How Roots Know Where to Grow
Scientists have discovered how plant roots feel their way around in darkness to burrow through soil. As the roots of a seedling grow and spread in the ground, they encounter obstacles such as rocks that block their way. Somehow the roots find a detour around these obstacles, and a new study, detailed in the Feb. 29 issue of the journal Science, tells how. "The key is in the fuzzy coat of hairs on the roots of plants," said study team member Liam Dolan of the John Innes Centre in the U.K. "We have identified a growth control mechanism that enables these hairs to find their way and to elongate when their path is clear." The roots find their way through the soil in a similar way to a person groping through the dark. If they come across some obstacle, they feel their way around it until they come to a point where they can grow again. The roots do this through a self-reinforcing chemical cycle. A protein at the tip of the root hairs, called RHD2, produces free radicals that stimulate the uptake of calcium from the soil. The calcium in turn stimulates the activity of RHD2, continuing the cycle. The cycle stops when the root hairs hit an obstacle because calcium can no longer be taken up. The roots then start to grow in another direction. "This remarkable system gives plants the flexibility to explore a complex environment and to colonize even the most unpromising soils," Dolan said. "It also explains how seedlings are able to grow so quickly once they have established," he added.
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