Clinostat
Encyclopedia
A clinostat is a device which uses rotation to negate the effects of gravitational pull on plant growth (gravitropism
) and development (gravimorphism). It has also been used to study the effects of microgravity on cell culture
s and animal embryo
s.
but nowadays an electric motor
is used. The disc is held vertically and the motor rotates it slowly at rates in the order of one revolution per minute. A plant is attached to the disc so that it is held horizontally. The slow rotation means that the plant experiences a gravitational pull that is averaged over 360 degrees, thus approximating a weightless
environment. Clinostats have also been used to cancel out effects of sunlight and other stimuli besides gravity. This type of clinostat must be exactly horizontal to simulate absence of gravity. If the clinostat is at an angle from horizontal, a net gravity vector is perceived, the magnitude of which depends on the angle. This can be used to simulate lunar gravity (ca. 1/6 g) which requires an angle from the horizontal of ca. 10 deg., i.e. sin−1(1/6).
A plant only reacts to gravity if the gravistimulation is maintained for longer than a critical amount of time, called the minimal presentation time (MPT). For many plant organs the MPT lies somewhere between 10 and 200 seconds, and therefore a clinostat should rotate on a comparable timescale in order to avoid a gravitropic response. However, presentation time is cumulative, and if a clinostat's rotation is repeatedly stopped at a single position, even for periods as short as 0.5 s, a gravitropic response can result. The presentation time for animals is one or two orders of magnitude faster than this, thus precluding the use of the slow rotation clinostat for most animal studies. However the fast rotation clinostat can be, and is, used for the study of animal cell cultures and embryos.
, who built a clockwork-powered machine. However a similar concept had been pioneered as early as 1703 by Denis Dodart
. The first electric-powered clinostat (1897) was made by Newcombe.
Patents
Cell culture (Class 435/297.400)
Gravitropism
Gravitropism is a turning or growth movement by a plant or fungus in response to gravity. Charles Darwin was one of the first to scientifically document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull and stems...
) and development (gravimorphism). It has also been used to study the effects of microgravity on cell culture
Cell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...
s and animal embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s.
Description
A single axis (or horizontal) clinostat consists of a disc attached to a motor. They were originally clockworkClockwork
A clockwork is the inner workings of either a mechanical clock or a device that operates in a similar fashion. Specifically, the term refers to a mechanical device utilizing a complex series of gears....
but nowadays an electric motor
Electric motor
An electric motor converts electrical energy into mechanical energy.Most electric motors operate through the interaction of magnetic fields and current-carrying conductors to generate force...
is used. The disc is held vertically and the motor rotates it slowly at rates in the order of one revolution per minute. A plant is attached to the disc so that it is held horizontally. The slow rotation means that the plant experiences a gravitational pull that is averaged over 360 degrees, thus approximating a weightless
Weightlessness
Weightlessness is the condition that exists for an object or person when they experience little or no acceleration except the acceleration that defines their inertial trajectory, or the trajectory of pure free-fall...
environment. Clinostats have also been used to cancel out effects of sunlight and other stimuli besides gravity. This type of clinostat must be exactly horizontal to simulate absence of gravity. If the clinostat is at an angle from horizontal, a net gravity vector is perceived, the magnitude of which depends on the angle. This can be used to simulate lunar gravity (ca. 1/6 g) which requires an angle from the horizontal of ca. 10 deg., i.e. sin−1(1/6).
A plant only reacts to gravity if the gravistimulation is maintained for longer than a critical amount of time, called the minimal presentation time (MPT). For many plant organs the MPT lies somewhere between 10 and 200 seconds, and therefore a clinostat should rotate on a comparable timescale in order to avoid a gravitropic response. However, presentation time is cumulative, and if a clinostat's rotation is repeatedly stopped at a single position, even for periods as short as 0.5 s, a gravitropic response can result. The presentation time for animals is one or two orders of magnitude faster than this, thus precluding the use of the slow rotation clinostat for most animal studies. However the fast rotation clinostat can be, and is, used for the study of animal cell cultures and embryos.
