Thresholds for Georesponse to Acceleration in Gravity-Compensated <i>Avena</i> Seedlings

Shen-Miller, J.; Hinchman, R.R.; Gordon, Solon A.

doi:10.1104/pp.43.3.338

Cited by 86 publications

(32 citation statements)

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“…45 Five Hertz corresponds to 300 rpm, a velocity that would exceed the threshold centrifugal forces (<0.0005 g, reviewed in ref. [33][34][35] for the thickness of a root (radius ~0.2 mm), and even for a typical single cell (~10 μm diameter). However, stronger curvature after faster rotation (e.g., 5 rpm) suggests that rotation affects the extent of curvature; the radius of our experimental setup (20 mm) was below the threshold of centrifugal forces (<0.0005 g).…”

Section: Discussionmentioning

confidence: 99%

“…27 Gravity compensation by clinorotation can be used to distinguish stimulus and response processes because it is possible to separate a pulse of unilateral gravistimulation (angular reorientation) from clinorotation, i.e., gravity-compensated, but omnilateral mechanostimulation. This approach has been used for the determination of the minimal (presentation) time required remaining below the threshold level of gravisensitivity (10 -3 g equivalents [33][34][35] ) as a result of centrifugal forces. The results indicate a pronounced effect of the direction of clinorotation on response to but not memory of the stimulus.…”

Section: Introductionmentioning

confidence: 99%

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Effects of mechanostimulation on gravitropism and signal persistence in flax roots

John

Hasenstein²

2011

Plant Signaling & Behavior

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of mechanostimulation on gravitropism and signal persistence in flax roots

John

Hasenstein²

2011

Plant Signaling & Behavior

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“…These display on the same clinostat centrifuge an approximate threshold of about 10 −3 g. The gravitropic sensitivity of Phycomyces is about 10 to 200 times smaller than that of Avena coleoptiles and 3 to 4 orders of magnitude smaller than that of Avena roots [12]. These huge differences can be explained by the fact that the weight of all crystals in the growing zone corresponds to that of only a single amyloplast in plants.…”

Section: Introductionmentioning

confidence: 96%

Gravireception in <i>Phycomyces</i>: Threshold Determination on the Sounding Rocket TEXUS 50

Schmidt¹

2015

JMP

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Under parabolic flight conditions microgravity is not lower than 3 to 5 times 10 −2 g. In contrast to parabolic flights, sounding rocket flights are virtually vibrational-free allowing microgravity as low as 10 −5 g. Thus, a rotating platform serving as centrifuge allows the precise generation of gravitational forces ranging from 5 to 100 mg (not possible during parabolic flights). On this basis we determined the threshold 1 for optical reflection/absorption changes in Phycomyces to be lower than 25 × 10 −3 g. This compares well with the threshold determination of gravitropism in Phycomyces on a clinostat centrifuge. Kinetics of gravity-induced absorption changes and gravity as generated by the on-board centrifuge do not coincide but show a distinctive hysteresis with a latency of 4 s (75 mg-ramp, pull-up).Keywords MDWS (Micro-Dual Wavelength Spectrophotometer), Δ GIAC (Differential Gravity-Induced Absorption Change), Phycomyces blakesleeanus, Sporangiophore, Micro-and Hypergravity, Texus 50, Sounding Rocket, Gravireception 1 The terminus "threshold" is adopted (i) from the biophysical theory of nerve signal propagation and (ii) from the physical theory of field-effect transistors (FETs). Both thresholds are typical all or none reactions; i.e. ion respectively electrical conductivity changes abruptly only if a well defined voltage, the "threshold voltage" is applied. In the theory of nerve conductivity the membrane potential must be depolarized to a precise extend in order to initiate an action potential. The threshold voltage of a field-effect transistor is the minimum gate-to-source voltage differential that is needed to create a conducting path between the source and drain terminals (e.g. representing a switch). Threshold potentials are necessary in order to regulate and propagate signals in both the central nervous system and the peripheral nervous system. However, so far it is common custom in plant physiology also to speak of "threshold of gravitropism" even if the questioned reaction is decreasing monotonously to zero upon decreasing gravi-stimuli and does not represent an all or none reaction. The "threshold" is the smallest stimulus where a response is observed. It depends on the sensitivity of the measuring set-up.

