A clinostat is a device which uses rotation to negate the effects of gravitational pull on plant growth (

gravitropism Gravitropism (also known as geotropism) is a coordinated process of differential growth by a plant in response to gravity pulling on it. It also occurs in fungi. Gravity can be either "artificial gravity" or natural gravity. It is a general featu ...

) and development ( gravimorphism). It has also been used to study the effects of

microgravity The term micro-g environment (also μg, often referred to by the term microgravity) is more or less synonymous with the terms '' weightlessness'' and ''zero-g'', but emphasising that g-forces are never exactly zero—just very small (on the ...

cell culture Cell culture or tissue culture is the process by which cells are grown under controlled conditions, generally outside of their natural environment. The term "tissue culture" was coined by American pathologist Montrose Thomas Burrows. This t ...

s, animal

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

s and

spider web A spider web, spiderweb, spider's web, or cobweb (from the archaic word '' coppe'', meaning "spider") is a structure created by a spider out of proteinaceous spider silk extruded from its spinnerets, generally meant to catch its prey. Spi ...

Description

A single axis (or horizontal) clinostat consists of a disc attached to a motor. They were originally

clockwork Clockwork refers to the inner workings of either mechanical devices called clocks and watches (where it is also called the movement) or other mechanisms that work similarly, using a series of gears driven by a spring or weight. A clockwork mec ...

but nowadays an

electric motor An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding 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 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 force In Newtonian mechanics, the centrifugal force is an inertial force (also called a "fictitious" or "pseudo" force) that appears to act on all objects when viewed in a rotating frame of reference. It is directed away from an axis which is parallel ...

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 and 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 machine 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 machine (FFM). Small samples (such as cell suspensions) are allowed to

free fall In Newtonian physics, free fall is any motion of a body where gravity is the only force acting upon it. In the context of general relativity, where gravitation is reduced to a space-time curvature, a body in free fall has no force acting on i ...

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

ethylene Ethylene ( IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene ...

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 Sachs, 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.F.C. Newcombe (1904) Limitations of the klinostat as an instrument for scientific research, Science 20, pp. 376–379.

References

Citations

External links

* Clinostat Page: A web site dedicated to space biology studies on Eart
''The Clinopage''
* Gravity experimentation websit

;Patents Cell culture (Class 435/297.400) * {{US patent, 5104802, Rhodes, Percy H. (Huntsville, AL), Miller, Teresa Y. (Falkville, AL), Snyder, Robert S. (Huntsville, AL), "'' Hollow fiber clinostat for simulating microgravity in cell culture''" Gravitational instruments Laboratory equipment