ABSTRACT
This chapter deals with circumnutation that occurs at the tips of longitudinally growing plant organs. Its parameters like amplitude, period, shape, and direction are reported to vary with plants and plant parts and at different environmental conditions. While the changes in some of these parameters are explainable, others are not. Four models—internal oscillator model, external gravitropic overshoot model, two-oscillator model, and growth-affected symplastic model—have been so far suggested to explain this phenomenon. Important components of all these models seem to be involved in this process. Several cellular changes are associated with circumnutation and these are explained. Circumnutation also appears to be present in woody adult plants. Mention has also been made on the genes associated with circumnutation. The importance of circumnutation to the plant is also discussed.