Types and application
- The usual type of clinostat turns slowly to avoid centrifugal effects and this is called the "slow rotation clinostat". There has been debate as to the most suitable speed of rotation: if it is too slow the plant has time to begin physiological responses to gravity; if it is too fast, centrifugal forceCentrifugal forceCentrifugal force can generally be any force directed outward relative to some origin. More particularly, in classical mechanics, the centrifugal force is an outward force which arises when describing the motion of objects in a rotating reference frame...
s and mechanical strains introduce artifacts. The optimal rotational speed has been investigated by comparison to 'true' responses to microgravity as seen in space-grown plants, and determined to be between 0.3 and 3 rpm for most plant systems.
- The fast rotating clinostat (generally turning at between 30 to 150 rpm) can only be used for small samples (cell cultures in vials a few mm in diameter) typically in liquid media. Under these conditions excessive centrifugal effects, which precludes its use on larger samples, are avoided.
- A single-axis clinostat only produces the effect of weightlessness along its axis of rotation. A 3D or two-axis clinostat (generally called a random positioning machineRandom positioning machineA random positioning machine, or RPM, rotates biological samples along two independent axes to change their orientation in space in complex ways and so eliminate the effect of gravity .-Description:...
or RPM), can average gravitational pull over all directions. These machines often consist of two frames, one positioned inside the other, each rotating independently.
- An alternative to the clinostat for simulating microgravity is the free fall machineFree fall machineThe free fall machine is designed to permit the development of small biological sample such as cell cultures without the effect of gravity under free fall conditions.-Description:...
(FFM). Small samples (such as cell suspensions) are allowed to free fallFree fallFree fall is any motion of a body where gravity is the only force acting upon it, at least initially. These conditions produce an inertial trajectory so long as gravity remains the only force. Since this definition does not specify velocity, it also applies to objects initially moving upward...
under gravity for about a metre, with the period of free fall lasting just under a second. They are then pushed back to the top of the apparatus by a briefly applied large force (c. 20 g for 20 ms - the "bounce"), and allowed to fall again, and so on. The principle of the machine is that most of the time is spent in zero g free fall. The periods spent under high g are assumed to be too short to be detected by the physiological mechanism of the biological samples, which consequently only perceive the time spent in free fall.
Problems associated with the use of the horizontal clinostat
A number of problems have been pointed out in the use of clinostats to simulate microgravity:- gravitational effects still occur, they just have no net direction. Therefore rather than simulating microgravity they are best thought of as inducing omnilateral gravistimulation
- leaves of large plants flop about as they rotate; this may cause an increase in ethyleneEthyleneEthylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
production, which may in turn cause some of the phenomena otherwise attributed to agravitropism. Other researchers have questioned this interpretation, and it has been suggested that ethylene may have a role in the gravitropic response - vibration from the motor and other motion effects may lead to artifacts
History
The clinostat was invented in 1879 by Julius von SachsJulius von Sachs
Julius von Sachs was a German botanist from Breslau, Prussian Silesia.At an early age he showed a taste for natural history, becoming acquainted with the Breslau physiologist Jan Evangelista Purkyně. In 1851 he began studying at Charles University in Prague...
, who built a clockwork-powered machine. However a similar concept had been pioneered as early as 1703 by Denis Dodart
Denis Dodart
Denis Dodart was a French physician, naturalist and botanist. Trained at the University of Paris, he gained his doctorate of medicine in 1660 and was elected to the French Academy of Sciences in 1673. In botany he is notable for his early studies of plant respiration and growth...
. The first electric-powered clinostat (1897) was made by Newcombe.
External links
- Clinostat Page: A web site dedicated to space biology studies on Earth The Clinopage
- Gravity experimentation website Clinostats
Patents
Cell culture (Class 435/297.400)
- , Rhodes, Percy H. (Huntsville, AL), Miller, Teresa Y. (Falkville, AL), Snyder, Robert S. (Huntsville, AL) , " Hollow fiber clinostat for simulating microgravity in cell culture"