The pollen tube: a soft shell with a hard core

Plant cell expansion is controlled by a fine-tuned balance between intracellular turgor pressure, cell wall loosening and cell wall biosynthesis. To understand these processes, it is important to gain in-depth knowledge of cell wall mechanics. Pollen tubes are tip-growing cells that provide an ideal system to study mechanical properties at the single cell level. With the available approaches it was not easy to measure important mechanical parameters of pollen tubes, such as the elasticity of the cell wall. We used a cellular force microscope (CFM) to measure the apparent stiffness of lily pollen tubes. In combination with a mechanical model based on the finite element method (FEM), this allowed us to calculate turgor pressure and cell wall elasticity, which we found to be around 0.3 MPa and 20–90 MPa, respectively. Furthermore, and in contrast to previous reports, we showed that the difference in stiffness between the pollen tube tip and the shank can be explained solely by the geometry of the pollen tube. CFM, in combination with an FEM-based model, provides a powerful method to evaluate important mechanical parameters of single, growing cells. Our findings indicate that the cell wall of growing pollen tubes has mechanical properties similar to rubber. This suggests that a fully turgid pollen tube is a relatively stiff, yet flexible cell that can react very quickly to obstacles or attractants by adjusting the direction of growth on its way through the female transmitting tissue.

Multigrade teaching in primary education as a promising pedagogy for teacher education in Austria and Finland

This chapter focuses on teaching practices used in multigrade classes and the importance of them being incorporated in teacher education as promising pedagogies for future use. Multigrade classes - defined as classes in which two or more grades are taught together - are common worldwide. Hence, there is a need for teacher candidates to become familiar with how to teach in split grade classrooms. However, research on multigrade teaching as well as its development in teacher education studies has been neglected, even though multigrade teachers need special skills to organize instruction in their heterogeneous classrooms. We argue that in successful multigrade teaching practices, the heterogeneity of students is taken into account and cultivated. Based on content analysis of teacher interviews conducted in Austrian and Finnish primary schools, we recommend teaching practices such as spiral curricula, working plans, and peer learning as promising teacher education pedagogies for future multigrade class teaching. We also suggest that the professional skills required in high-quality teaching practices in multigrade teaching should be further studied by researchers and educators.