The leaves of the Malaysian tropical plant Begonia pavonina, also known as peacock begonia, have a curiously odd shade-metallic blue. Now, researchers reveal that its blue sheen helps this plant adapt to low levels of sunlight in the dim rainforests of southeast Asia.
Heather Whitney, from the University of Bristol, explained that the plant's odd color is due to its photosynthetic structures known as iridoplasts.
Iridoplasts provide cellular machinery for photosynthesis. They collect light to be used for synthesizing molecules that store energy.
Whitney and colleagues found that the B. pavonina's iridoplasts have very strange shape when they examined the cells of the plant under a microscope. The structures were stacked membrane upon membrane separated only by a thin film of liquid.
"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," said study researcher Matt Jacobs, from the University of Bristol.
"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."
The arrangement causes the light that hits the layers to get slightly bent producing the dramatic sheen. It also allows the structure to absorb more energy from the red-green light that abound in dark landscapes such as beneath the canopy of forests. Since only the blue light gets reflected back, it is the color that the human eyes can see.
Losing the blue light is not a problem for the Begonia plant's energy efficiency because most blue light gets absorbed by the rainforest that grows above it. The plants, however, become better at absorbing the type of light that is more abundant in the dim rainforest floor.
Researchers found that the effect called slow light in quantum physics combined with increased efficiency in absorbing red-green lights boosts efficiency of the Begonia plant's photosynthesis by up to 10 percent.
"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," the researchers wrote in their study, which was published in journal Nature Plants.
"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."
Researchers said it just shows the versatility of plants. Unlike animals that can easily move around when conditions are not favorable, plants have to find other means to adapt to the world around them.
"It's just wonderful and logical to think that a plant has evolved an ability to physically manipulate the lighting around it in a variety of different ways," Whitney said.
