Plant Detective. His mission: To investigate one of the most common occurrences in nature, something that happens in plain sight billions and billions of times every year, every time a leaf falls from a tree or an apple drops to the ground.
It’s a process called abscission, when a plant’s organs — leaves, petals or fruit — naturally separate from the body of the plant. For a phenomenon so obvious, it’s something that scientists are still working to understand.
Walker, a biologist who has been at the University of Missouri since 1987, and his MU colleagues in the University’s Interdisciplinary Plant Group have been attracting international press for discovering links in the chain of genetic events that control abscission. With funding from the National Science Foundation, they tracked the process in a small flowering weed that grows in Europe, Asia and Africa.
What they’re finding could ultimately be used by farmers to control the timing of harvests, to give florists flowers that hold tight to their petals or even, as one British reporter suggested to Walker, to grow Christmas trees that wouldn’t drop their needles. “That impressed my siblings, two sisters and a brother, who aren’t scientists,” Walker said. “They had no idea what I did.”
His work also has impressed his colleagues in the field.
“John is a pioneer,” said Frans Tax, a plant biologist at the University of Arizona. “His research is an elegant combination of genetics and biochemistry. Because these genes are found in all plants, manipulation in crops to regulate abscission could be fairly straightforward.”
Before following Walker on his path to discovery, let’s review for a moment the case file on plant abscission: The autumn turning of leaves has always been part of the human experience, an activity has attracted at least as much interest from poets as from scientists.
When Walker does a PowerPoint presentation of his work he includes a citation from Emily Bronte:
Fall, leaves, fall; die, flowers, away;
Lengthen night and shorten day;
Every leaf speaks bliss to me
Fluttering from the autumn tree.
“That just about says it all,” Walker says.
Among deciduous trees, the kind that Bronte wrote about, abscission is used to conserve energy. Leaves change color and fall from trees as days shorten with approaching winter. Nutrients from the leaves are drawn back into the tree and stored for the next growing season. If the leaves were to stay on the trees through the winter the chances are good they would freeze and die and the energy they held would be lost.
But there are other reasons why plants use abscission.