Artistic seed dispersion in plants
A team of German researchers has found that many plants disperse their seeds in an almost artistic fashion. This discovery was made by researchers from the Max Planck Institute of Colloids and Interfaces in Potsdam and the Technische Universität Dresden following a thorough investigation into plants' opening mechanism. Writing in the journal Nature Communications, the team explains how when the seed capsules of plants like the ice plant Delosperma nakurense are moistened by rain, they unfold lids over the seed compartments much like a piece of movable origami. The lids open up because the honeycomb-structured cells on the inside them absorb water and change their structure. This process means that the plant, which grows in very dry regions, can ensure its seeds have a good chance of opening. The researchers hope to use this model to develop materials that move when they become wet or when their temperature changes. The research team has discovered that the lids of the seed capsules unfold on a kind of hinge when they are wet, and then close again once they dry. This also changes the curvature of the lids: the valves tightly seal the seed compartments in dry conditions. The curvature also prevents a seal opening accidentally. 'This is in fact a coordinated folding mechanism in two directions, which we know from movable origami,' explains Matthew Harrington, lead researcher on the study. The five lids of the seed capsule therefore become deformed because of their refined structure and a clever combination of the properties of various biological materials. The lids have a triangular shape; in its opened state, the seed capsule resembles a five-pointed star. They have a highly swellable tissue on the side which in the closed state points downwards, and in the open state upwards. The tissue is split into two halves and runs on the open lids - thus when the capsule is wet - from inside to outside. The two halves then close to a narrow ridge. In dry conditions, a split separates the two halves of the tissue. In the dry state, there are the partition walls of the five seed compartments in these splits, meaning the compartments are tightly sealed. When the lid opens, it deforms particularly where it is attached to the capsule, acting much like a hinge. But the team only worked out how the seal opens when they looked closely at the swellable tissue's structure. This consists of upward-opening, more or less hexagonal cells that form a honeycomb structure. These research findings also have implications for future projects across a number of different areas. 'The mechanism is interesting for technical applications because the energy for the directed movement is already stored in the material,' says Peter Fratzl. The team will now look at how they can apply this knowledge for use in biomedicine or architecture. The principle can also be transferred to materials that expand or contract in very different ways when the temperature changes: for example, an awning unfolding by itself over the patio when the sun becomes uncomfortably hot.For more information, please visit:Max Planck Institute of Colloids and Interfaces:http://www.mpikg.mpg.de/english/cont_issues/news/index.php
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