Shedding light on abcission
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| Coralie Lashbrook, assistant professor of horticulture, studies how plants abscise their organs. |
It wasn't long ago that days become shorter and temperatures grew colder, two signals that trigger many trees to shed their leaves. "But have you seen those oaks still holding on to their withered leaves?" asked Coralie Lashbrook.
Lashbrook, an assistant professor of horticulture and an affiliate of the Center for Plant Responses to Environmental Stresses, studies abscission: the shedding of plant organs. Her lab takes multiple approaches to determine how plants become competent to abscise in response to environmental or developmental cues. In the case of trees, some species respond to autumn abscission signals while others like oaks shed old leaves in spring. "We'd like to know how plants make such different decisions to shed or retain organs," Lashbrook said.
One lab project focuses on revealing molecular events that occur in specialized cell layers called abscission zones (AZs). Upon receiving an abscission signal, cells in these rows release enzymes that digest cell walls connecting neighboring cells. Because AZs are located at the base of plant parts, AZ cell separation leads to organ detachment.
"If we can capture just those abscission zone cells that separate in response to abscission signals, we can identify the molecular machinery that is causing that separation. Modifying parts of that machinery should let us improve abscission behavior in economically important plants," said Lashbrook.
Her lab is currently using technology called laser capture microdissection (LCM) to get to AZ cells of Arabidopsis flowers. First developed for isolating cancer cells, LCM can pluck out individual cells or cell types from sectioned plant tissue.
Graduate student Suqin Cai optimized LCM to isolate AZ cells of flower stamens abscising in response to pollination. From those cells Cai isolated RNA of sufficient quality and quantity to support gene chip studies of thousands of genes at a time. "The data identifies genes with potentially important roles in controlling abscission," said Lashbrook. "We're testing the impact of modifying their expression on post-pollination abscission."
Practical applications for abscission research are plentiful. Lashbrook noted that oranges are reluctant to let go of trees at harvest and require chemical pretreatments to loosen them. But soybeans drop their flowers in response to many environmental stresses, routinely lowering yield potential.
"If we understood how soybean makes this decision to shed its flowers so easily we could develop strategies to enhance pod set or retention," said Lashbrook. "By the same token, for oranges we could develop strategies to enhance fruit shed. Abscission regulators in Arabidopsis may suggest homologs we can modify to improve performance."