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“…(Such a relationship might prove difficult to quantify, since the amount of geostimulation necessary to cause a plant response is apparently not well defined [5,9,10,12,15,17,18,21,[23][24][25][26][27] and further seems to decrease with increasing rate of clinostat rotation [23,26,27]. )…”

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confidence: 99%

The Physical Basis of Gravity Stimulus Nullification by Clinostat Rotation

Dedolph

Dipert

1971

Plant Physiol.

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The question of how rotation on a horizontal axis clinostat removes plants from the influence of the gravitational stimulus is answered. It is shown that appropriate horizontal axis clinostat rotation restricts the fall of intracellular particles to a quasi-circular path such that the position of the particle remains virtually stationary within cells. The displacement of the path of fall, due to centrifugal force, is then considered, and a method of determining the optimal rotation rate is developed from physical principles. This method selects the rotation rate which minimizes the volume of cytoplasm through which particles pass under the joint influence of centrifugal and gravitational forces. With the recognition that single axis clinostats are ineffective with large plants or for long experiments, a new type of clinostat is proposed on which intracellular conditions can be rendered virtually identical to those of plants in satellite free fall regardless of plant size or duration of experiment.It is shown that most low gravity biological responses can be studied using clinostats with only occasional satellite free fall experiments for verification. It is further inferred that most of these responses can be effectively and economically studied by computer simulation. The existence of a lower as well as an upper limit for the effective rate of horizontal clinostat rotation was also recognized. If plants were rotated too slowly, they tended to show curvature in response to the successive stimuli imparted during rotation. It was concluded that a rotation rate of 1 revolution in four times the latency period (the period of stimulation required to produce curvature in a plant at rest) or for some cases in twice this period produced no curvature. Ultimately a revolution rate of 2 revolutions per hour was recommended as minimal, based on the reasoning that with latency periods as short as 15 min, this rate did not expose a plant to more than 7.5 min of stimulation in any given quadrant of rotation.This now historic reference concluded with a discussion of the appropriate manner of attaching plants to a clinostat and suggested that attachment should be such that the longitudinal axis of the plant should be normal (perpendicular) to the horizontal rotational axis of the clinostat.These empirically derived tenets set forth so long ago state concisely and lucidly the problem facing any worker employing the clinostat as a research instrument. Over the ensuing 66 years, discussions concerning the conditions of clinostat rotation necessary to eliminate the unidirectional stimulus of gravity have appeared (9,17,18,22) and have generally substantiated these early observations.In this manuscript, the mechanism by which horizontal-axis clinostats nullify the geotropic stimulus is explained, and the effect of clinostat-generated, centrifugal force is re-examined.

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Thresholds for Georesponse to Acceleration in Gravity-Compensated Avena Seedlings

Cited by 86 publications

References 10 publications

Effects of mechanostimulation on gravitropism and signal persistence in flax roots

Effects of mechanostimulation on gravitropism and signal persistence in flax roots

Gravireception in <i>Phycomyces</i>: Threshold Determination on the Sounding Rocket TEXUS 50

The Physical Basis of Gravity Stimulus Nullification by Clinostat Rotation

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Thresholds for Georesponse to Acceleration in Gravity-Compensated Avena Seedlings

Cited by 86 publications

References 10 publications

Effects of mechanostimulation on gravitropism and signal persistence in flax roots

Effects of mechanostimulation on gravitropism and signal persistence in flax roots

Gravireception in &lt;i&gt;Phycomyces&lt;/i&gt;: Threshold Determination on the Sounding Rocket TEXUS 50

The Physical Basis of Gravity Stimulus Nullification by Clinostat Rotation

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Gravireception in <i>Phycomyces</i>: Threshold Determination on the Sounding Rocket TEXUS 50