SoylentNews

takyon writes:

The leaves of some species of the Begonia plant have a blue sheen when shaded. A team of scientists has found that chloroplasts in the leaves are optimized to collect green light in low-light conditions:

There are over 1,500 species of Begonia, and for a while, it has been known that some species show a bright blue sheen to their leaves. The biological function of this unnatural looking blue sheen was unknown: was it to deter predators or protect the leaf from too much light? This mystery has remained unsolved until a team headed by Dr. Heather Whitney at the University of Bristol's School of Biological Sciences began to study Begonias and noticed something new. They found that the leaves only developed a blue sheen when put in almost dark conditions and in bright light the sheen slowly disappeared.

Matt Jacobs, PhD student in the School of Biological Sciences and first author on the paper, said: "We discovered under the microscope, individual chloroplasts in these leaves reflected blue light brightly, almost like a mirror. Looking in more detail by using a technique known as electron microscopy, we found a striking difference between the 'blue' chloroplasts found in the begonias, also known as 'iridoplasts' due to their brilliant blue iridescent colouration, and those found in other plants. The inner structure had arranged itself into extremely uniform layers just a few 100 nanometres in thickness, or a 1,000th the width of human hair."

Photonic multilayer structure of Begonia chloroplasts enhances photosynthetic efficiency (DOI: 10.1038/nplants.2016.162) (DX)

Here we show that epidermal chloroplasts, also known as iridoplasts, in shade-dwelling species of Begonia, notable for their brilliant blue iridescence, have a photonic crystal structure formed from a periodic arrangement of the light-absorbing thylakoid tissue itself. This structure enhances photosynthesis in two ways: by increasing light capture at the predominantly green wavelengths available in shade conditions, and by directly enhancing quantum yield by 5–10% under low-light conditions. These findings together imply that the iridoplast is a highly modified chloroplast structure adapted to make best use of the extremely low-light conditions in the tropical forest understorey in which it is found.

Original Submission