A shade-dwelling plant has adapted to the extremely low-light conditions of its environment by using its iridescent blue leaves to manipulate quantum mechanics and enhance photosynthesis, reports a paper published online this week in Nature Plants.
Chloroplasts harvest sunlight and convert it into chemical energy for the plant, with light initially absorbed by membranes - called thylakoids - that assemble into large, variably sized stacks. Begonia pavonina, which is found under the thick canopies of tropical forests in Malaysia, has iridescent blue leaves due to unusual chloroplasts, known as iridoplasts, in its surface layers.
Heather Whitney and colleagues investigated the B. pavonina iridoplasts using light and electron microscopy and found that their internal structure differs from conventional chloroplasts in that it is highly regular. The iridoplasts contain regularly spaced stacks of three to four thylakoids that resemble a photonic crystal and strongly reflect wavelengths of light between 430 and 560 nanometres, accounting for the leaves’ blue iridescence. In the Malaysian forests, the small amount of light that reaches the plant’s leaves is mainly at the green-red end of the spectrum. The authors show that the iridoplasts concentrate these specific wavelengths onto the plant’s photosynthetic apparatus, increasing the efficiency of its photosynthesis by 5-10%.
The authors conclude that, while chloroplasts are commonly thought of as structures that only convert light into chemical energy, they should also be considered as structures that control light propagation and light capture.