Collective dynamics in photoadaptation
Plants are more mobile than one would guess. The plant in your living room undergoes significant macroscopic motion during the course of the day and moves its leaves towards the sun. This mechanism is called heliotropism. Plants can also grow towards light (phototropism), or always find the way “up” even if light is absent (gravitotropism). While many of these dynamics have been already studied by Charles Darwin in the 19th century, their cellular mechanisms often remained elusive for decades.
It has been known since a similar time as Darwin worked on Plants, that chloroplasts, the circular photosynthetic organelles inside leafs can actively move towards or away from light, depending on the intensity.
If the light intensity is favorable they autonomously sense and move towards the light spot. However, if the intensity is strong and might harm them, they run away from the bright light and search for a more shadowy spot.
Collectively, they re-arrange in a single layer under dim light conditions to soak up as much light as possible.
This layer, however, is disordered and occasionally the randomly moving chloroplasts jump in their position. A feature normally found in glasses. The transition away from from this supercooled state, i.e. a “melting” process can be observed as soon as the intensity of the light hitting the leaf is increased.
More can be read in various news outlets: Scientific American , Phys Org
Publication in PNAS.
Authors: Nico Schramma, Cintia Perugachi Israels, Maziyar Jalaal (Fluidlab.nl)