Light-controlled Chloroplast Network-Morphodynamics in single-celled Algae

The ability of photosynthetic organisms to convert light into biochemically available energy is the basis for most life on earth. At the same time, too much light can be detrimental for an organisms survival. Plants and algae have to constantly cope with fluctuating light. Besides biochemical and developmental mechanisms, they have evolved the ability to re-arrange their intracellular structure by collectively moving their chloroplasts - light harvesting organelles - within their cell-body to adaptively tune the overall light absorption.

We uncover that the bioluminescent dinoflagellate Pyrocystis lunula, native to dim light conditions in the ocean, can rearrange its intracellular structure efficiently by rapidly contracting a topologically complex network of chloroplasts that spans throughout the cell.

By exploiting buckling of the active network strands it exhibits mechanical deformation similar to that of meta-materials, resulting in efficient compaction within the cell wall confinement.

Ultimately, we control the cell using dynamic light stimulation, and uncover that the cell's response follows rules similar to temporal low-pass filtering - an elegant adaptation process at a single-cell level toward environmental fluctuations. Besides the physiological and ecological relevance, the light-controlled morphodynamics of the chloroplast network represents a well-controlled active matter system, manifesting a biological metamaterial.