Analysis of the Spadix Temperature Control Mechanism in Skunk Cabbage by Using the Proportional Integral Differential (PID) Algorithm

Abstract

We examined the applicability of feedback control with proportional integral differential (PID) action to the temperature control mechanism in the spadix, a thermogenic organ of skunk cabbage (Symplocarpus renifolius). We covered plants with a container and cooled with snow. The next day, we removed the snow and container, which resulted in a rapid temperature change, and continued to monitor the ambient and spadix temperature for several days. We found that the target temperature of the spadix at the early male phase is not constant but can be expressed by a variable value that changes linearly with the outside temperature. We found that the thermogenic state can be quantitatively described by the activation coefficient, which was higher in skunk cabbage than in lotus (another thermogenic plant). We modeled the mechanisms of the spadix temperature control; in our model, a transfer function to the spadix center from the heating portion near the surface and the outside temperature was described as a first-order lag system, and changes in the target temperature as a feedback. We found that the control was achieved by integral action. The control system returned the spadix temperature to the target value with a slight delay in response to sudden changes in the outside temperature, or gradually with little delay in response to gradual changes. We conclude that the spadix temperature changes in accordance with a variable target value.