Dr Corneile Minnaar, a pollination biologist from Stellenbosch University in South Africa has come up with a new idea of using quantum dots and 3D printed fluorescence box to track the fate of individual pollen grains. This novel, low-cost method could enable pollination biologists to track the whole pollination process from the first visit by a pollinator to its endpoint – either successfully transferred to another flower’s stigma or lost along the way.
Despite over two hundred years of detailed research on pollination, researchers do not know for sure where most of the microscopically tiny pollen grains actually land up once they leave flowers. “Plants produce massive amounts of pollen, but it looks like more than 90% of it never reaches stigmas,” Minnaar said. “For the tiny fraction of pollen grains that make their way to stigmas, the journey is often unclear—which pollinators transferred the grains and from where?”
Starting in 2015, Minnaar decided to take up the challenge through his PhD research in the Department of Botany and Zoology at Stellenbosch University (SU). He came upon the idea for a pollen-tracking method after reading an article on the use of quantum dots to track cancer cells in rats.
Quantum dots are very tiny semiconductor nanocrystals, behaves like artificial atoms. When exposed to UV light, quantum dots emit extremely bright light in a range of possible colours. Minnaar figured out that quantum dots with “fat-loving” (lipophilic) ligands would theoretically stick to the fatty outer layer of pollen grains, called pollenkitt. Furthermore, the glowing colors of the quantum dots could then be used to uniquely “label” pollen grains to see whether it reaches to stigmas.
The researchers’ next step was to find a cost-effective way to view the fluorescing pollen grains under a field dissection microscope.
“I decided to design a fluorescence box that can fit under a dissection microscope,” said Minnaar. “And, because I wanted people to use this method, I designed a box that can easily be 3D-printed at a cost of about R5,000, including the required electronic components.” Files for 3D-printing the box can be found here.
So far, the use of quantum dots and the 3D printed fluorescence box have proven to be an easy and cheap method to track individual pollen grains: “I’ve done studies where I caught the insects after they have visited the plant with quantum-dot labelled anthers, and you can see where the pollen is placed, and which insects actually carry more or less pollen,” Minnaar said.
But the post-labelling part of the work still requires hours and hours of counting and checking: “I think I’ve probably counted more than a hundred thousand pollen grains these last three years,” he laughs.