The researchers found that GAs interact with other plant hormones such as auxin to tell the plant whether to concentrate on reaching for the sky or on building a bigger, better network of roots under ground. "The GAs and auxin are definitely talking, molecularly," said Busov.
Growing poplar seedlings mutated to make them GA-deficient, the scientists compared their root and stem growth to others that contained moderate amounts of GAs and a control group of wild-type plants with normal GAs. They found that more GAs, the more a plant's stem flourished, but its roots remained spindly. When GA production was shut down, either by using mutants that lacked the necessary genes or by silencing the genes that form the molecular on-off switch, the resulting plants looked dwarfed, but their lateral roots grew luxuriant and full.
Application of GA to the GA-deficient dwarf plants rapidly reversed the process. The plants grew tall, but their lateral root systems shriveled.
"Clearly, lack of the hormone promotes growth below ground, while the hormone itself promotes growth above ground," said Busov. "This is a natural mechanism that we don't know much about. It's always a tradeoff between growth above ground and growth below ground. Normally there is a fine balance, and this balance is a little disturbed under stress."
In a commentary on the research published in the same issue of the journal, Kathleen Farquharson, science editor of The Plant Cell, wrote: "This study provides important insights into how plant hormones regulate lateral root development."
|Contact: Jennifer Donovan|
Michigan Technological University