Deterministic Non-linear Dynamics in Phycomyces Sporangiophores

The growth rate of the Phycomyces sporangiophore fluctuates under constant environmental conditions. To test for deterministic non-linearity in these growth-rate fluctuations, we applied variants of several recently developed techniques. We found that wild-type sporangiophores have a significant non-linear component, whereas non-linear contributions to the growth fluctuations of a stiff (madE) mutant are less significant. This difference may be caused by the dominance of a linear 10·4 min rhythm in the mutantʹs growth rate. Previous system analysis studies, which involved stimulation by dynamically changing light intensity, identified a non-linearity near the input of the Phycomyces sensory system. Our results, which involve analysis of growth-rate fluctuations under constant environmental conditions, demonstrate the presence of deterministic non-linearity even in the absence of sensory stimulation.