Root movements: Towards an understanding through attempts to model the processes involved

Abstract

Roots have the ability to change the direction of their forward growth. Sometimes these directional changes are rapid, as in mutations, or they are slower, as in tropisms. The gravitational force is always present and roots have an efficient graviperception mechanism which enables them to initiate gravitropic movements. In trying to model and simulate the course of gravitropic root movements with a view to analyse the component processes, the following aspects of the plant's interaction with gravity have been considered: (1) The level of organization (organism, organ, cell) at which the movement process is expressed; (2) whether the gravity stimulation event is dynamic or static (i.e. whether or not physiologically significant displacements take place with respect to the gravity vector); (3) the sub-systems involved in movement and the processes which they regulate; (4) the mathematical characterization of the relevant sub-systems. A further allied topic is the nature of nutational movements and whether they are linked with gravitropic movements in some way. In considering how they can best be modelled, two types of nutational movements are proposed: stochastic nutation and circumnutation. Most, if not all, natural movements developed in response to static gravistimulation can be viewed as gravimorphisms. This applies at the levels of cell, organ and organism. However, when a system at any one of these levels experiences dynamic gravistimulation, because of its inherent homeostatic properties, it is induced to regenerate a state similar to that previously held. Thus, gravitropism is a regenerative gravimorphic process at the level of the organ.

Tree Related Subsidence of Low Rise Buildings and the Management Options

“…However, others have shown that in nature whole plant processes may have a more powerful influence on root growth and orientation than processes at the level of the individual root; (KRAMER and KOZLOWSKI, 1979). Root mutations are poorly understood, but some show an unpredictable (stochastic) pattern of tip movement (BARLOW and ZIESCHANG, 1994). Modeling of root growth using computer algorithms (FITTER et al, 1991), simulated the growth of a root system and its exploitation of the soil, calculated the relationship between its exploitation and its architectural characteristics.…”

Plagiogravitropism of maize roots

“…Plagiogravitropism of a root is usually characterized by the existence of a non-zero liminal angle from the vertical. Although gravitropic curvature is composed of a series of five events or reactions; namely, the physical perception of gravity stimulus, the transformation of physical events into physiological changes, the transmission of the gravityinduced physiological state into the growth zone, the bending process, and the establishment of the liminal angle (Barlow and Zieschang, 1994;Jackson and Barlow, 1981), the mechanisms controlling the last step, that is, how a root maintains its direction of growth deviating from the vertical, has yet to be found.…”

Hydrotropism in roots: sensing of a gradient in water potential by the root cap

“…Application of a gradient in water potential to the root cap might cause not only hydrotropic curvature but also an enhancement of nutational movement of the root. Study of sorbitol-induced hydrotropism and nutational movement may provide a clue to understanding the mechanisms involved in root movements because nutation and tropisms in roots usually interact with one another in determining the direction of root forward growth (Barlow and Zieschang 1994).…”