibited a significantly lower average velocity than those sedimenting on distal-toside trajectories. In addition, although statoliths undergoing distal-to-side sedimentation began at their highest velocity and slowed monotonically as they approached the lower cell membrane, statoliths crossing the cell's central region remained slow initially and accelerated to maximum speed once they reached a channel. The statoliths accelerated sooner, and the channeling effect was less pronounced in roots treated with cytochalasin D. Parallel ultrastructural studies of high-pressure frozen-freeze-substituted columella cells suggest that the low-resistance statolith pathway in the cell periphery corresponds to the sharp interface between the endoplasmic reticulum (ER)-rich cortical and the ER-devoid central region of these cells. The central region is also shown to contain an actin-based cytoskeletal network in which the individual, straight, actin-like filaments are randomly distributed. To explain these findings as well as the results of physical simulation experiments, we have formulated a new, tensegrity-based model of gravity sensing in columella cells. This model envisages the cytoplasm as pervaded by an actin-based cytoskeletal network that is denser in the ER-devoid central region than in the ER-rich cell cortex and is linked to stretch receptors in the plasma membrane. Sedimenting statoliths are postulated to produce a directional signal by locally disrupting the network and thereby altering the balance of forces acting on the receptors in different plasma membrane regions.For nearly 100 years the dense, starch-filled amyloplasts within the columella cells of the higher plant root cap have been proposed to serve as the gravitysensing structures of the plant root gravitropic system (Haberlandt, 1900;Nemec, 1900; Darwin, 1903). The sedimentation of these amyloplasts (or statoliths) in response to gravity, and the columella cells (or statocytes) in which they are found, have repeatedly been shown to be necessary for a proper root response to gravity (

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“…Thus, it has to be concluded that amyloplast sedimentation is not the sole mechanism in graviperception. At least, there exist two hypotheses about the mass responsible for gravisensing: the model of Wayne et al [26] postulating that the entire mass of a specialized cell is able to provide a signal for compression or tension (Fig. 19.6, left).…”

Section: The Plastid-based Gravisensingmentioning

confidence: 98%

Gravistimulated Effects in Plants

Schnabl¹

2002

Astrobiology

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Plant growth and development are affected by a lot of different environmental abiotic factors such as light, temperature and water supply. Immediately upon germination another physical stimulus, gravity, strongly influences the growth of plant organs, root and shoot, in order to ensure their correct orientation in space and the survival of the young seedling. Since plants have evolved under the constant stimulus of gravity, its presence is one of the most important prerequisites for their growth and spatial orientation. Because of the importance of gravity it is astonishing that sensitivity to the gravitational vector, the mechanisms of graviperception and gravisresponse which are still partially controversially discussed, are unclear up to now. Indeed, we know that the framework of the plant body is disturbed without the permanent g-vector, its physiological balance is disrupted. But we do not know the way the gravitational force as an abiotic signal is translated into gravity-dependent phenomena and definite plant structures maintaining adaptive strategies for survival. The biological effects of gravity (studies under microgravity) would be easier understood if this abiotic factor could be reduced or minimized as other common environmental parameters can be modified in order to study their effects on plant differentiation and growth.Since we have no ways to reduce the gravity vector on our planet without inducing stress, we may only speculate on the strategies of plant adaptation mechanisms during the evolution. Leaving the original life space, the water environment, and occupying the land environment 400 million years ago, the plants have been forced to adapt to the new conditions characterized by missing convection. Thereby land-plants were affected by a force 1000 times bigger than in water. The local orientated plants had to optimize their life conditions with respect to water balance, to nutrition, to mechanical problems and to reproduction changing the typical horizontal orientated vegetative thallus into the upright orientated plant body, the cormus. This statically local orientated life way resulted in a high adaptation strategy to environmental factors (Fig. 19.1). In order to overcome mechanical problems induced by the deficiency of the convection, the collapse of the plant cormus had to be avoided by the formation of tissues, delivering special structural rigidity, such as the deposition of lignin in the secondary wall. The supply of water, minerals and nutrition materials had to be organized by the development of a system for the conduction of water and minerals from the soil via the roots in the rest of the plants (xylem) and for the transport of the products of photosynthesis from the leaves throughout the plant (phloem). The total vessels are known as the vascular bundles. Moreover, the plants had to develop suitable nutrition sources, resulting in the formation of leaves which are able to fix CO2 and to store carbohydrates. The shoot functions as the mediator between root and leaves. Other

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Gravity-dependent polarity of cytoplasmic streaming inNitellopsis

Cited by 80 publications

References 45 publications

The role of calmodulin in the gravitropic response of the Arabidopsis thaliana agr-3 mutant

The role of calmodulin in the gravitropic response of the Arabidopsis thaliana agr-3 mutant

Amyloplast Sedimentation Dynamics in Maize Columella Cells Support a New Model for the Gravity-Sensing Apparatus of Roots

Gravistimulated Effects in Plants

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