Light-Dependent Morphological Changes Can Tune Light Absorption in Iridescent Plant Chloroplasts: A Numerical Study Using Biologically Realistic Data

In higher plants and algae, chloroplasts are the organelle responsible for photosynthesis. Previous work has focused mostly on the role of the photosynthetic pigments; however, recent advances demonstrated that light interactions within chloroplasts could make use of intrinsic nanophotonic properties to manipulate light to enhance light-harvesting efficiency. We hypothesize that the documented morphological changes undergone by chloroplasts under varying light conditions can highly influence the light-harvesting properties due to nanophotonic effects. In this work, we focused on a type of specialized chloroplast known as the iridoplast, which has intrinsic photonic crystal properties such as strong reflectance and slow light effects. We studied how the photonic properties of iridoplasts are affected by light-induced dynamic changes using realistic data extracted from previous reports. The results show a reflectance red-shift from blue to green under increasing light intensity. Consequently, the light absorption enhancement induced by slow light is also red-shifted. We also showed that the photonic properties are resilient to biologically realistic levels of disorder in the structure. We extended this analysis to another photonic nanostructure-containing chloroplast, known as a bizonoplast, and found similar results, pointing toward similar properties in different plant species. We finally demonstrated that all types of chloroplasts can tune light absorption depending on light conditions. In general, our study opens the door to understanding how dynamic morphological changes in chloroplasts can affect light scattering and absorption.