New Phytol. http://doi.org/zjh (2014)
Densely packed clusters of short, hairy roots enhance nutrient uptake in many plants. A series of controlled-environment experiments suggest that soil bacteria that stimulate plant growth promote production of these root clusters.
Although particularly important in nutrient-scarce environments, the factors that regulate root-cluster formation have remained unclear. Byron B. Lamont, of Curtin University, Australia, and colleagues tested the effects of two species of plant-growth-promoting soil bacteria on cluster formation in representatives of the major root-cluster-bearing families — Fabaceae and Proteaceae — under four nutrient regimes. The bacteria stimulated cluster formation in six of the sixteen treatments. The stimulation, which was underpinned by increases in root length and the number of clusters per unit root length, was more pronounced in the presence of nitrogen.
The researchers attribute the stimulation of cluster formation to bacterial secretion of the plant hormone auxin, known to promote the growth of these root systems. They suggest that the variable response observed stems from bacterial-dependent differences in auxin secretion, and plant-dependent differences in auxin sensitivity.
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Proceedings of the National Academy of Sciences (2018)