On light and life Physics of chloroplast motion and bioluminescence

This thesis, "On Light and Life – Physical principles of chloroplast motion and bioluminescence",
investigates the physics of adaptive responses in biological systems in relation to light.
Focusing on the absorption of light in photosynthetic organisms - such as the aquatic plant Elodea densa - we reveal that intracellular rearrangements via chloroplast motion not only alters leaf optics for enhanced light sensitivity or photo-avoidance but also exhibits glass-like collective states under dim light. Through theoretical modeling and disk-packing simulations, we show that plant cell geometry is optimized for chloroplast arrangement, enabling dynamic transitions between absorptive and light-avoidant states.
The study is extended to the marine dinoflagellate Pyrocystis lunula, which adapts to light through contraction of a reticulated chloroplast network. This motion, facilitated by a structure reminiscent of metamaterials, acts as a temporal low-pass filter to environmental light changes, selectively responding to persistent stimuli. Despite evolutionary differences, both organisms employ chloroplast mobility for light adaptation, revealing a convergent physical strategy.
Shifting the focus to the generation of light, we study and analyze mechanically induced bioluminescence in P. Lunula by refining biophysical models of mechanosensation and light production and applying those to complex situations like wave-impact scenarios. Together, these studies uncover the interplay of intracellular organization, geometry, and dynamics in adaptation and survival.
This interdisciplinary work contributes novel insights to biological physics, particularly in active matter, organelle dynamics, and bio-inspired materials, and establishes chloroplast motion and bioluminescence as central topics to investigate how mechanics and interactions with light are coupled in biological systems.