Information, Noise and Communication: Thresholds as Controlling Elements in Development

Abstract

Organisms are dependent on the continual transmission of information both within cells and from outside them. Information is concerned with the conveyance of signals that require both a transmitter and a receiver able to decide what is sent. Accuracy in transmission is degraded by noise, and the evidence that shows noisiness in genetic circuitry is described. Reliable noise coupled with positive feedback constructs probabilistic thresholds amongst a population. In higher plants, stochastic distribution of thresholds enables quantitative variation amongst cells, tissues or plants to variable strengths of signals. It is the function of information to be communicated, but the gel structure of the cytoplasm together with the ordering by structured water might instead increase noise in transmission by interfering with the necessary movement of molecules in signal transduction. To reduce potential noise in signal transmission and transduction, it is suggested that abrupt phase transitions in microdomains of the cytoplasmic gel structure are induced by cytoplasmic calcium, amongst other signals. Plasmodesmata also contain actin gels, and communication between cells may simply be controlled by abrupt gel phase transitions. Two threshold phenomena are thus seen in plant cells important during development. The first involves noise and positive feedback; the second, gel phase transition.