Why does Zero-gravity increase Mitosis?
Gravity is the force of attraction exhibited by the earth on every object on the earth. This gravitational force is responsible for every object to have the tendency to fall down if there is nothing between to stop it. However, if an object develops a force by itself that can nullify the gravitational force that is pulling it, then the object can prevent itself from falling down due to gravity. This force that can be developed due to inertia is called centrifugal force. If the centrifugal force balances the gravitational force then the object will experience weightlessness. Weight is mass multiplied by gravitational force. If the gravity is nullified then weight becomes zero. Hence, this state is said to be occurring at zero gravity.
In a study conducted by Jane Shen-Miller et. al., in 1978, published in the Journal of plant physiology, it is proven that cell division and differentiation of root cells will take place when a geotropic stimulus is given to the plant root. The triggering of root cell mitosis by the gravity was found to be due to multi-hormonal effect. In another study conducted in 2007 by Jie He et al., published in the Journal Acta Astronautica, it is proven that changes or alterations in gravity or geotropic stimulus will affect the cell cycle in Physarum polycephalum. The above work shows that gravity has an influence on the mitosis of the plant cell especially the root cells. It is also found in the above studies that root cap signals to stop or inhibit the growth of other root meristematic cells in the presence of geotropic stimulus. Root cap will be active in a growth by itself more than the other root cells when triggered by gravity.
Hence, in the absence of gravitational force or in the presence of zero-gravity, the root cap cells signal the stimulation of the cell division in the cortical regions or the other meristematic regions. When the root cap signals are received then the root lateral cells undergo mitosis and give rise to secondary roots. Therefore it is observed that gravity stimulates the root cap growth while zero-gravity triggers the mitosis of other root cells.