Dr. Gerhard Leubner and his Department of Plant Physiology team at the Institute of Biology II at the University of Freiburg occasionally work with what could be referred to as somewhat "tired" plants. In order for plants to restrict their germination to times when optimal environmental conditions exist, many plant species have established a strategy known as dormancy. This "sleep-like" state is a kind of a physiological blockage that prevents the plants from germinating - a phenomenon characterized by complex molecular mechanisms. When it is that the radicle finally grows, it does so in a big way. The embryo is protected by two coats - the outer seed coat and the endosperm, which are layers that provide protection and food. The seedling has to break through these two coats in order to emerge. What are the underlying mechanical processes? What happens at the physiological level? "Many of these questions can be answered by carrying out experiments on the most important plant model organism of recent years," said Leubner referring to Arabidopsis thaliana or thale cress. "But it cannot be used to answer all the questions that arise - far from it."

The two green relatives, therefore, complement each other well in experiments: the strengths of the one compensate the weaknesses of the other and vice versa. Leubner and his team are investigating the physiological processes that initiate and regulate the germination process, including the process that leads to the radicle breaking through the inner coat (i.e. endosperm). This is made possible since the endosperm starts to weaken during the germination process, initiated by the enzymes that degrade the cell wall of the enveloping tissue. The scientists use molecular biology and genetics methods in order to identify the genes that are involved in this process, in both Arabidopsis and Lepidium. The latter can also be easily genetically modified using Agrobacterium tumefaciens. The researchers use a biomechanical apparatus to find out what happens after the endosperm weakens. Puncture-force measurements enable them to determine the force required by the radicle to protrude through the endosperm. Garden cress is excellently suited to this type of experiment due to the size of its seeds.