Meeting Abstract

S4.3  Monday, Jan. 4  Elucidating the mechanical principles of stem movements in heliotropism RUEGGEBERG, M.**; BURGERT, I.; FRATZL, P.; Max-Planck-Institute of Colloids and Interfaces, Potsdam, Germany; Max-Planck-Institute of Colloids and Interfaces, Potsdam, Germany; Max-Planck-Institute of Colloids and Interfaces, Potsdam, Germany markus.rueggeberg@mpikg.mpg.de

Heliotropism is the movement of plant organs such as leaves or flowers in order to track the sun which can be seen in a variety of plant species. Whereas receptors and sites of light perception have been identified, the underlying mechanisms of organ movement have been well characterised for the leaves only. At the basis of leaf petioles, a specialised region consisting of motor cells, the so called pulvinus, enables the movement through (reversible) changes of cell volume due to changes in turgor pressure. However, such motor cells have not been observed in flower stems and the underlying mechanism of floral heliotropism remains to be identified. The movement is of particular interest from a biomechanical perspective. The flowers stem represents an upright beam, which is fixed on one end, whereas the other end, the flower, tracks the sun over an angle of about 180°. Thus, torsion of the plant axis might be involved as well as differential growth and/or changes in turgor pressure, enabling this particular movement. In our study, we investigate the mechanism of floral heliotropism under laboratory conditions taking the alpine plant Ranunculus alpestris as model organism. We track the 3D-movement of the stem and the flower. By combining this with a detailed analysis of the stem, especially regarding cell dimensions and orientation, we want to distinguish between irreversible movements caused by (differential) growth and reversible movements caused by turgor changes. We further intend to identify whether bending or torsional movements are involved.